Recording Guitars

About this Pack

This pack was originally written as part of a PGCE I took at The Walford & North Shropshire College. I wrote it in the spring of 2001, and originally recorded some examples on an old Fostex 8-track reel-to-reel machine. I might get round to putting them up as MP3s, or I might not. Let me know if you want them.
Get in touch if you want a copy of the full pack. There was talk of publishing it, but that didn't really make sense in the end so I've stuck it up here. Let me know if it's useful.

Cheers

Matt Bellingham September 2003

Welcome What Recording Guitars is, and how to use it.
Unit 1: Sound and Acoustics A brief look at what sound is, how it is created and how it acts in open and closed spaces.
Unit 2: Microphones Covering the different types of microphone, their sound characteristics and directionality.
Unit 3: Recording Electric Guitars This unit covers the use of various microphone techniques in recording electric guitars.
Unit 4: Recording Acoustic Guitars Covering the relevant techniques used in recording acoustic guitars. Also looks at some interesting production ideas.

Answers to self-assessment questions | Unit 1 | Unit 2 | Unit 3 | Unit 4 | Congratulations!

Welcome!

Have you ever wondered how the great guitar sounds on your favourite albums were recorded? Why some 'classic' sounds have never been bettered? How strange, special guitar effects are created? How microphones actually work?

If you've answered "yes" to any or all of these questions, then you can find the answers in here. There are also answers to questions you didn't even know you wanted to ask…

So what is this pack?

Recording Guitars is a basic course for learning how to record electric and acoustic guitars. It also covers basic acoustics and microphone theory. It is split into four units…

Who is it for?

Recording Guitars has been written for almost anyone who is interested in learning more about the theory and practice of audio engineering. It is equivalent in level to the AS and A level Music Technology sections on recording, so it is expected that you will have experience equal to Music GCSE level.

Care has been taken in writing this pack to make it accessible to those who have no previous formal academic music qualifications. To get the most from it, however, it is assumed that the reader is an informed enthusiast who wishes to further their knowledge. You must be able to use a mixing desk.

What do I need to have to work through this pack?

It is expected that you will be working through this pack at a studio. It may be a home studio, one at a school or college, or a commercial studio. However, you must be somewhere where you can get your hands on the following…

What do I have to do?

The pack is designed to be a practical course, and the majority of the work you need to complete is practical

There are short self-assessment sections at the end of each unit. These are based on the text in each unit. It is important to complete these before you move on; they act as 'revision' for the information you have covered, and if you find you have any gaps in your knowledge you can look back and ensure you understand before moving on.

So what do I do now?

Well, how about turning to Unit 1?

Unit 1: Sound and Acoustics

In order to understand how to record sound, we need to understand what sound is. Simple, I hear you cry. Well…

This unit is all about what sound is, how it is produced, what elements it has and how these are measured. We'll look at how sound acts in natural spaces, including reverberation and echoes. The unit also covers some problems we can (and will) encounter when dealing with sound.

What you'll need for Unit 1

Good Vibrations

Sound is produced when an object vibrates and causes the air around it to move. The object is the sound source, and could be a Steinway grand piano or a sneeze; the theory's the same.
The sound source causes the air particles to push and pull against each other, much like a three-dimensional version of ripples in a pond.
The pushes in the air are called compressions, as the air particles are compressed together.
The opposite pulls are called rarefactions, as the air particles pull apart (or rarefy).

The rate at which the source vibrates (or oscillates) is the frequency of the sound wave it produces. Frequency is quoted in hertz (Hz), or cycles per second. For example, the note A has a frequency of 440Hz. This means that to play an A, the sound source must oscillate 440 times every second. 1000 hertz is 1 kilohertz (kHz).
The amount of compression and rarefaction in the air as a result of the oscillating sound source is the amplitude of the sound wave. Amplitude is the loudness of the sound when it is heard.
The distance between two adjacent peaks of compression or rarefaction as the wave travels through the air is the wavelength of the sound.
The sound wave can be plotted on a graph, such as the one below. The compressions are shown as positive, and the rarefactions as negative. The wavelength has been labelled t. This graph shows the waveform of the sound.

Look again at the questions at the start of the unit. Do you feel as though you could answer them now? Have a go; if there's an area you're unsure of, re-read the unit up to here. Don't worry about all the terminology yet. It's more important that you understand how sound works.

Phasers on Stun

No, nothing to do with Start Trek. We need to address the issue of phase cancellation, and to do this we need to do a little experiment.

This is where you'll need your stereo system or studio monitors. Cue up a recording, preferably something in mono, such as an old jazz or blues track. Place the speakers close together and play the track, paying particular attention to the timbres (sound colours) of the instruments and the overall volume.
Now, reverse the hot and cold (red and black) connectors on one of the speakers, leaving the other speaker as it is. Play the track again. What difference has this made?

Do not move on until you have tried this and heard the difference in sound.

What you have just experienced is phase cancellation. Phase problems are the bane of every engineer's life (professional life, anyway), so it's vital to understand what it is and how to avoid it.
The first play of the track should have sounded as it was intended to sound. By comparison, the second (inverted) play will have sounded weak, some instruments will have barely been audible, and the whole track will have been a lot quieter.

But why?

To answer that question, we need to look at what happens when two identical waves are played at the same time.
Remember that waveform graph we looked at? If there are two identical sounds playing at the same time, we can see what the result would be by adding the two graphs together. All you need to do is see where the waves are at any particular point in time, and add the two points together.

