The modern recording studio is at the heart of the pop music industry. It is here that performers record, here that the sounds on radio, TV or hi-fi are prepared, processed and manufactured. The set-pieces of any recording studio are the tape machines and the mixing console - the desk from which the engineer controls the sound signals and the tape machines.
A typical mixing console might accommodate 24 inputs and 16 outputs. That is, 24 separate signals may be fed into the desk for processing from microphones, tape decks or even straight from the instruments ("direct injection") and these 24 signals can be fed to any, or between any or all of 16 output channels, which usually go straight to the tape machine. Clearly, if two or more inputs are switched or wired into one output, the signals will be mixed. Hence the title - mixing console or mixing desk.
Each of the separate channels will have volume and tone controls rather like sophisticated versions of those on a domestic record player, and often also preset level controls (level, in this context is virtually synonymous with volume). The pre-set controls are set at the beginning of a session, when the microphones or other input devices have been placed, tested and routed to their respective input channels. This leaves the other channel controls with a fine degree of adjustment over a relatively small range of volume between highest and lowest level.
A typical desk will also include metering facilities to measure incoming and outgoing signal strength, and comprehensive monitoring so that the signals can be listened to in the studio as they are being recorded. The monitoring systems will have its own amplifiers, which would be used to feed high quality speakers in the studio control room. It is usually possible to monitor the sound produced in the studio with control set tings different from those affecting the sound signals being recorded. This enables a producer to judge whether he should put the inputs through a different mix without commiting himself to a tape. A similar facility to monitoring, called fold back, allow the musician in the studio to monitor their own sound, sometimes in different - but simultaneous - mixes. There are also master faders on the desk which act as volume controls for the whole groups of input or output channels, reducing or increasing volume across the board.
The mixing console is essentially a system for routing signals through various different circuits into a tape machine. Tape machines are of the sync-head type, which use several heads stacked and independent switchable, so that any input can be simultaneously recorded with any other input on the same track which is being played back. This arrangement, first introduced by Ampex under the name Sel-Sync, is the basis of multi-tracking and over dubbing. Using a sync-head machine a single performer can fill all of the tape tracks with his own performances - taking one track at a time and playing to the accompaniment of the other tracks being played back and heard over the foldback. When all the tracks are laid down separately, they can be combined by feeding the play-back through the mixer, into a head that is recording over another track. This mixing and overdubbing process is known as reducing. Typically a reduction is two tracks mixed down from say, eight or sixteen tracks, so that the final two tracks have a stereo spread. The stereo spread is achieved by a de vice known as a pan-pot, which distributes a signal in a set ratio between the two stereo tracks.
There are more devices, linked into the mixing console, which help to avoid other troublesome noise. The Kepex Expander is widely used to automatically drop the recording level on a tape track when the signal itself drops below a certain level. For example, if a microphone is temporarily out of use and picking up a low level air conditioner hum, the Kepex will automatically drop the recording level so that the tape doesn't record the hum. When an instrument or vocal signal is again received in this microphone channel the recording level will be restored.
One other problem interferes in recording and especially in recording electric music. Very often the range of volume being recorded (the dynamic range) is too great for ordinary control settings to cope with. The human ear automatically compensates when it picks up rapid changes from high to low level signals or vice-versa, but this is a psychological mech anism that recording equipment doesn't have. Instead, if there is a sudden pack of volume it is most likely to cause unbearable distortion. or if there is a sudden drop in volume the quiet signal is liable to be lost in the dulge of sound that precedes it and follows it. The limiter/compresser solves this problem by "taming" the dynamic range of the incoming signals.
In effect, a limiter/compresser is an amplifier whose amplification decreases if the signal it is meant to amplify goes above a certain set level, and which automatically increases
the relative level of signals below a certain threshold. The result is that the sound seems to become denser, with no sudden peaks or drops in volume. This means that overloading distortion is highly unlikely, and that every part of the tape will be loud enough to hear, despite any passage too quiet to hear in the original material.
Photo and information by courtesy of Air Studios (No.2) & The Story of Pop.
|1 16-track recorder||11 4-track meters||21 ancillary group selectors|
|2 stereo recorder||12 24-track meters||22 ancillary panoramic potentiometers|
|3 24-track recorder||13 talk back microphones||23 microphone and line channel amplifiers and equal isers|
|4 portable limiters||14 group selectors||24 monitor echo control|
|5 jack field||15 fold back mixers||25 tape machine selectors|
|6 portable oscillator||16 group redirectors||26 studio playback selectors|
|7 Dolby M24 noise reduction units||17 panoramic potentiometers||27 monitor and foldback panel|
|8 monitor speakers||18 cue lights and talkback switches||28 echo send equaliser and echo plate remote control|
|9 control room/studio window||19 oscillator and ancillary meter||29 ancillary microphone and line channel amplifiers and equalisers|
|10 Limiter/compressors||20 echo return selectors||30 echo send and fold back send and prefade listen|
|31 monitor master fader|
|32 talkback buttons|
|33 monitor faders|
|34 echo return meters|
|35 echo return equalisers|
|36 ancillary echo send and foldback send and prefade listen|
|37 16-track tape machine remote|
|38 channel faders|
|39 group faders|
|40 quadrophonic fader|
|41 quadrophonic panoramic potentiometers|
|42 stereo panoramic potentiometers|
|43 24-track tape machine remote|