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obs-filters: Ensure gain is positive for upward compressor

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The gain should be positive for an upward compressor. Initially, the
gain would be zeroe'd below -60 dB to ensure noise is not amplified by
the upward compressor. This created a discontinuity at -60 dB since
just above -60 dB, the audio is boosted by +20 dB (at default
settings). This was fixed in commit 50db097 which decreased smoothly
the gain so that it's 0 dB at -60 dB. However that commit forgot to
limit the gain decrease which was negative below -60 dB.
This is fixed by the current commit.
Additionally initialization allowed -inf gain. We hard limit to positive
gains only as they should be for an upward compressor.
The bugfix was found by R1ch and put in form by pkv.

Co-authored-by: pkv <pkv@obsproject.com>
Signed-off-by: pkv <pkv@obsproject.com>
This commit is contained in:
R1CH
2023-02-04 08:27:15 +01:00
committed by Jim
parent e9a401d898
commit c36583d794
1 changed files with 5 additions and 2 deletions
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7
plugins/obs-filters/expander-filter.c
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@@ -360,12 +360,15 @@ static inline void process_sample(size_t idx, float *samples, float *env_buf,
float diff = threshold - env_db;
if (is_upwcomp && env_db <= (threshold - 60.0f) / 2)
diff = env_db + 60.0f;
diff = env_db + 60.0f > 0 ? env_db + 60.0f : 0.0f;
float gain = 0.0f;
float prev_gain = 0.0f;
// Note that the gain is always >= 0 for the upward compressor
// but is always <=0 for the expander.
if (is_upwcomp) {
prev_gain = idx > 0 ? fmaxf(gain_db[idx - 1], 0)
: fmaxf(channel_gain, 0);
// gain above knee (included for clarity):
if (env_db >= threshold + knee / 2)
gain = 0.0f;
@@ -377,9 +380,9 @@ static inline void process_sample(size_t idx, float *samples, float *env_buf,
threshold + knee / 2 > env_db)
gain = slope * powf(diff + knee / 2, 2) / (2.0f * knee);
} else {
prev_gain = idx > 0 ? gain_db[idx - 1] : channel_gain;
gain = diff > 0.0f ? fmaxf(slope * diff, -60.0f) : 0.0f;
}
float prev_gain = idx > 0 ? gain_db[idx - 1] : channel_gain;
/* --------------------------------- */
/* ballistics (attack/release) */