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Why do microphone preamplifiers come in sets of eight?

Microphone preamplifiers, if they are not single-channel, always seem to come in sets of eight channels. But if you had a ten-channel mic pre, how much more could you do with it?


What is it with the number eight? Everything in audio seems to come in multiples of eight - microphone preamplifiers, mixing console channels, multicore cables, wall box XLR sockets, patchbay rows... nearly always they are supplied in multiples of eight. Odd when we have ten fingers and therefore count in tens.

This is particularly odd in the case of microphone preamplifiers...

So you buy your eight channel mic pre - what's the biggest job you are likely to use it on?

That's right - recording a drum kit. If you wanted to record a full orchestra then you would have bought an entire mixing console.

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The bog-standard configuration of the drum kit has five drums, two cymbals and a hihat. Maybe a cowbell too, but we'll forget about that for the moment. And maybe Lars has a bigger kit, but then he would, wouldn't he. (I'd say how many drums he has but Metallica would probably sue me for using a number they think they own the copyright on).

The current style of recording drums requires one microphone per drum, so that's five. Then the hihat needs one to give it sparkle. And of course the two overheads to catch the overall kit sound in stereo.

So 5 + 1 + 2 = 8... everything fine!

Well actually not so fine. What about putting a mic under the snare drum to capture the rattle of the snare wires? This is a subtle sound, and believe it or not it is possible to play the drums with a subtlety that is often unfortunately lost in the melee. (Don't forget that you'll need to invert the phase of this mic otherwise the snare drum will sound distinctly odd).

But 8 + 1 = 9. Now we have one too many mics for our mic preamp.

So it's probably time that we counted our fingers and set ten as the standard multiple of mic preamps and everything else. This would give enough inputs for an entire conventional drum kit, fully miked. And it would allow on additional input for a guide track, guitar perhaps, to be recorded along with the drums.

10-channel microphone preamplifiers. Exactly what we need!

By David Mellor Sunday February 27, 2011