very simple compressor module question

[Fozzie]

I have wondered a long time what the "ref lvl" knob on the compressor module (both NM and G2) does exactly, so it's time to put the question here. The manual says that it's the level that the sound is compressed to. But this doesn't make sense to me, as the threshold sets the eh well... threshold , and the ratio the amount of compression. Therefore the description in the manual doesn't describe anything that's not already taken care of by the other knobs imho.
Of course I can hear that the signal gets louder if you turn it up, but is it really just makeup gain? I have never seen a compressor with a knob called reference level, but then again, I haven't seen many (hardware) compressors. If it is makeup gain, why not call it gain or makeup gain?

Anyone?

[jksuperstar]

The naming is kinda funny, but it may be more accurate.

The act of "compression" is taking 1 dynamic range (in the nord that's 22 bits I think), and squeezing it down into another. If it's squeezed down (to say 16bits), you are no longer using the full bit-width of the red signal, and your wasting your dynamics, or bit resolution. This method is used in the analog world, but there you have (in theory) infinite resolution, so you just "gain" up the signal to get it back up to a proper level (or for effect) for output to other gear (you called it "makeup gain").

However, if you just compress a signal down in the digital world, and you loose those lower bits of information, they will never be found again! If you then just added a gain stage, the signal would be louder, but the lower bits, your real resolution, would still be gone. So Clavia may have done something clever to keep from loosing those bits, and calling the output a "gain" would not accurately describe what's going on inside the module. Just my 2 cents based on other DSP experience. My guess is that Clavia actually "gains up" the signal to a full 24-bits *before* the compression, then divides it down before the output, which is where it needs a reference level to translate to, rather than a simple gain measurement.

Of course, they might just call it "Reference Level" because they wanted to.

[Fozzie]

Thanks JKsuperstar, that's an interesting thought. I am very interested in dsp theory (as a beginning amateur), and doing some reading here and there. However, I had never thought of compression on analog vs digital signals that way, so even if your theory about the knob name is incorrect, I like it!