Digital Audio Recording Tips

• Miking
  
• Effects
  
• EQ
  
• Mixing
  
• Mastering 

Excerpt from the book - Sound Engineering Basics by Andy Bramhill.

Basic Microphone mechanics and techniques

When miking up any instrument there are three main factors to bear in mind.

1. Positioning of the musician
2. Choice of mike
3. Positioning of the mike

When you hear an instrument in a recording studio or inside any room, you are not only hearing the sound of the instrument itself but you are also hearing the sound of the instrument mixed with the 'sound of the room'. That is the reflections of the sound-waves off the walls, ceiling, floor and any objects there may be in the room. These reflections of sound combine with the actual sound of the instrument in a subtle and natural way. Use of this phenomenon is the secret to a good recording as the placement of the musician is often the key to a good recording.  

To better illustrate this you might imagine the sound of a trumpet for example being played in the middle of a field. It still sounds like a trumpet but tends to be a little thin and raspy. Now if you take the same musician and get him to play the instrument in your front room it will sound very different, it will seem much louder and also it will seem to have a fuller quality to it.

The difference in sound is due of the reflections of sound-waves. In the field, you are hearing mostly the bare, crude sound of the instrument, direct with little or no reflected sound. In your front room you are hearing the sound of the instrument mixed in with the reflected sound bouncing around off the walls, floor, furniture etc. So you are actually hearing the sound more than once, hence the apparent increase in volume.

When sound hits a surface, depending on what material the surface is composed of it will absorb a part of the sound and reflect another part. For example, glass tends to reflect the higher frequencies and absorb the lower frequencies or allow them to pass through.  A carpeted wooden floor will absorb most of the high frequencies and reflect the low/mid frequencies. Wooden panels will act as a diffuser, ie not make the sound bounce about like balls on a billiards table but will spread the whole sound around a little...  diffuse it.

When you are confronted with a musician in a small or medium sized recording studio you should try and experiment with different placement of the musician within the room. (If you are lucky enough to get the time to do this and to be working with a patient musician). With a little bit of practice you will be able to stand in the room with the musician and distinguish the sound of the instrument from the sound of its reflections. You will also get to know 'the sound' of your particular recording room.

The positioning of the musician in relation to the walls, windows etc depends entirely on the actual instrument being recorded and the overall sound you are trying to get. Remember that one of the secrets to good recording is to be able to get a great sounding instrument and having to use little or no eq. You should be able to do this by positioning the musician well, choosing the right mike and positioning it accordingly.

Once you have the musician positioned correctly and the instrument sounding more or less as you need it then you can start thinking about what sort of mike you're going to use.

Basically the first (and most important) desicion will be between whether to use  condenser or dynamic mikes .(*See the explanation on the difference between condenser and dynamic mikes.)

Condenser mikes are very sensitive, and tend to pick up everything the ear can hear and more. The sound they reproduce tends to be very clean and clear...    at times too much so. For example, a condenser mike will reproduce the sound of a saxophone EXACTLY as it is sounding in your recording room. This often isn't what is required for the track and a more 'produced sound might fit in much better with the music. The mike will also pick up any noises and rattles that might come from the instrument itself and depending on the positioning might even amplify the sound of the sax's keys rattling as they are pressed and the sound of the breathing of the player.

I once made a great sounding cello recording with two condenser mikes...  a beautiful, wooden, authentic stereo sound...   if you closed your eyes it was just like you were there with someone playing the cello right in front of you...  however, the moment of pride in having made a great recording was shattered when an intermittent loud hissing was heard...  it was the sound of the musician breathing through his nose...   every breath and grunt the player made had been recorded as clearly as the actual instrument itself. The performance had to be repeated and the mikes placed lower down and further away from the face.

Condenser mikes can also distort when the sound level is too high for the diaphragm. This distortion can heard but not seen on any of the Vu meters in the recording process. The signal that arrives at your mixing desk or your computer will apparently be within limits and not overloaded but the sound will still be distorted. This is the distortion of the microphone itself (this only happens with condenser mikes). A lot of condenser mikes have filters on them to cut the input level by 10db or 20db which are to be employed when using these mikes with loud sounding instruments. If the mike doesn't have a level cut filter then the only way around the problem is to move the mike further away from the sound source (which will change the sound) or change the mike.

Condenser mikes can work well with all instruments, there is no real rule for this... they seem to be favored when recording vocals, percussion effects, quiet acoustic instruments such as sitar, violin, lute etc., however as I already stated, there are no fixed rules concerning which microphone to use with which instrument.  