The experiment with the speakers demonstrated phase cancellation. With the speakers wired normally, the signals would have been in phase, and the resultant waveform would have been the same sound, only louder.
Once the speaker connections had been reversed, one speaker would have been out of phase, playing the same signal but with the compressions and rarefactions reversed. When combined with the original signal (played by the first speaker) we had the audible results; some sounds would have been almost completely cancelled out, and the overall volume would have been dramatically reduced.

Echoes of the Past

One more piece of sound advice (sorry) is one of reflection. No, nothing to do with mirrors. We're talking about the reflection of the sound waves that we've looked at so far.

Go into your reflective room (bathroom, stairwell, hall…anywhere where there are lots of solid surfaces such as wood, concrete, tiles or glass) and make some noise! A handclap, play an instrument or treat the room to your best Sinatra melody. Now, take your soft object (duvet, blanket or such like) and cover as much of the room as possible with it. Play/sing again. What has happened to the sound of your performance? Which did you prefer? Why?

The two 'performances' that you gave (I hope you didn't feel too stupid) should have sounded different. The first would have been with the natural reverberation of the reflective surfaces, as shown in this diagram. The surfaces allowed the sound waves to 'bounce off' and reflect back to you. The direct sound would have been the path from your hands clapping to your ears.

These first 'bounces' are called early reflections. The sound waves continue to bounce around the room, gradually getting quieter as they run out of energy.
The second 'performance' still had some of these reflections, but some others will have been 'soaked up' by the soft item you used. This is an example of absorption, where the energy in the sound waves is not reflected but instead is converted into heat.
The result is a room with fewer reverberations. This makes whatever is happening in the room sound different. Have you ever wondered why singing in the bath is such an enjoyable experience?

Maximum Volume

Finally, how loud is loud?
We need a way of measuring how loud something is. The actual movement of air is known as the Sound Pressure Level, most often called the SPL. The higher the SPL, the louder the sound.

The SPL is measured in decibels (dB), with 0dB being the threshold of hearing (the point at which our hearing starts). Our pain threshold is said to start at around 100dB, with a plane takeoff at about 120dB. Many rock concerts and nightclubs produce SPL's in excess of 140dB's, so it is imperative to wear appropriate hearing protection at all times.

You need your ears for a job like this.

Unit 1 Questions

  1. What are sound waves?
  2. If the frequency of a sound is increased, what is the audible effect?
  3. If a sound is made louder, which element of the sound wave has altered?
  4. Briefly explain what it means when two waves are described as being in phase.
  5. What happens when the two waves start to move out of phase?
  6. How are reverberations (or echoes) created?
  7. How can these reverberations be reduced? What is the audible effect on the room of having fewer reverberations?

Unit 2: Microphones

This unit is all about the 'ears' of the recording world. We'll be looking at the different types of microphone and the varying ways they 'hear' sound. We'll also look at some technical jargon that you'll need when we actually start recording some music!

What you'll need for Unit 2

What Does A Microphone Do?

A microphone is basically a transducer. A transducer converts one type of energy into another. In this case, the microphone converts sound from an acoustic form (the sound waves we looked at in Unit 1) into an electrical form.

Connect a microphone to your mixing desk or tape recorder. Make any kind of noise you want, and set the desk or tape machine so that the recording level meter moves as you make this noise. Now try making the same noise louder, and then quieter. What happens to the meter reading?

Once the recording level had been set, the same noise would have resulted in the same change in level on the recording meters. A quieter noise would result in a lower meter reading, and a louder noise would result in a higher meter reading. The changes in amplitude in the sound wave are converted into changes in voltage by the microphone. An increase in amplitude results in an increased voltage, which is displayed by the recording meter. Lower amplitude is converted into a lower voltage output.

Types of Microphone

There are four main designs of microphone. All microphones are made to one of the four designs, just as cars are made to the same basic design.

Dynamic Microphones

These microphones are the simplest to produce, which also makes them the cheapest. The sound waves hit the diaphragm (a thin plastic film) which causes it to move. This, in turn, moves the attached coil in a magnetic field, which creates an electric current.
Dynamic mics are relatively cheap, and are rugged, which makes them ideal for live performance as well as studio work. They can also tolerate extremely high sound pressure levels (SPL's). They require no power supply, as the microphone contains no electronic circuitry.
The coil restricts the diaphragm's movement somewhat, which means that dynamic microphones are not as effective at picking up high frequencies as other microphone types. They are therefore used most often on instruments that do not create many high frequencies.

Condenser Microphones

Condenser microphones are more complex in operation than dynamics, and as a result are both more expensive and less hardy; dropping your expensive condenser is never a happy occasion.
They work by creating a current in between two plates, one of which is the diaphragm. When the sound waves hit the diaphragm and make it move, this creates the signal.
As you can see, this requires a complex electrical circuit, which also needs powering. This power can come from either a battery or from the mixing desk (a process known as phantom powering, as the source of the power is spookily invisible!
The big advantage of this design is that the diaphragm can be made just a few microns thick and extremely light; this means the microphone can respond well to high frequencies. Condenser microphones are also very sensitive.

