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https://github.com/vsariola/sointu.git
synced 2025-05-28 03:10:24 -04:00
38e9007bf8
Throughout sointu, we assume stereo audiobuffers, but were passing around []float32. This had several issues, including len(buf)/2 and numSamples*2 type of length conversion in many places. Also, it caused one bug in a test case, causing it to succeed when it should have not (the test had +-1 when it should have had +-2). This refactoring makes it impossible to have odd length buffer issues.
61 lines
1.8 KiB
Go
61 lines
1.8 KiB
Go
package tracker
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import (
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"errors"
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"math"
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"github.com/vsariola/sointu"
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)
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// Volume represents an average and peak volume measurement, in decibels. 0 dB =
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// signal level of +-1.
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type Volume struct {
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Average [2]float64
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Peak [2]float64
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}
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// Analyze updates Average and Peak fields, by analyzing the given buffer.
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//
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// Internally, it first converts the signal to decibels (0 dB = +-1). Then, the
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// average volume level is computed by smoothing the decibel values with a
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// exponentially decaying average, with a time constant tau (in seconds).
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// Typical value could be 0.3 (seconds).
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//
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// Peak volume detection is similar exponential smoothing, but the time
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// constants for attack and release are different. Generally attack << release.
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// Typical values could be attack 1.5e-3 and release 1.5 (seconds)
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//
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// minVolume and maxVolume are hard limits in decibels to prevent negative
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// infinities for volumes
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func (v *Volume) Analyze(buffer sointu.AudioBuffer, tau float64, attack float64, release float64, minVolume float64, maxVolume float64) error {
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alpha := 1 - math.Exp(-1.0/(tau*44100)) // from https://en.wikipedia.org/wiki/Exponential_smoothing
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alphaAttack := 1 - math.Exp(-1.0/(attack*44100))
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alphaRelease := 1 - math.Exp(-1.0/(release*44100))
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var err error
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for j := 0; j < 2; j++ {
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for i := 0; i < len(buffer); i++ {
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sample2 := float64(buffer[i][j] * buffer[i][j])
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if math.IsNaN(sample2) {
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if err == nil {
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err = errors.New("NaN detected in master output")
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}
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continue
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}
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dB := 10 * math.Log10(float64(sample2))
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if dB < minVolume || math.IsNaN(dB) {
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dB = minVolume
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}
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if dB > maxVolume {
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dB = maxVolume
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}
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v.Average[j] += (dB - v.Average[j]) * alpha
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alphaPeak := alphaAttack
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if dB < v.Peak[j] {
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alphaPeak = alphaRelease
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}
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v.Peak[j] += (dB - v.Peak[j]) * alphaPeak
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}
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}
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return err
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}
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