The specs for the web audio API dynamic compressor node refer to some curve being drawn over various decibel values. How can I visualize that curve?
For filter nodes, the web audio API provides a getFrequencyResponse method that produces data that can be visualized on a 2D canvas.
Is there a similar method for the dynamic processor node? Or are there well-known formulas used to compute the magnitude of the node's effect on various dB values?
I'm not sure exactly how to calculate the curve for knee, but I'm pretty sure it shouldn't be super difficult. Ignoring the knee, here's what you'd need:
First, you'd start out with a line that has a slope of 1 (45 degree angle, up and to the right). Another way of saying that is that output = input
Then, when you hit threshold, you change the slope of the line to match your compression ratio. So if your ratio is 2.3:1, your slope above the threshold would be output = input / 2.3.
Anyway, I'm sure if you do some searching, you can figure out how to factor in the knee. It's probably just a parabola that joins the two slopes (with a vertex at the point where they would normally intersect if the knee was 0). Then you just need to figure out what the value does, but if you read the Web Audio spec, the unit for knee is dB – which leads me to believe this isn't really implementation-specific. I think there probably is a Right Way™ to do it.