Ribbon Microphones

Ribbon microphones are very similar to dynamics, except that a single flat 'ribbon' replaces the diaphragm and coil.
The big selling point of ribbon microphones is that the sound they produce is very 'smooth' and natural. They are popular in classical recordings because of this.
The ribbon picks up sound equally from either side; we will look at this later.
Despite their sonic benefits, ribbon microphones are not used often. They are expensive and fragile, and many models used today are vintage originals. Studios with such mics are usually rather attached to them.
Ribbon microphones are characteristically large; many people think of the classic 'BBC' style microphones from the age of the wireless broadcast…

Pressure Zone Microphones (PZM's)

These microphones are rather unusual. They are often called 'boundary' microphones, as they were designed to be placed at a boundary; the floor, a wall, and so on.
The microphone is basically a pressure capsule that sits on a base plate. There is a small gap of air in between the plate and the capsule. As the sound waves hit the plate they are reflected onto the capsule. The changes in air pressure are then converted into an electrical signal.
These microphones are capable of very natural sound reproduction, and are used quite often in a studio environment. They can be quite difficult to use, however; it is not possible to 'aim' a PZM mic at a performer, or to use one on a microphone stand.

List the different microphones you have in your studio. What types of microphone are they? This is very important for knowing what they will be useful for when you are recording. If you can't find anything written on the mic itself, try to find the specification sheet that came with the mic. If that's missing (and there aren't many studios where all the paperwork is in one place), have a look at the manufacturer's website. You need a list of microphones and mic types before you go any further!

There are two more questions to be answered about microphones; where do they 'listen' from, and what directions to they listen to?

Fire?

The first question seems obvious, but it's surprising how easy it is to be fooled.
Some microphones pick up sound from the side; the question is…which side? Most mics have this information in their specification sheets, but few have any hints actually on the mic itself. If in doubt, experiment! The diagrams on the left show these side fire microphones.
Other microphones pick up sounds from the front; these are the microphones that you 'point' at the sounds to be recorded. These mics are known as end fire microphones, an example of which is shown in the diagram on the right.

Polar Patterns

The other matter is one of direction. Not all microphones pick up sound in the same way. Some pick up sound equally efficiently no matter where the sound is coming from; they don't need to be 'pointed' at the sound source. Other microphones are designed to respond to sounds from a particular direction.
This element of the microphone's design is known as the pickup pattern. There are three main types of pickup pattern;

Omnidirectional

Bidirectional

Cardioid

Hypercardioid

Get your list of microphones that you made for the last exercise. Now, have a look on the body of the microphone. There is normally a (very) small pickup pattern diagram on the microphone. It will match one of the diagrams above. Some of the more expensive condensers have switchable polar patterns. These mics have a switch with more than one pickup pattern drawn above it. Take your list, and add a third column; pickup pattern. Make a note of the pattern (or patterns) that your microphones have. You should now have a list of the microphones you have at your disposal, which looks something like this…

Microphone Mic Type Pickup Pattern
Shure SM58 Dynamic Cardioid
AKG 414B Condenser Switchable; Omni/Cardioid/Bidirectional

Unit 2 Questions

  1. What is a microphone's purpose; what does it do?
  2. Give two reasons why dynamic microphones are sometimes marketed as 'live' mics rather than 'studio' mics.
  3. Conversely, condenser microphones are often seen as the 'studio' rather than the 'live' microphones; again, give two reasons why.
  4. State what type of microphone pickup pattern you would wish to use for each of the following applications. Give reasons for your answers.
    An interview with the interviewer and interviewee sitting opposite each other
    A live vocal microphone. The microphone will need to pick up the vocalist and reject other sounds
    A folk recording with the musicians set up around one microphone
  5. How can we reduce the bass on a recording, using only the microphone?

Unit 3: Recording Electric Guitars

Now's the time to apply some of your hard-earned sound and microphone knowledge in the pursuit of some great guitar sounds. This unit is all about how to record the sounds produced by the electric guitar. We'll look at which microphones to choose and where to place them for various different tones and effects.

What you'll need for Unit 3

You'll need the CD on hand from here on in. The track numbers will be next to the relevant text so you can hear the techniques being explained. It's a good idea to listen to the recorded examples through speakers, and then headphones. Speakers, properly positioned, can recreate sound very accurately. Headphones will make the differences between examples much clearer; they are our aural microscopes, and are very useful when used in that capacity. If you are listening on a portable CD player with fixed speakers it would probably be best to listen on headphones; you'll sacrifice some of the 'realism', but you'll get more information out of the recordings.
All the electric guitar parts were played on a Fender Stratocaster through a Tech 21 Trademark 60 amplifier.
The dynamic microphones used were Shure SM58's. These microphones were designed 50 years ago, and have become classics. They are primarily used for vocals, but also work very well with electric guitars and snare drums.
The condenser microphones used were Shure AM16's. These microphones are a recent design, which attempts to give a flat frequency response and a good dynamic range.

Up Close and Personal

In the average, everyday world of a guitar amplifier, there are two main jobs. The first is to alter the sound in some way; to make the (rather boring) output of an electric guitar into something incredible and mind-blowing…or at least listenable. The second job is to make the whole thing louder so that it can compete volume-wise with the kind of SPL's being created by the drums, the neighbours banging on the walls, and so on. If we want to record the guitar whilst all of this other noise (sorry, music) is going on, we'll need to find a way of rejecting all of the unwanted sound.

We can do this by…

British or American?

