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Fix AudioStream cubic resampling #51082

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merged 2 commits into from
Aug 6, 2021
Merged

Fix AudioStream cubic resampling #51082

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57ccfab
Revert "Implement a new resampling algorithm in AudioStreamPlaybackRe…
ellenhp Jul 30, 2021
2d450c6
Fix Godot's cubic resampling algorithm
ellenhp Jul 30, 2021
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18 changes: 9 additions & 9 deletions servers/audio/audio_stream.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -54,21 +54,21 @@ void AudioStreamPlaybackResampled::mix(AudioFrame *p_buffer, float p_rate_scale,

for (int i = 0; i < p_frames; i++) {
uint32_t idx = CUBIC_INTERP_HISTORY + uint32_t(mix_offset >> FP_BITS);
// 4 point, 4th order optimal resampling algorithm from: http://yehar.com/blog/wp-content/uploads/2009/08/deip.pdf
//standard cubic interpolation (great quality/performance ratio)
//this used to be moved to a LUT for greater performance, but nowadays CPU speed is generally faster than memory.
float mu = (mix_offset & FP_MASK) / float(FP_LEN);
AudioFrame y0 = internal_buffer[idx - 3];
AudioFrame y1 = internal_buffer[idx - 2];
AudioFrame y2 = internal_buffer[idx - 1];
AudioFrame y3 = internal_buffer[idx - 0];

AudioFrame even1 = y2 + y1, odd1 = y2 - y1;
AudioFrame even2 = y3 + y0, odd2 = y3 - y0;
AudioFrame c0 = even1 * 0.46835497211269561 + even2 * 0.03164502784253309;
AudioFrame c1 = odd1 * 0.56001293337091440 + odd2 * 0.14666238593949288;
AudioFrame c2 = even1 * -0.250038759826233691 + even2 * 0.25003876124297131;
AudioFrame c3 = odd1 * -0.49949850957839148 + odd2 * 0.16649935475113800;
AudioFrame c4 = even1 * 0.00016095224137360 + even2 * -0.00016095810460478;
p_buffer[i] = (((c4 * mu + c3) * mu + c2) * mu + c1) * mu + c0;
float mu2 = mu * mu;
AudioFrame a0 = 3 * y1 - 3 * y2 + y3 - y0;
AudioFrame a1 = 2 * y0 - 5 * y1 + 4 * y2 - y3;
AudioFrame a2 = y2 - y0;
AudioFrame a3 = 2 * y1;

p_buffer[i] = (a0 * mu * mu2 + a1 * mu2 + a2 * mu + a3) / 2;

mix_offset += mix_increment;

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