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first set of basic transforms
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‎LICENSE

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Apache License
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‎bit_crush.go

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package transforms
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import (
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"math"
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"github.com/go-audio/audio"
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)
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var (
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crusherStepSize = 0.000001
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CrusherMinFactor = 1.0
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CrusherMaxFactor = 2097152.0
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)
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// BitCrush reduces the resolution of the sample to the target bit depth
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// Note that bit crusher effects are usually made of this feature + a decimator
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func BitCrush(buf *audio.FloatBuffer, factor float64) {
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stepSize := crusherStepSize * factor
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for i := 0; i < len(buf.Data); i++ {
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frac, exp := math.Frexp(buf.Data[i])
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frac = signum(frac) * math.Floor(math.Abs(frac)/stepSize+0.5) * stepSize
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buf.Data[i] = math.Ldexp(frac, exp)
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}
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}
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func signum(v float64) float64 {
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if v >= 0.0 {
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return 1.0
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}
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return -1.0
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}

‎mono.go

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package transforms
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import "github.com/go-audio/audio"
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// MonoDownmix converts the buffer to a mono buffer
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// by downmixing the channels together.
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func MonoDownmix(buf *audio.FloatBuffer) error {
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if buf == nil || buf.Format == nil {
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return audio.ErrInvalidBuffer
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}
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if buf.Format == nil {
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return audio.ErrInvalidBuffer
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}
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nChans := buf.Format.NumChannels
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if nChans < 2 {
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return nil
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}
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nChansF := float64(nChans)
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frameCount := len(buf.Data) / buf.Format.NumChannels
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newData := make([]float64, frameCount)
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for i := 0; i < frameCount; i++ {
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newData[i] = 0
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for j := 0; j < nChans; j++ {
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newData[i] += buf.Data[i*nChans+j]
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}
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newData[i] /= nChansF
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}
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buf.Data = newData
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buf.Format.NumChannels = 1
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return nil
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}

‎normalize.go

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package transforms
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import (
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"math"
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"github.com/go-audio/audio"
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)
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// NormalizeMax sets the max value to 1 and normalize the rest of the data.
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func NormalizeMax(buf *audio.FloatBuffer) {
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if buf == nil {
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return
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}
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max := 0.0
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for i := 0; i < len(buf.Data); i++ {
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if math.Abs(buf.Data[i]) > max {
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max = math.Abs(buf.Data[i])
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}
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}
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if max != 0.0 {
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for i := 0; i < len(buf.Data); i++ {
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buf.Data[i] /= max
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}
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}
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}

‎pcm_scale.go

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package transforms
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import "github.com/go-audio/audio"
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// PCMScale converts a buffer with audio content from -1 to 1 into
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// the PCM scale based on the buffer's bitdepth.
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// Note that while the PCM data is scaled, the PCM format is not changed.
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func PCMScale(buf *audio.FloatBuffer) error {
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if buf == nil || buf.Format == nil {
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return audio.ErrInvalidBuffer
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}
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factor := float64(audio.IntMaxSignedValue(buf.Format.BitDepth))
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for i := 0; i < len(buf.Data); i++ {
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buf.Data[i] *= factor
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}
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return nil
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}

‎quantize.go

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package transforms
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import (
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"math"
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"github.com/go-audio/audio"
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)
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// Quantize quantizes the audio signal to match the target bitDepth
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func Quantize(buf *audio.FloatBuffer, bitDepth int) {
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if buf == nil {
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return
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}
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max := math.Pow(2, float64(bitDepth)) - 1
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bufLen := len(buf.Data)
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for i := 0; i < bufLen; i++ {
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buf.Data[i] = round((buf.Data[i]+1)*max)/max - 1.0
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}
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}
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func round(f float64) float64 {
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if f > 0.0 {
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return math.Floor(f + 0.5)
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}
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return math.Ceil(f - 0.5)
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}

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