Many of the classic rock guitar tones have been recorded either in Britain or by British engineers. Hendrix, Clapton, Page…their recorded guitar sounds have become legendary, and are copied time and time again.
The 'British' sound was created by using dynamic microphones. As you know, dynamic mics are less sensitive to high frequencies and so have a mid-range biased, 'fat' sound. They can also handle the extreme SPL's that a Marshall stack can produce!
The 'American' rock sound (think of The Byrds, The Eagles or Ry Cooder) was produced by using a condenser microphone on the electric guitar. This produces a sound with more high frequencies, making it more incisive and less 'fat' and 'warm'.
So which one? Well, if you like the sound, you've used the right mic. Try whatever you've got, as each microphone has a different sound, much as different guitars and amplifiers have different sounds.

Where Do I Point It?

The section of speaker the microphone is pointed at will profoundly affect the tone of the recorded guitar. The choice of where to place the microphone is the essence of acoustic sound engineering.

Dust Cap trebly sound with lots of bite
Mid Cone fewer high frequencies, slightly warmer and fatter
Outer Edge significantly fewer high frequencies, much warmer and fatter

Use the technique described above and record your guitar amplifier's cone at different points with a dynamic mic, then a condenser mic. Make a note of the change in tone that results from each change. Which do you prefer? Why? Compare your results with those on the CD; do they sound different? If so, consider why that might be the case…

Everyone has different taste; most engineers have slightly different ideas on the perfect tone. The trick is to know what tone you want, and how to get it. Experimenting like this helps you to hear how slight variations can yield surprising results.
You might find that you immediately prefer one particular combination of microphone, mic placement and amplifier. If you were to use a different mic, or a different amp, you would record a different tone.

Bass Lift

As we saw in Unit 2, the proximity effect is an increase in a microphone's bass response when the mic is very close to the sound source. Many microphones have a bass lift, which can counteract this added bass.

If any of your mics have a bass lift switch on, try recording with the lift ON and OFF. Again, ask yourself which you prefer. Compare your results with the CD. Try to imagine what styles of music would call for a boost or cut in the guitar's bass response.
Some styles of music require a guitar sound with lots of low frequencies; jazz guitar is nearly always very bass-heavy. Other styles, such as funk, require the bass frequencies to be attenuated (reduced) in order for the sound to blend in with the other instruments. The bass lift switch is one way in which to do this.

Ambience and Room Sound

In Unit 1 we looked at the way sound waves move in a room. We looked at reverberation, and you made some noise in a reflective, reverberant environment.
When we hear a guitar amplifier, we don't hear it from a close miked position; put your head next to a cone in a Marshall stack and you may decide not to do it again. We hear it from a distance, and the sound we hear is a mixture of direct and ambient sound. So how do we capture that?

The answer is to position the microphone so that it 'listens' to both the direct and reflected sound waves.

To find the best point for the microphone, move around the guitar amplifier and listen for the perfect mix of direct and ambient sound. Once you've found that point, place the microphone where your ears are. The point of the desired sound is known as the sweet spot (or hot spot).
Moving closer to the amplifier will increase the direct to ambient sound mix. Moving away from the amplifier will increase the ambient to direct sound mix.
The amount of reverberant sound is dependent on the room. As we have already proved, hard, reflective surfaces reflect more sound than soft surfaces. We can tailor the room's characteristics by adding absorptive materials (drapes, rugs, carpet, foam etc).

Try recording the amplifier from various distances. How does the change in distance affect the recorded sound? What about the guitar's tone? Is it more or less 'realistic'? Also try to alter the room's acoustic using some kind of absorptive material. You could even record the guitar amplifier in a different room altogether. What effect does this have on the guitar's tone?

The microphone picks up more direct sound and less ambient sound the closer it is to the amp. As you move it further away it picks up less direct sound and more ambient sound. Many people feel the guitar sounds most 'natural' when there is an element of room sound present, but you may disagree. When the room's acoustic is changed, the recorded tone also changes. The use of screens, drapes etc is an important part of engineering.

Mix and Match

All microphones sound slightly different, and we've already seen how different areas in the room sound slightly different.
Given a little extra time, why not try to construct the perfect guitar sound?
Instead of having to make do with the sound of one microphone, we can take the desirable qualities of one mic and mix them with a second mic type.

The classic mix is a dynamic and a condenser used on the same amplifier. The dynamic has a punchy, mid-range based sound, and the condenser has a natural, open sound. Mixing the two can give an engineer access to a whole array of tones.

The classic technique is to use the dynamic as a close mic, and to use the condenser's extended high frequency response to pick up some ambient sound. By altering the balance between the two, many different tones can be achieved.
This technique is all about getting the best of both worlds, so combine your favourite close-mic microphone and position with your favourite ambient microphone and position. Listen to the close mic, and slowly fade up the ambient mic until the mix is to your liking.
Sometimes two microphones that work well on their own do not combine well, so once you've set the mics up you may need to do a little fine tuning. The mix of the two mics is also a matter of judgement; basically, if it sounds good, it is good!

String Thing

A great way to add some high frequency 'zing' to the recording is to mic up the strings of the electric guitar. Solid body electrics are not designed to project sound, and on their own sound thin and uninteresting.
Add the string sound to the output from the amplifier, and the result is a clear, crisp and well-defined guitar tone. Be sure to have the amplifier in a different room to the guitar if you want to avoid the string mic picking up the amplifier.

