Implement Converting Normalized LSFs to LPC Coefficients
From 4.2.7.5.6
This commit is contained in:
Sean DuBois
parent
b5ea7c4523
commit
733dc27100
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@ -1,8 +1,6 @@
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package silk
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import (
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"fmt"
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"github.com/pion/opus/internal/rangecoding"
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)
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@ -312,9 +310,9 @@ func (d *Decoder) normalizeLineSpectralFrequencyCoefficients(bandwidth Bandwidth
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// Let d_LPC be the order of the codebook, i.e., 10 for NB and MB, and 16 for WB
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dLPC := len(resQ10)
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nlsfQ15 = make([]int16, len(resQ10))
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w2Q18 := make([]uint, len(resQ10))
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wQ9 := make([]int16, len(resQ10))
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nlsfQ15 = make([]int16, dLPC)
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w2Q18 := make([]uint, dLPC)
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wQ9 := make([]int16, dLPC)
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cb1Q8 := codebookNormalizedLSFStageOneNarrowbandOrMediumband
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if bandwidth == BandwidthWideband {
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@ -412,8 +410,8 @@ func (d *Decoder) normalizeLSFInterpolation() error {
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return nil
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}
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func (d *Decoder) convertNormalizedLSFsToLPCCoefficients(I1 uint32, nlsfQ1 []int16, bandwidth Bandwidth) {
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cQ17 := make([]int32, len(nlsfQ1))
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func (d *Decoder) convertNormalizedLSFsToLPCCoefficients(nlsfQ15 []int16, bandwidth Bandwidth) (a32Q17 []int32) {
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cQ17 := make([]int32, len(nlsfQ15))
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cosQ12 := q12CosineTableForLSFConverion
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ordering := lsfOrderingForPolynomialEvaluationNarrowbandAndMediumband
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@ -435,19 +433,21 @@ func (d *Decoder) convertNormalizedLSFsToLPCCoefficients(I1 uint32, nlsfQ1 []int
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// i'th entry of Table 28.
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.6
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for k := range nlsfQ1 {
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i := int32(nlsfQ1[k] >> 8)
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f := int32(nlsfQ1[k] & 255)
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for k := range nlsfQ15 {
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i := int32(nlsfQ15[k] >> 8)
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f := int32(nlsfQ15[k] & 255)
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cQ17[ordering[k]] = (cosQ12[i]*256 +
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(cosQ12[i+1]-cosQ12[i])*f + 4) >> 3
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}
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// Given the list of cosine values, silk_NLSF2A_find_poly() (NLSF2A.c)
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// computes the coefficients of P and Q, described here via a simple
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// recurrence. Let p_Q16[k][j] and q_Q16[k][j] be the coefficients of
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// the products of the first (k+1) root pairs for P and Q, with j
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// indexing the coefficient number. Only the first (k+2) coefficients
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pQ16 := make([]int32, (len(nlsfQ15)/2)+1)
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qQ16 := make([]int32, (len(nlsfQ15)/2)+1)
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// Given the list of cosine values compute the coefficients of P and Q,
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// described here via a simple recurrence. Let p_Q16[k][j] and q_Q16[k][j]
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// be the coefficients of the products of the first (k+1) root pairs for P and
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// Q, with j indexing the coefficient number. Only the first (k+2) coefficients
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// are needed, as the products are symmetric. Let
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//
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// p_Q16[0][0] = q_Q16[0][0] = 1<<16
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@ -455,6 +455,15 @@ func (d *Decoder) convertNormalizedLSFsToLPCCoefficients(I1 uint32, nlsfQ1 []int
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// q_Q16[0][1] = -c_Q17[1]
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// d2 = d_LPC/2
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.6
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pQ16[0] = 1 << 16
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qQ16[0] = 1 << 16
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pQ16[1] = -cQ17[0]
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qQ16[1] = -cQ17[1]
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dLPC := len(nlsfQ15)
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d2 := dLPC / 2
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// As boundary conditions, assume p_Q16[k][j] = q_Q16[k][j] = 0 for all j < 0.
