From 068549607d2a7c81b8f91e98e4c4d27daec9bf0e Mon Sep 17 00:00:00 2001 From: Robbert van der Helm Date: Sun, 24 Jul 2022 15:58:30 +0200 Subject: [PATCH] Add soft-knee downwards compression --- .../src/compressor_bank.rs | 30 +++++++++++++++---- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/plugins/spectral_compressor/src/compressor_bank.rs b/plugins/spectral_compressor/src/compressor_bank.rs index 01e0b646..722ce7e0 100644 --- a/plugins/spectral_compressor/src/compressor_bank.rs +++ b/plugins/spectral_compressor/src/compressor_bank.rs @@ -546,19 +546,39 @@ impl CompressorBank { // All compression happens in the linear domain to save a logarithm if *downwards_ratio_recip != 1.0 { - // TODO: We need the knee starts and ends on this struct - // TODO: As mentioned above, soft knee, replace the threshold - if envelope > downwards_threshold { + // The soft-knee option will fade in the compression curve when reaching the knee + // start until it mtaches the hard-knee curve at the knee-end + if envelope >= downwards_knee_end { // 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 // becomes linear-space exponentiation by the reciprocal, or taking the nth // root. - let threshold_ratio = *envelope / *downwards_threshold; + let threshold_ratio = envelope / downwards_threshold; 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 *bin *= scale;