Try close-miking the electric guitar's strings while also close-miking the amp. Mix the two signals together as you did in the last exercise. Are there any potential problems with this way of working? Listen to the CD track for a clue as to the potential pitfall…
Combining the two signals should give the amplifier's tone a bright attack, almost like an acoustic guitar. The main problem can come from the 'strings' microphone picking up the amplifier. Putting the guitar player in one room and the amplifier in another can solve this.

Phased Again

As we saw in Unit 1, phase problems cause cancellations in certain frequencies leaving the resulting sound thin and lifeless. Unfortunately, phase problems can occur whenever two or more microphones are used together.
The problems happen when the microphones pick up the same sound waves at different points. If one microphone picks up a compression in the sound wave while the other mic picks up a rarefaction, phase problems occur.

Coincidents?

The answer to this problem is to position both microphones so their capsules (the end of the mic that contains the diaphragm) are as close as possible to each other. By setting the mics up like this, both mics will 'listen' to the sound wave at exactly the same point, therefore reducing the chances of phase problems. This is known as a coincident pair.

Try the coincident pair as described above. How will having two different mic types together affect the recorded tone?

The mix of the two mic types is the main variable factor in this technique, and once again it is a matter of taste. The dynamic mic will have a 'warmer' tone, and the condenser will pick up more high frequencies. Once again, the choice is yours…

Ribbon Mic

We looked at the ribbon microphone design in Unit 2. These mics are good for use on guitars because of their clear, realistic sound. Ribbon mics are bidirectional; that is, they 'hear' sounds in front and behind them. When used on guitar amplifiers ribbon mics 'hear' both the direct sound from the amp and the ambient sound.

If you have a ribbon mic, or a condenser with a switchable pickup pattern, record the amplifier as described above. How could you mimic the bidirectional's characteristic pickup pattern without a bidirectional mic?

The bidirectional pickup pattern sounds very 'open' and realistic because it picks up both direct sound from the amplifier and reflected sound from the room. We can mimic this by setting up two cardioid mics next to each other. All we need to do is to aim one mic at the amp, and aim the other mic at 180° from the first. This set-up also gives us control over how much ambience we introduce into the signal, as we can fade the 'ambient' mic up or down as required.

Open Back, Closed Back

Guitar amplifiers make their wondrous noise through speakers. These speakers are housed in a cabinet or cab. Guitar cabs are either open back or closed back. This refers to the rear of the cab and whether the area behind the speaker is covered (closed) or open to the elements (open). Most guitar cabs are open backed, while certain classic designs (Marshall, for example) have closed backs. Closed back cabs are designed to reflect all the sound waves out of the front of the cab. This means that the front of the amplifier is the main area to mic when recording.
Open back cabs are designed to produce sound from both the front and back of the cab. When listening to such an amplifier, we hear sound from all around the amp, not just from the front.

If the sound from the rear is such an important component part of the amp's tone, why not record that too?

The sounds from the front and the rear are liable to phase problems (yes, them again) so listen carefully to how changes in mic positioning affect the recorded tone.
You can listen to the front mic and blend in some of the rear mic, or visa versa.

Using what you have learned, set up your favourite close mic combination on the cone of the amp. Then set up the same combination on the rear of the amplifier. Listen to the mic outputs separately. Do they sound the same? Try moving the mics until you get the tones you want. Try mixing the two mics together.

The front and the rear of an amplifier sound quite different. The two tones can be complementary, in which case they can be blended very successfully. The front mic need not be the dominant signal.
Engineers often use the rear mic for the main sound, and blend in a little of the front mic to achieve the desired result.
As with all microphone use, the taste and judgement of the engineer is the main guide to what mics are used and where they are put. Try as many variations as you can.

Speaker Simulation and Amplifier Simulators

The final method of miking a guitar involves no mics!
Over the last few years, speaker simulators have got better and better. Their job is to mimic the sound of a speaker cone being miked up. The speaker simulator is then fed into the mixing desk and treated just like the output of a microphone. This saves time and money; no expensive mics or expensive people who know what to do with them!
Amplifier Simulators are even more advanced. They replace the amplifier as well as the speaker and the microphone. The guitar plugs into the modeller, and the output goes straight into the mixing desk. Modern units such as the Line 6 Pod (pictured) digitally replicate a host of expensive and rare amplifiers with excellent results.
The best simulators sound almost indistinguishable from the 'real thing'. The lack of reverberation or 'room sound' is the only aspect that makes the results feel 'fake' or 'cold'.

If you have access to one, try recording a guitar part directly through a speaker simulator or amp simulator into the mixing desk. Compare the recording process and the end result with using microphones. How does this method compare with the 'old fashioned' (!) way?

Every simulator has a different tone, just as different mics and amps have different tone. The results are, once again, a question of taste. Many musicians and engineers hate the idea of recording without using 'real' equipment. Many more love the speed and ease of recording using simulations of all the things that slow the artistic process of making music down. The simulators have yet to reproduce the 'feel' of an amplifier, the way it responds to the dynamics and touch of the guitarist. However, ask yourself if you could tell the difference if the guitar was just one instrument in a mix…

Unit 3 Questions

  1. List two techniques used to reduce spill when recording a guitar amplifier in a noisy environment.
  2. What is the difference between the 'British' and 'American' tones? Which mics create the sounds and how?
  3. How does moving the microphone away from the amplifier affect the recorded sound?
  4. How can phase problems affect a two-microphone set-up? How can the problems be solved?
  5. Why do we need to record the back of an open-back cab?
  6. What is the difference between a speaker simulator and an amplifier simulator?

