lsp2.c

symbian 系统下的g.723 g.723_24实现, 本源码在 series60 sdk fp2下调试通过

            LspQntPnt += BandInfoTable[k][1];

            if (Err > Max)
            {
                Max = Err;
                Indx = (Word32) i;
            }
        }
        Rez = (Rez << 8) | Indx;
    }

    return Rez;
}


/*
**
** Function:            Lsp_Inq()
**
** Description:     Performs inverse vector quantization of the
**          LSP frequencies.  The LSP vector is divided
**          into 3 sub-vectors, or bands, of dimension 3,
**          3, and 4.  Each band is inverse quantized
**          separately using a different VQ table.  Each
**          table has 256 entries, so each VQ index is 8
**          bits.  (Only the LSP vector for subframe 3 is
**          quantized per frame.)
**
** Links to text:   Sections 2.6, 3.2
**
** Arguments:
**
**  FLOAT  *Lsp     Empty buffer
**  FLOAT  PrevLsp[]    Quantized LSP frequencies from the previous frame
**               (10 words)
**  Word32 LspId        Long word packed with the 3 VQ indices.  Band 0
**               corresponds to bits [23:16], band 1 corresponds
**               to bits [15:8], and band 2 corresponds to bits
**               [7:0].
**  Word16 Crc      Frame erasure indicator
**
** Outputs:
**
**  FLOAT  Lsp[]        Quantized LSP frequencies for current frame (10
**               words)
**
** Return value:         None
**
*/
void  Lsp_Inq(FLOAT *Lsp, FLOAT *PrevLsp, Word32 LspId, Word16 Crc)
{
    int    i,j;

    FLOAT *LspQntPnt;
    FLOAT  Lprd,Scon,Tmpf;
    int    Tmp;
    Flag   Test;

    /*
     * Check for frame erasure.  If a frame erasure has occurred, the
     * resulting VQ table entries are zero.  In addition, a different
     * fixed predictor and minimum frequency separation are used.
     */
    if (Crc == 0)
    {
        Scon = (FLOAT)2.0;
        Lprd = LspPred0;
    }
    else
    {
        LspId = (Word32) 0;
        Scon = (FLOAT)4.0;
        Lprd = LspPred1;
    }

    /*
     * Inverse quantize the 10th-order LSP vector.  Each band is done
     * separately.
     */

    for (i=LspQntBands-1; i >= 0; i--)
    {
        /* Get the VQ table entry corresponding to the transmitted index */
        Tmp = (int)(LspId & (Word32) 0x000000ff);
        LspId >>= 8;

        LspQntPnt = BandQntTable[i];

        for (j=0; j < BandInfoTable[i][1]; j++)
            Lsp[BandInfoTable[i][0] + j] = LspQntPnt[Tmp*BandInfoTable[i][1] + j];
    }

    /* Add predicted vector and DC to decoded vector */

    for (j=0; j < LpcOrder; j++)
        Lsp[j] = Lsp[j] + (PrevLsp[j] - LspDcTable[j])*Lprd + LspDcTable[j];


    /*
     * Perform a stability test on the quantized LSP frequencies.  This
     * test checks that the frequencies are ordered, with a minimum
     * separation between each.  If the test fails, the frequencies are
     * iteratively modified until the test passes.  If after 10
     * iterations the test has not passed, the previous frame's
     * quantized LSP vector is used.
     */

    for (i=0; i < LpcOrder; i++)
    {

        /* Check the first frequency */
        if (Lsp[0] < (FLOAT)3.0)
            Lsp[0] = (FLOAT)3.0;

        /* Check the last frequency */
        if (Lsp[LpcOrder-1] > (FLOAT)252.0)
            Lsp[LpcOrder-1] = (FLOAT)252.0;

        /* Perform the modification */
        for (j=1; j < LpcOrder; j++)
        {
            Tmpf = Scon + Lsp[j-1] - Lsp[j];
            if (Tmpf > 0)
            {
                Tmpf *= (FLOAT)0.5;
                Lsp[j-1] -= Tmpf;
                Lsp[j] += Tmpf;
            }
        }

        /* Test the modified frequencies for stability.  Break out of
         * the loop if the frequencies are stable.
         */

        Test = False;
        for (j=1; j < LpcOrder; j++)
            if ((Lsp[j] - Lsp[j-1]) < (Scon - (FLOAT)0.03125))
                Test = True;

        if (Test == False)
            break;
    }

    /*
     * If the result of the stability check is True (not stable),
     * set Lsp to PrevLsp
     */

    if (Test == True)
    {
        for ( j = 0 ; j < LpcOrder ; j ++ )
            Lsp[j] = PrevLsp[j] ;
    }

    return;
}


/*
**
** Function:            Lsp_Int()
**
** Description:     Computes the quantized LPC coefficients for a
**          frame.  First the quantized LSP frequencies
**          for all subframes are computed by linear
**          interpolation.  These frequencies are then
**          transformed to quantized LPC coefficients.
**
** Links to text:   Sections 2.7, 3.3
**
** Arguments:
**
**  FLOAT  *QntLpc      Empty buffer
**  FLOAT  CurrLsp[]    Quantized LSP frequencies for the current frame,
**               subframe 3 (10 words)
**  FLOAT  PrevLsp[]    Quantized LSP frequencies for the previous frame,
**               subframe 3 (10 words)
**
** Outputs:
**
**  FLOAT  QntLpc[]     Quantized LPC coefficients for current frame, all
**               subframes (40 words)
**  FLOAT  PrevLsp[]    Quantized LSP frequencies for the current frame,
**               subframe 3.  For use in the next frame. (10 words)
**
** Return value:        None
**
*/
void  Lsp_Int(FLOAT *QntLpc, FLOAT *CurrLsp, FLOAT *PrevLsp)
{
    int    i,j;