Dynamic mikes are more robust, they are suited in general to loud sounding instruments. It is impossible to distort a dynamic mike. They need to be placed quite close to the sound source, generally between 1 and 6 inches away. Any further and the mike still picks up the sound but looses all the bass frequencies giving a very thin and bodiless sound which is practically useless. Because they need to be so close to the source to pick up the sound and that sound needs to be fairly loud to start with they pick up very little of the 'room sound' I spoke of earlier. The sound they pick up is direct from the instrument and the reflected sound they pick up is of very low volume and lacking in body in comparison to the original sound. This can reproduce a sound from an instrument that doesn't sound exactly as our ears would hear that instrument if we were in the recording room. Going back to the example of the saxophone, when we use a dynamic mike we are getting the raw, raspy metal sound of the sax, with none or little of the sound of the room and as the sound of the sax is quite loud the sound of the keys in comparison doesn't appear to be picked up as much as if we were using a condenser mike.

In general  every single microphone colours the sound of the instrument somewhat. Even two identical mikes of the same make and model will sound a little different to one an other. The more expensive and precision condenser microphones all come with their individual frequency response graph (see fig1) generated by computer before leaving the factory. These graphs show frequency on one axes and decibels along the other. The line on the graph shows what frequencies are augmented or diminished for that particular mike...   just as if that particular equalisation curve had been applied to the natural sound being recorded.

Fig 1.

Microphone frequency response chart for a Sure Beta-57a dynamic mike.

You can see from the above example that this particular microphone naturally augments the upper frequencies around 5khz and 10khz this gives this mile its particular sound which might be described as anything from harsh to nasal tor even brilliant. This mike will in effect apply the above equalization curve to the natural sound (just as if you had used that eq on your mixing desk or computer).

You will also notice above that there are 4 different response curves based on approximate distance of the mike from the sound source. As I pointed out earlier..  the further away from the mike you are the less lower frequencies get picked up.

 Polar Response

Each microphone has its own particular polar response. That is to say the zone around the mike that picks up sound. There are four main polar response patterns to be found. these are illustrated in the diagrams below.

Cardioid Polar Response

This Pattern pick up sound from the front - 0º and does not pick up anything from behind the mike - 180º

It is the most common polar response especially amongst dynamic microphones.

Hypercardioid Polar Response

This pattern is similar to the Cardioid above but is more focused picking up less from the sides. It also has a small pick up area directly behind the mike (180º) which can often pick up reflected sound if placed close to a reflective surface.

Figure of Eight Polar Response

As the Graph clearly shows..  this pattern picks up sound equally from in frond as it does from behind with no sound being picked up from the sides.

Omni-directional Polar Response

Picks up sound equally from all directions.

It should be pointed out that although the above graphics are two dimensional, sound is three dimensional and the polar responses as outlined above are also really three dimensional. For example, the Figure of eight pattern is not so much an eight as two spheres, the omni directional not a circle but one sphere and the Cardioid not so much a heart shape but more like the form of an apple..

Most dynamic mikes have a Cardioid polar response. Most condenser mikes have a variable polar response with switches giving you a choice of patterns.

Useful Exercise.

A enlightening exercise is to set up a mike in your studio then go into the recording room with headphones on and hear exactly how that particular mike reacts. 

Try talking into it close up and slowly moving away to see exactly how the sound is affected by distance and exactly at what distance the difference is perceived. Also you can try moving around the mike to find its actual polar response..  see how and where the sound starts to fade or get thinner.

Once you have done this then try the exact same tests (preferably with the same mike stand in the same position) for a different mike. See the differences.

You can get to know all of the microphones in your arsenal in a very short time in this way.

If you have condenser mikes with multiple polar responses then you will not only notice the pick-up zones of each position but you will also see a slight coloring of the sound for each setting which will vary from mike to mile.

It is very important that you know exactly how each mike you are going to use in a recording is going to react  so you can position the musician and the mike accordingly.

Microphone Techniques

Mike choice and positioning for different instruments.

The following are only ideas meant as pointers and may not work in all situations. There are no rules in miking techniques except for use whatever sounds best and try not to have to use eq to get the sound you are looking for.

• Guitars
  • Amplifiers - Rock, Jazz,
  • Emulated amplifiers
  • Acoustic
  • Classical
  • Flamenco
    
• Bass Guitars
  
• Strings
  • Double Bass
  • Violin
  • Cello
    
• Brass
  • Trumpet
  • Trombone
  • *Sax
  • Tuba
  • Brass sections
    
• Woodwind
  • Sax
  • Clarinet
  • Flute
  • Oboe
    
• Percussion
  • Congas
  • Bongos
  • General small percussion and effects
    
• Drum kit
  • How to mike a drum kit
  • How to produce a drum kit

This is an excerpt from the book - Sound Engineering Basics by Andy Bramhill. 

Back to the top of Digital Audio Recording Tips