Threshold or Ratio: Which is more useful in a compressor?

[merlinb]

I am designing a two-knob compressor, and one knob will be output volume of course, but what should the other knob be?

I figured that attack and decay rarely get fiddled with, and most stompbox compressors don't include them as controls.

So that leaves threshold and compression ratio. Of those two, which do you think is more useful

[CynicalMan]

In some designs, such as the flatline or dod 280, changing the gain of the amplifier stage will change both ratio and threshold. IMO these offer a nice range of settings with one knob. If you can't do that, I'd go with threshold, although it's a close choice.

[Mark Hammer]

Think of it this way: which of those two would necessitate inclusion of a volume control more?  The answer is simple - threshold.