    FLOAT  *Dpnt;
    FLOAT  Fac[4] = {(FLOAT)0.25, (FLOAT)0.5, (FLOAT)0.75, (FLOAT)1.0};

    Dpnt = QntLpc;
    for (i=0; i < SubFrames; i++) {

        /* Compute the quantized LSP frequencies by linear interpolation
         * of the frequencies from subframe 3 of the current and
         * previous frames
         */

        for (j=0; j < LpcOrder; j++)
            Dpnt[j] = ((FLOAT)1.0 - Fac[i])*PrevLsp[j] + Fac[i]*CurrLsp[j];

        /* Convert the quantized LSP frequencies to quantized LPC
         * coefficients
         */

        LsptoA(Dpnt);
        Dpnt += LpcOrder;
    }
}


/*
**
** Function:            LsptoA()
**
** Description:     Converts LSP frequencies to LPC coefficients
**          for a subframe.  Sum and difference
**          polynomials are computed from the LSP
**          frequencies (which are the roots of these
**          polynomials).  The LPC coefficients are then
**          computed by adding the sum and difference
**          polynomials.
**
** Links to text:   Sections 2.7, 3.3
**
** Arguments:
**
**  FLOAT  Lsp[]        LSP frequencies (10 words)
**
** Outputs:
**
**  FLOAT  Lsp[]        LPC coefficients (10 words)
**
** Return value:        None
**
*/
void  LsptoA(FLOAT *Lsp)
{
    int   i,j;

    FLOAT P[LpcOrder/2+1];
    FLOAT Q[LpcOrder/2+1];
    FLOAT Floor;
    FLOAT Fac[(LpcOrder/2)-2] = {(FLOAT)1.0,(FLOAT)0.5,(FLOAT)0.25};

    /*
     * Compute the cosines of the LSP frequencies by table lookup and
     * linear interpolation
     */

    for (i=0; i < LpcOrder; i++)
    {
        Floor = (FLOAT)floor(Lsp[i]);
        j = (int) Floor;
        Lsp[i] = -(CosineTable[j] +
        (CosineTable[j+1]-CosineTable[j])*(Lsp[i]-Floor));
    }

    /*
     * Compute the sum and difference polynomials with the real roots
     * removed.  These are computed by polynomial multiplication as
     * follows.  Let the sum polynomial be P(z).  Define the elementary
     * polynomials P_i(z) = 1 - 2cos(w_i) z^{-1} + z^{-2}, for 1<=i<=
     * 5, where {w_i} are the LSP frequencies corresponding to the sum
     * polynomial.  Then P(z) = P_1(z)P_2(z)...P_5(z).  Similarly
     * the difference polynomial Q(z) = Q_1(z)Q_2(z)...Q_5(z).
     */

    /* Init P and Q. */

    P[0] = (FLOAT)0.5;
    P[1] = Lsp[0] + Lsp[2];
    P[2] = (FLOAT)1.0 + ((FLOAT)2.0)*Lsp[0]*Lsp[2];

    Q[0] = (FLOAT)0.5;
    Q[1] = Lsp[1] + Lsp[3];
    Q[2] = (FLOAT)1.0 + ((FLOAT)2.0)*Lsp[1]*Lsp[3];

    /* Compute the intermediate polynomials P_1(z)P_2(z)...P_i(z) and
     * Q_1(z)Q_2(z)...Q_i(z), for i = 2, 3, 4.  Each intermediate
     * polynomial is symmetric, so only the coefficients up to i+1 need
     * by computed.  Scale by 1/2 each iteration for a total of 1/8.
     */

    for (i=2; i < LpcOrder/2; i++)
    {
        /* Compute coefficient (i+1) */

        P[i+1] = P[i-1] + P[i]*Lsp[2*i+0];
        Q[i+1] = Q[i-1] + Q[i]*Lsp[2*i+1];

        /* Compute coefficients i, i-1, ..., 2 */

        for (j=i; j >= 2; j--)
        {
            P[j] = P[j-1]*Lsp[2*i+0] + ((FLOAT)0.5)*(P[j]+P[j-2]);
            Q[j] = Q[j-1]*Lsp[2*i+1] + ((FLOAT)0.5)*(Q[j]+Q[j-2]);
        }

        /* Compute coefficients 1, 0 */

        P[0] = P[0]*((FLOAT)0.5);
        Q[0] = Q[0]*((FLOAT)0.5);

        P[1] = (P[1] + Lsp[2*i+0]*Fac[i-2])*((FLOAT)0.5);
        Q[1] = (Q[1] + Lsp[2*i+1]*Fac[i-2])*((FLOAT)0.5);
    }

    /*
     * Convert the sum and difference polynomials to LPC coefficients
     * The LPC polynomial is the sum of the sum and difference
     * polynomials with the real zeros factored in: A(z) = 1/2 {P(z) (1
     * + z^{-1}) + Q(z) (1 - z^{-1})}.  The LPC coefficients are scaled
     * here by 16; the overall scale factor for the LPC coefficients
     * returned by this function is therefore 1/4.
     */

    for (i=0; i < LpcOrder/2; i++)
    {
        Lsp[i] =            (-P[i] - P[i+1] + Q[i] - Q[i+1])*((FLOAT)8.0);
        Lsp[LpcOrder-1-i] = (-P[i] - P[i+1] - Q[i] + Q[i+1])*((FLOAT)8.0);
    }
}