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Mix Amp Headroom
That Brand X mixer sounds OK at the music store when
the salesperson demos just two channels with a CD player. But then you
take the mixer home and connect all 16 channels to a pair of sizzlingly
high-output ADATs or DA-88s – when you start mixing down it sounds
like a Buick hitting a row of empty garbage cans. You're out of mix-amp
headroom.
Headroom– the ability to handle multiple, intense signals without
distortion – has always been what sets pro consoles apart from hobby
toys. Our mixers have headroom to spare, even when you've loaded every
channel with hot inputs. In fact, our compact mixers are the Number 1
choice of professional electronic percussionists for just that reason.
The bottleneck in any mixer is the mix amplifier, where
all signals come together. If it can't handle the full force of a dozen
or so simultaneous inputs plus aux returns, you hear some very gnarly distortion.
Basically, as more and more signals are summed together by a console mix
amp, its output level invariably rises toward the maximum operating level.
As you can see in the top figure, each time the number of input signals
is doubled, the output level goes up by as much as 3dB. It doesn't take
long to overload a conventional mix amp. And backing down the main faders
doesn't get you out of the red, since the bottleneck problem occurs before
this point.
All Mackie mixers have main mix amps that use our distinctive negative gain
mix amplifier architecture. Instead of mixing channels together at unity
gain where headroom is quickly exhausted, our mixers get more headroom by
mixing at -6dB (second figure). At this negative gain level, they
are capable of summing four times the number of hot signals before clipping
(last figure). That nets out at double the amount of mix amp headroom
available with many other compact mixers.
You'll notice the difference whether you're mixing keyboards, drums and
vocals live or mixing down digital multitrack recorder outputs in the studio. |