Unit 4: Recording Acoustic Guitars

We've looked in some detail at recording electric guitars; this unit is all about using the same techniques on a different instrument. The differences between electric and acoustic guitars are many; they both have strings and frets, but from an engineer's point of view they are entirely different.
In this unit we'll be looking at how to mic an acoustic, what to mic it with, and some production tricks to make it sound fantastic. We'll also look into the weird and wonderful world of stereo miking.

What you'll need for Unit 4

First Things First

The first step in getting a good acoustic sound onto tape is to have a good acoustic guitar. Obvious I know, but the best that can be done with a bad sounding instrument is a fabulous recording of a bad instrument. Try to get the best instrument you can, and the best guitar player you can. The same goes for your choice of microphones, although if you have a few different types try them all to find the best sound. Remember that if it sounds good, it is good.

The recordings on the CD were played on a Taylor 314 and recorded using the same Shure AM16's and SM58's used on the electric guitars.

Which Mic?

The first choice is…dynamic or condenser? Well, listen to the first two acoustic recordings.
As we saw in Unit 2, dynamics do not have the same high frequency response as condensers. High frequencies are an important component in an acoustic guitar's tone, so the condenser's extended range is highly desirable. All subsequent recordings will be made using condensers.

Just as you recorded an amplifier using both dynamic and condenser microphones, it is important to record an acoustic guitar with both types too. Set up a dynamic mic about a foot away from the guitar, pointing at the guitar's body. The exact positioning isn't important here; we're listening to the microphone, not the mic's positioning. Compare the dynamic's tone with a condenser set up in exactly the same position. What is the difference between the two?

As you know, dynamic microphones don't have the same sensitivity to high frequencies that condenser microphones do. Acoustic guitars produce more high frequencies than electric guitars do, and so it is important that the right microphone is chosen. As ever, trust your judgement, but it is a useful rule of thumb to start with a condenser when working with acoustics.
All parts of an acoustic guitar produce sound. The tone of an acoustic guitar is the sum of many different parts of the guitar vibrating and producing sound waves. It is therefore quite difficult to use just one microphone to reproduce such a complex sound. However, it's very common to have a lack of time and/or microphones, so very often one mic is all that is available.

One very important point to remember is that, in order for the guitar's true sound to be captured, the mic(s) should be at least 1 foot (30 cm) away.

This is the BBC…

This technique has become a standard way of recording an acoustic guitar using one microphone. The microphone is aimed towards the end of the fretboard and at an angle so that it fires (or 'listens') across the soundhole.

Record the acoustic guitar exactly as described above. Try the 'BBC' technique with both dynamic and condenser mics, and compare the results with each other and with the CD. How do the two mic types compare? Try to describe the comparative tones of the two mics.

The dynamic microphone cannot recreate high frequencies as well as a well-designed condenser mic. However, if there is only one mic left in the box and it is a dynamic, this exercise should have least showed that it is possible to record an acoustic with a dynamic; it just isn't our first choice.

Additional Mics

The sound from one single mic can be augmented if you have the time, equipment and mixing desk channels at your disposal. For example, adding another condenser to the 'BBC' mic can add another aspect of the guitar's natural tone. Try adding a mic pointing below the bridge of the guitar as shown in this diagram. Listen to the sounds from the two mics separately and blended together.

Boom!

One thing you'll be tempted to do is to place a mic pointing into the guitar's sound hole. After all, that's the part of the guitar that produces the largest signal. However, the tone from the soundhole is most often boomy and unpleasant. The soundhole is only one part of the total guitar tone.

Set up a second mic pointing below the bridge as described above. Use condenser mics for both. Listen to the two mics separately; do either of them pick up the full tone of the guitar? Try blending them together to create a more realistic effect.
Try moving one of the mics so it points straight into the soundhole. How does it sound compared with the techniques tried so far?

The 'BBC' mic will pick up one aspect of the guitar's sound, and the 'below bridge' mic will pick up a slightly different one. Either of these mics will sound fine on their own, as both techniques are tried and trusted classics for getting a good, one-mic tone. However, blending the two together should give us the ability to combine the good qualities of each technique, making a more realistic overall sound. The soundhole isn't a good place to put a mic, as your experiment should have proved. Moving the mic to either side if the soundhole reduces the bass frequency 'boom' and gives a more natural tone.

Another Combination

Another useful two mic technique is to mic the body of the guitar (the area below the bridge) to pick up the bass frequencies, and to place another mic to cover the neck. The neck of the guitar is the main area in which high frequencies are produced. A mix of the two microphones will produce a detailed, articulate tone.

Try miking up the neck of the guitar and mixing it with a mic on the guitar's body as described. Can you see how this technique could be useful in controlling the recorded tone without resorting to the mixing desk's equalisation (tone controls)?

The ratio between the two microphones allows us to alter the guitar's recorded tone. If we require more low frequencies we can boost the body mic's signal, and if we require more high frequencies we can boost the neck mic's signal. This technique allows us to balance the tone like a natural equalisation control, allowing us to alter the tonal balance without resorting to electronic circuitry.

