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Add soft-knee downwards compression

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Robbert van der Helm 2022-07-24 15:58:30 +02:00
parent 08201d2a87
commit 068549607d
1 changed files with 25 additions and 5 deletions
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30
plugins/spectral_compressor/src/compressor_bank.rs
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@ -546,19 +546,39 @@ impl CompressorBank {
// All compression happens in the linear domain to save a logarithm // All compression happens in the linear domain to save a logarithm
if *downwards_ratio_recip != 1.0 { if *downwards_ratio_recip != 1.0 {
// TODO: We need the knee starts and ends on this struct // The soft-knee option will fade in the compression curve when reaching the knee
// TODO: As mentioned above, soft knee, replace the threshold // start until it mtaches the hard-knee curve at the knee-end
if envelope > downwards_threshold { if envelope >= downwards_knee_end {
// Because we're working in the linear domain, we care about the ratio between // Because we're working in the linear domain, we care about the ratio between
// the threshold and the envelope's current value. And log-space division // the threshold and the envelope's current value. And log-space division
// becomes linear-space exponentiation by the reciprocal, or taking the nth // becomes linear-space exponentiation by the reciprocal, or taking the nth
// root. // root.
let threshold_ratio = *envelope / *downwards_threshold; let threshold_ratio = envelope / downwards_threshold;
scale /= threshold_ratio / threshold_ratio.powf(*downwards_ratio_recip); scale /= threshold_ratio / threshold_ratio.powf(*downwards_ratio_recip);
} else if envelope >= downwards_knee_start {
// When the knee width is set to 0 dB, `downwards_knee_start ==
// downwards_knee_end` and this branch is never hit
let linear_knee_width = downwards_knee_end - downwards_knee_start;
let raw_knee_t = (envelope - downwards_knee_start) / linear_knee_width;
nih_debug_assert!((0.0..=1.0).contains(&raw_knee_t));
// TODO: Apart from a small discontinuety in the derivative/slope at the start
// of the knee this equation does exaclty what you'd expect it to, but it
// feels a bit weird. Should probably look for a cleaner way to calculate
// this soft knee in linear-space at some point.
let knee_t = (1.0 - raw_knee_t).powf(downwards_knee_scaling_factor);
nih_debug_assert!((0.0..=1.0).contains(&knee_t));
// We'll linearly interpolate between compression at the knee start and at the
// actual threshold based on `knee_t`
let knee_ratio = envelope / downwards_knee_start;
let threshold_ratio = envelope / downwards_threshold;
scale /= (knee_t * (knee_ratio / knee_ratio.powf(*downwards_ratio_recip)))
+ ((1.0 - knee_t)
* (threshold_ratio / threshold_ratio.powf(*downwards_ratio_recip)));
} }
} }
// TODO: More stuff
// TODO: Upwards compression // TODO: Upwards compression
*bin *= scale; *bin *= scale;