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// Also, assume (because of the symmetry)
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//
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@ -462,15 +471,51 @@ func (d *Decoder) convertNormalizedLSFsToLPCCoefficients(I1 uint32, nlsfQ1 []int
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// q_Q16[k][k+2] = q_Q16[k][k]
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//
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// Then, for 0 < k < d2 and 0 <= j <= k+1,
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//
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// p_Q16[k][j] = p_Q16[k-1][j] + p_Q16[k-1][j-2]
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// - ((c_Q17[2*k]*p_Q16[k-1][j-1] + 32768)>>16)
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//
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// q_Q16[k][j] = q_Q16[k-1][j] + q_Q16[k-1][j-2]
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// - ((c_Q17[2*k+1]*q_Q16[k-1][j-1] + 32768)>>16)
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.6
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fmt.Println(cQ17)
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panic("")
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for k := 1; k < d2; k++ {
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pQ16[k+1] = pQ16[k-1]*2 - int32(((int64(cQ17[2*k])*int64(pQ16[k]))+32768)>>16)
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qQ16[k+1] = qQ16[k-1]*2 - int32(((int64(cQ17[(2*k)+1])*int64(qQ16[k]))+32768)>>16)
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for j := k; j > 1; j-- {
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pQ16[j] += pQ16[j-2] - int32(((int64(cQ17[2*k])*int64(pQ16[j-1]))+32768)>>16)
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qQ16[j] += qQ16[j-2] - int32(((int64(cQ17[(2*k)+1])*int64(qQ16[j-1]))+32768)>>16)
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}
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pQ16[1] -= cQ17[2*k]
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qQ16[1] -= cQ17[2*k+1]
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}
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// silk_NLSF2A() uses the values from the last row of this recurrence to
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// reconstruct a 32-bit version of the LPC filter (without the leading
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// 1.0 coefficient), a32_Q17[k], 0 <= k < d2:
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//
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// a32_Q17[k] = -(q_Q16[d2-1][k+1] - q_Q16[d2-1][k])
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// - (p_Q16[d2-1][k+1] + p_Q16[d2-1][k]))
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//
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// a32_Q17[d_LPC-k-1] = (q_Q16[d2-1][k+1] - q_Q16[d2-1][k])
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// - (p_Q16[d2-1][k+1] + p_Q16[d2-1][k]))
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//
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// The sum and difference of two terms from each of the p_Q16 and q_Q16
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// coefficient lists reflect the (1 + z**-1) and (1 - z**-1) factors of
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// P and Q, respectively. The promotion of the expression from Q16 to
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// Q17 implicitly scales the result by 1/2.
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//
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.6
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a32Q17 = make([]int32, len(nlsfQ15))
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for k := 0; k < d2; k++ {
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a32Q17[k] = -(qQ16[k+1] - qQ16[k]) - (pQ16[k+1] + pQ16[k])
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a32Q17[dLPC-k-1] = (qQ16[k+1] - qQ16[k]) - (pQ16[k+1] + pQ16[k])
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}
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return
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}
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// As described in Section 4.2.7.8.6, SILK uses a Linear Congruential
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@ -959,7 +1004,7 @@ func (d *Decoder) Decode(in []byte, isStereo bool, nanoseconds int, bandwidth Ba
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resQ10 := d.normalizeLineSpectralFrequencyStageTwo(bandwidth, I1)
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.3
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nlsfQ1 := d.normalizeLineSpectralFrequencyCoefficients(bandwidth, resQ10, I1)
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nlsfQ15 := d.normalizeLineSpectralFrequencyCoefficients(bandwidth, resQ10, I1)
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.4
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d.normalizeLSFStabilization()
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@ -970,7 +1015,7 @@ func (d *Decoder) Decode(in []byte, isStereo bool, nanoseconds int, bandwidth Ba
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}
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// https://datatracker.ietf.org/doc/html/rfc6716#section-4.2.7.5.6
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d.convertNormalizedLSFsToLPCCoefficients(I1, nlsfQ1, bandwidth)
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d.convertNormalizedLSFsToLPCCoefficients(nlsfQ15, bandwidth)
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return
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}
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@ -98,6 +98,25 @@ func TestNormalizeLineSpectralFrequencyCoefficients(t *testing.T) {
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}
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}
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func TestConvertNormalizedLSFsToLPCCoefficients(t *testing.T) {
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d := &Decoder{}
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nlsfQ15 := []int16{
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0x854, 0xe00, 0x1580, 0x1d00, 0x2500, 0x2c80, 0x3480,
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0x3c00, 0x4380, 0x4b00, 0x5280, 0x5a00, 0x6200, 0x6980,
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0x7100, 0x7880,
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}
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expectedA32Q17 := []int32{
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12974, 9765, 4176, 3646, -3766, -4429, -2292, -4663,
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-3441, -3848, -4493, -1614, -1960, -3112, -2153, -2898,
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}
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if !reflect.DeepEqual(d.convertNormalizedLSFsToLPCCoefficients(nlsfQ15, BandwidthWideband), expectedA32Q17) {
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t.Fatal()
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}
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}
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func TestExcitation(t *testing.T) {
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expected := []int32{
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25, -25, -25, -25, 25, 25, -25, 25, 25, -25, 25, -25, -25, -25, 25, 25, -25,
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