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Use LPC values from previous when current frame has no cached values

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This commit is contained in:
Sean DuBois 2022-09-25 22:42:19 -04:00
parent 238ccbfc34
commit 684adce144
1 changed files with 25 additions and 1 deletions
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26
internal/silk/decoder.go
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@ -17,6 +17,12 @@ type Decoder struct {
previousLogGain int32
// The decoder saves the final d_LPC values, i.e., lpc[i] such that
// (j + n - d_LPC) <= i < (j + n), to feed into the LPC synthesis of the
// next subframe. This requires storage for up to 16 values of lpc[i]
// (for WB frames).
previousFrameLPCValues []float32
// This requires storage to buffer up to 306 values of out[i] from
// previous subframes.
// https://www.rfc-editor.org/rfc/rfc6716#section-4.2.7.9.1
@ -1521,6 +1527,8 @@ func (d *Decoder) lpcSynthesis(out []float32, bandwidth Bandwidth, n, s, dLPC in
for k := 0; k < dLPC; k++ {
if lpcIndex := sampleIndex - k - 1; lpcIndex >= 0 {
currentLPCVal = lpc[lpcIndex]
} else if i < len(d.previousFrameLPCValues) && s == 0 {
currentLPCVal = d.previousFrameLPCValues[len(d.previousFrameLPCValues)-1+(i-k)]
} else {
currentLPCVal = 0
}
@ -1535,6 +1543,14 @@ func (d *Decoder) lpcSynthesis(out []float32, bandwidth Bandwidth, n, s, dLPC in
// out[i] = clamp(-1.0, lpc[i], 1.0)
//
out[i] = clampFloat(-1.0, lpc[sampleIndex], 1.0)
// The decoder saves the final d_LPC values, i.e., lpc[i] such that
// (j + n - d_LPC) <= i < (j + n), to feed into the LPC synthesis of the
// next subframe. This requires storage for up to 16 values of lpc[i]
// (for WB frames).
if len(out)-1 == i && d.haveDecoded {
d.previousFrameLPCValues = append([]float32{}, lpc[len(lpc)-dLPC:]...)
}
d.finalOutValues[len(d.finalOutValues)-n+i] = out[i]
}
}
@ -1609,7 +1625,15 @@ func (d *Decoder) silkFrameReconstruction(
//
// https://www.rfc-editor.org/rfc/rfc6716.html#section-4.2.7.9.1
if signalType == frameSignalTypeVoiced {
d.ltpSynthesis(out, signalType, bQ7, pitchLags, eQ23, n, j, s, dLPC, LTPscaleQ14, bandwidth, wQ2, aQ12[aQ12Index], gainQ16, lpc, res, resLag)
d.ltpSynthesis(
out,
signalType,
bQ7, pitchLags,
eQ23, n, j, s, dLPC,
LTPscaleQ14, bandwidth,
wQ2,
aQ12[aQ12Index], gainQ16, lpc, res, resLag,
)
}
//https://www.rfc-editor.org/rfc/rfc6716.html#section-4.2.7.9.2