Ambience and Sweet Spots

Just as we looked at using ambient microphones in recording, the same technique is very useful in recording acoustic guitars. Depending on what type of sound you're after and how good the room acoustic is, place the microphone from 1 foot (30cm) away to as far as you can.
Remember the sweet spots; walk around the room listening for the point at which you hear the ideal mix of direct and ambient sound, and place the microphone where your ears are.

Stereo Techniques

Most recordings are made by recording mono sounds and then panning them to different positions in the soundfield. True stereo recording is rather different.

Deep Space(d)

The most obvious way to record in stereo is to use two microphones, one for each ear. Two microphones used in this way are known as a stereo pair.

Remember phase cancellation? Well, it's back. If a stereo recording is played on a mono system (such as a tape recorder with one speaker), the left and right hand signals are added together. If we haven't tried to avoid phase problems when recording the result will be unpleasant.
Luckily, avoiding bad problems is fairly simple. There are two main ways in which to avoid it. The first is what's known as a spaced stereo pair adhering to the 3:1 rule. What this means is that, in order to avoid phase problems, the distance between the two microphones should be three times greater than the distance between the microphones and the sound source.

Set up a stereo pair using the 3:1 rule as described in the text. Try moving the mics further away from the guitar (and therefore further apart from each other) and try some recordings from different distances. When you listen back to your recordings, listen to the difference in tone that results from the different distances. Also, listen to the recordings though headphones and through speakers. Does this miking technique particularly suit one monitoring medium or is it good for both?

Moving microphones further away from the guitar should have reduced some of the high frequency 'zing' from the tone, and made it 'warmer'. This is a useful rule-of-thumb; moving the mics closer would result in a 'brighter' tone with more high frequencies.
This technique is commonly used for recordings that are for playback through speakers. Headphones still work with the information, but if the microphones are ten feet apart and we listen to the signals through headphones, it will feel as though our ears are ten feet apart!

The phase problems come from the fact that the two mics are 'listening' to the sound waves at different points. While one mic is picking up a compression the other could be picking up a rarefaction. How can we make sure that both microphones are 'listening' at the same point?

Coincidence?

A simple and highly effective answer is to position two cardioid or bidirectional microphones so that they are at 90° to each other with their capsules as close to each other as is practically possible. This technique is known as an XY Pair.
As the microphones are directional one will pick up the sound from one side of the 'soundstage' and the other will pick up the opposite side.
The only problem with these techniques is that they make no attempt to mimic the effect the head has in filtering sound waves.

Try recording with an XY pair as described above. Listen back to the results on speakers and using headphones as you did for the last exercise. How does this technique compare with the last stereo pair?

If the 3:1 stereo pair made our 'ears' seem too far apart when listening through headphones, the XY pair can fool us into thinking that we have no head at all, just two ears! This effect is very subtle, and most people don't find it intrusive or 'unnatural' sounding at all. XY pairs are great for most stereo recordings, and they sound equally at home on speakers and headphones.

Dummy Head or Binaural Recording

Some microphone companies manufacture a dummy head, like the one on the left, which is a head made from material that filters sound very much like our own heads do! Microphones are placed where the ears would normally be, so they pick up exactly what a person standing in the same spot would hear.
There are two cheaper ways to mimic this technique. The first is to separate two microphones with a foam disk. If the microphones are placed a heads width apart, the disk will mimic the head's acoustic shadow. The diagram on the right shows this technique.
Another way to mimic the acoustic shadow created by the head is to use…a head! Simply place a microphone next to each ear of the performer (or "dummy", as you're now technically required to call them). The recorded sound will be as close as possible to the sound heard by the performer. Omnidirectional mics are best here, as our ears are not directional.
A simpler and quicker version of the 'dummy head' technique is to put a single microphone (omni or cardioid) above the performer's head. This, of course, will be a mono recording.

Try to avoid the inevitable comparisons between your guitarist and the inanimate sound-filtering dummy they are now taking the role of. Try the dummy head technique described above, using two omnidirectional or cardioid mics right next to the guitarist's ears. If you're using cardioids, make sure the mics are pointing towards the guitar. Listen to the results on headphones and speakers; which do you prefer?
Also try the single mic version, and compare it with the stereo take.

The dummy head technique should almost exactly reproduce the sound heard by the guitarist. It will only do this through headphones, however. Dummy head (or binaural) recordings can be played through speakers, but some of the other techniques we've looked at are much better for speaker reproduction. Binaural recordings can be eerily realistic, and they are normally the performer's favourite technique as it makes the instrument sound just as they hear it. The single mic above the performer's head can work well, with a similar 'musician's perspective' on the recording. It is in mono, however, so can be played on speakers just as well as headphones.

Finally, here are a couple of ideas to make your acoustic recording more interesting.

Double Take

The first option is to double-track your guitar part. This means you simply record the same part twice. There will be variations in timing, tuning and dynamics between the two recordings. When they are played together, these 'imperfections' make the guitar sound 'thicker' and more interesting. Panning the guitars to either side of the stereo sound spectrum can increase the sense of depth.
The next option is to play the same chords in both parts, but for each track to use different inversions.
Try double-tracking a guitar part exactly; how well can your guitar player accomplish this? Once you've tried that, get your guitarist to record two parts playing the same chords but using different inversions in each take. A good way to do this is to use a capo on the guitar for one take.
Double tracking is a very difficult technique for the instrumentalist. It is also one that is very rarely required. Guitarists need to practice such a technique in order for it to be effective. The results can be very impressive, however, giving a depth and interest to the part. There is great scope for experimentation here for the creative engineer.
The final option is to combine a track of acoustic and a track of electric guitar. This is a very common trick to add clarity and to an otherwise bass-heavy electric sound.
This technique has been used on hundreds of albums. The acoustic guitar's clarity and definition blends wonderfully with a slightly overdriven electric guitar part. Skilfully played, the two tracks blend seamlessly into one another, producing a guitar sound that truly is 'the best of both worlds'. Try altering the electric guitar's tone until the sound is exactly what you want.

