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audio/internal/convert: Fix algorithm

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This commit is contained in:
Hajime Hoshi 2018-01-05 17:39:47 +09:00
parent 4bcb2e5682
commit 2884fb7070
1 changed files with 11 additions and 10 deletions
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21
audio/internal/convert/resampling.go
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@ -22,7 +22,7 @@ import (
)
func sinc(x float64) float64 {
if x == 0 {
if math.Abs(x) < 1e-8 {
return 1
}
return math.Sin(x) / x
@ -128,26 +128,27 @@ func (r *Resampling) src(i int) (float64, float64, error) {
func (r *Resampling) at(t int64) (float64, float64, error) {
windowSize := 4.0
tInSrc := float64(t) * float64(r.from) / float64(r.to)
startN := tInSrc - windowSize
startN := int64(tInSrc - windowSize)
if startN < 0 {
startN = 0
}
if float64(r.size/4) <= startN {
startN = float64(r.size/4) - 1
if r.size/4 <= startN {
startN = r.size/4 - 1
}
endN := tInSrc + windowSize + 1
if float64(r.size/4) <= endN {
endN = float64(r.size/4) - 1
endN := int64(tInSrc + windowSize)
if r.size/4 <= endN {
endN = r.size/4 - 1
}
lv := 0.0
rv := 0.0
for n := startN; n < endN; n++ {
for n := startN; n <= endN; n++ {
srcL, srcR, err := r.src(int(n))
if err != nil {
return 0, 0, err
}
w := 0.5 + 0.5*math.Cos(2*math.Pi*(tInSrc-n)/(windowSize*2+1))
s := sinc(math.Pi*(tInSrc-n)) * w
d := tInSrc - float64(n)
w := 0.5 + 0.5*math.Cos(2*math.Pi*d/(windowSize*2+1))
s := sinc(math.Pi*d) * w
lv += srcL * s
rv += srcR * s
}