Digital hardware compressors for tracking - impossible?

[Matt Hepworth]

So, all these digital hardware compressors - some intended for live sound and some for studio. Are they using something clever to prevent clipping of their AD before it hits their compression algorithms? I just can't see these working.

Take the Mackie Quad Comp/Gate for example. Intended for live sound situations it seems, but I simply can't see how a compressor like this would do anything against potential overs in your signal that would clip its ADC. Are they shifting the dynamic range so the lowest bits are truncated in order to gain extra headroom or something along those lines?

Am I missing something here?

[Matt Hepworth]

Here's what I'm referring to
Mackie - QUAD Gate/Compression

Comments?

[dannygold]

Interesting question... I never thought of that. PURE speculation here, but if I was designing such a box I'd just attenuate the hell out of the signal in the analog domain because at 24 bits it's hard to reach the floor of quanitzation noise but easy to overload. Then to be safe I'd put a limiter pre A/D... but again I'd have knocked the signal down so much the limiter would be just a safety.

[Matt Hepworth]

Yeah, I suppose some kind of limiter IC and a 20dB attenuator at the input could be a way it's done. I sure would like to know, though, whether there's any better way that they might be doing it.

[jcatena]

Using a digital compressor for tracking makes not sense at all (the input of such a compressor is an ADC anyway).
Furthermore, with high end 24 bits ADCs, no analog compressor is needed, as the dynamic range is large enough.
All you want is to adjust the input level to assure it doesn't clip. With a DNR of 115 dB or more you don't even need to set very close to 0 dBFS. Even if the peaks are -10dB FS, the resulting SNR is better than any analog signal you can send to it, so an analog compressor can only degrade it.
After it is recorded, use any compression you need for mixing and mastering, digital if you want it clean, analog if you appreciate the colour of your analog compressor and don't worry much about the added noise.