  1. Acoustic guitars are normally recorded using which type of microphone? Why?
  2. What is the idea behind blending the signals from two microphones when recording acoustic guitars?
  3. Why is the soundhole rarely miked up?
  4. How many microphones do we use to record in stereo? Why?
  5. Draw the following stereo pairs…
    3:1 Spaced Stereo Pair
    XY Coincident Stereo Pair
  6. Briefly describe what binaural (dummy head) recording is.

Unit 1: Sound and Acoustics

Self Assessment Answers

  1. Sound waves are movements in the air. They are variations in air pressure that are caused when an object (the sound source) vibrates.
  2. The frequency of a sound is the rate at which the sound source vibrates. More vibrations (or a higher frequency) create a higher pitch.
  3. If a sound is louder, its amplitude has increased. Amplitude is the amount of compression and rarefaction in the sound wave.
  4. When two waves are in phase, they combine to make a wave that has twice the amplitude. This means the sound is the same, only louder!
  5. If two waves are out of phase, they combine to make a wave that is the point-by-point sum of the two. If a compression of one is combined with a rarefaction of the other the two waves will cancel each other out.
  6. Reverberations, or echoes, are caused when sound waves are reflected off surfaces back to the listener.
  7. Reverberations can be reduced by 'soaking up' some of the sound waves using acoustically absorbent material such as a duvet or carpet. These materials stop the waves from 'bouncing' back to the listener. This has the effect of making the room less live (reflective) and more dead (less reflective).

Unit 2: Microphones

Self Assessment Answers

  1. A microphone is a transducer; it changes energy from one form into another. In this case, microphones convert acoustic energy (the sound wave) into electrical energy (a change in voltage).
  2. Dynamic microphones are suited to live work because they are;
    Cheap to produce (and replace!)
    Rugged
    Able to handle high sound pressure level (SPL's)
    Simple in design and don't need powering
  3. Condenser mics are ideal for the studio because they are;
    Expensive and fragile; not to be dropped!
    Complex; they need powering
    Very efficient at picking up high frequencies; excellent sound quality
  4. A bidirectional pickup pattern would be ideal for an interview.
  5. Live vocal mics have to reject the sound that arrives from the rear and the sides. This means that a cardioid pickup pattern would be the best choice.
  6. If an equal response all around the mic is required, an omnidirectional
  7. mic is the correct choice.
  8. If the microphone is picking up too much bass (possibly the result of the proximity effect), try turning the bass lift on.

Unit 3: Recording Electric Guitars

Self Assessment Answers

  1. To reduce spill, we can place the mic as close as possible to the amplifier, and use a cardioid microphone. This mic will reject the sounds from the rear and sides, thus reducing the amount of unwanted signal.
  2. The 'British' tone is produced using dynamic microphones. Dynamics do not pick up higher frequencies, making the recorded tone sound 'fat' and 'warm'. The 'American' sound is the product of using condenser mics. As their high frequency response is more efficient, the resultant tone is less 'warm' and clearer.
  3. When the microphone is moved away from the amplifier, it picks up less direct sound and more reverberant sound. Basically, the further away from the amp the mic gets, the more it becomes an ambient mic. Ambient mics pick up the room sound rather than specific instruments.
  4. If one microphone picks up a compression in the sound wave and the other mic picks up a rarefaction, the two mics will be out of phase. Simply moving one mic slightly can solve this problem.
  5. The back of an open-back cab produces nearly as much sound as the front. Both sides are necessary for a realistic recording.
  6. A speaker simulator mimics the sound of a speaker cone. It must be used in conjunction with an amplifier. An amplifier simulator also does this, but it also copies the sound of the amplifier itself.

Unit 4: Recording Acoustic Guitars

Self Assessment Answers

  1. Acoustic guitars are normally recorded using condenser microphones.
  2. This is because their efficient high frequency response captures the tone of the acoustic guitars very well.
  3. The blending of two different mics is a technique used to recreate the guitars complex tone. Different parts of the guitar produce different sounds; by miking more than one place we can create a composite mix that seems more realistic than just one microphone.
  4. The soundhole's tone is 'boomy' and bass-heavy. The tone either side is much better balanced.
  5. Stereo recording needs two microphones. This is because we are recording separate signals for each ear. I don't need to tell you that we have two ears, do I…?
  6. Binaural recordings are those made by using a dummy head. The head has microphones placed where the ears would be, so that recordings made using the head should 'hear' sounds exactly as we hear them.

Congratulations!

You've just completed an intensive course on sound theory, microphone theory, and specialist miking techniques and strategies. You have also covered some fundamental theories, such as stereo recording, that can be used in any engineering work.
You now have enough knowledge to engineer guitar recordings to a professional standard.
If this has whet your appetite, many courses are run at colleges and universities all over the country that cover engineering, production and recording.

Good luck!



© Matt Bellingham 2003 – 2006

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