dsp::Compressor question

General JUCE discussion
#1

It looks like the juce compressor makes a step in gain when env hits the threshold (threshold = 0.5 and ratio = 2 for example).

// Ballistics filter with peak rectifier
auto env = envelopeFilter.processSample (channel, inputValue);

// VCA
auto gain = (env < threshold) ? static_cast<SampleType> (1.0)
                              : std::pow (env * thresholdInverse, ratioInverse - static_cast<SampleType> (1.0));

// Output
return gain * inputValue;

Can someone explain how this works and what I’m missing?

#2

I did a deep dive on this recently, what do you want to know, exactly?

Are you getting at it’s triggered by env, instead of straight up input, as you might expect?

#3

Thanks for the reply. I made a mistake when I plotted the function for verification. All ok now. It looks like this for threshold 0.5 and ratio 2:

image
image1514×970 117 KB

I wonder why we didn’t take a linear function. Is it because of decibels or because it should not cross zero?

Also, do you have an idea how we can make a smooth knee?

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