[FFmpeg-devel] [PATCH] Move pitch vector interpolation filter to acelp_filters.

[Michael Niedermayer]

On Sun, May 18, 2008 at 12:23:32AM +0700, Vladimir Voroshilov wrote:
> Attached patch does $subj.
> 
> Filter was extended recently and now receives
> filter coefficients and filter length as parameters.
> 
> Since this makes the filter more common, Michael suggested to move it
> along with used filter tables from acelp_vectors to acelp_filter.
[...]
> +const int16_t ff_acelp_interp_filter[66] =
> +{ /* (0.15) */
> +  29443, 28346, 25207, 20449, 14701,  8693,
> +   3143, -1352, -4402, -5865, -5850, -4673,
> +  -2783,  -672,  1211,  2536,  3130,  2991,
> +   2259,  1170,     0, -1001, -1652, -1868,
> +  -1666, -1147,  -464,   218,   756,  1060,
> +   1099,   904,   550,   135,  -245,  -514,
> +   -634,  -602,  -451,  -231,     0,   191,
> +    308,   340,   296,   198,    78,   -36,
> +   -120,  -163,  -165,  -132,   -79,   -19,
> +     34,    73,    91,    89,    70,    38,
> +      0,     0,     0,     0,     0,     0,
> +};
> +
> +const int16_t ff_g729_interp_filt_short[(ANALYZED_FRAC_DELAYS+1)*(SHORT_INT_FILT_LEN+1)] =
> +{
> +      0, 31650, 28469, 23705, 18050, 12266,  7041,  2873,
> +      0, -1597, -2147, -1992, -1492,  -933,  -484,  -188,
> +      0,     0,     0,     0,     0,     0,     0,     0,
> +};
> +
> +const int16_t ff_g729_interp_filt_long[(ANALYZED_FRAC_DELAYS+1)*(LONG_INT_FILT_LEN+1)] =
> +{
> +   0, 31915, 29436, 25569, 20676, 15206,  9639,  4439,
> +   0, -3390, -5579, -6549, -6414, -5392, -3773, -1874,
> +   0,  1595,  2727,  3303,  3319,  2850,  2030,  1023,
> +   0,  -887, -1527, -1860, -1876, -1614, -1150,  -579,
> +   0,   501,   859,  1041,  1044,   892,   631,   315,
> +   0,  -266,  -453,  -543,  -538,  -455,  -317,  -156,
> +   0,   130,   218,   258,   253,   212,   147,    72,
> +   0,   -59,  -101,  -122,  -123,  -106,   -77,   -40,
> +   0,     0,     0,     0,     0,     0,     0,     0,
> +};

"ff_g729*" tables should be in g729 related files so they are
not included in the binary if g729 is disabled but some other ACELP codec
is compiled in


> +
> +void ff_acelp_interpolate_pitch_vector(
> +        int16_t* out,
> +        const int16_t* in,
> +        const int16_t* filter_coeffs,
> +        int precision,
> +        int pitch_delay_int,
> +        int pitch_delay_frac,
> +        int filter_length,
> +        int subframe_size)
> +{
> +    int n, i;
> +
> +    /* pitch_delay_frac [0; 5]
> +       pitch_delay_int  [PITCH_LAG_MIN; PITCH_LAG_MAX] */
> +    for(n=0; n<subframe_size; n++)
> +    {
> +        int idx = precision;
> +        /* 3.7.1 of G.729, Equation 40 */
> +        int v = in[n - pitch_delay_int] * filter_coeffs[FFABS(pitch_delay_frac)];
> +        for(i=1; i<filter_length+1; i++)
> +        {
> +
> +            /* The reference G.729 and AMR fixed point code performs clipping after
> +               each of the two following accumulations.
> +               Since clipping affects only the synthetic OVERFLOW test without
> +               causing an int type overflow, it was moved outside the loop. */
> +
> +            /*  R(x):=ac_v[-k+x]
> +                v += R(n-i)*ff_acelp_interp_filter(t+6i)
> +                v += R(n+i+1)*ff_acelp_interp_filter(6-t+6i) */
> +
> +            v += in[n - pitch_delay_int - i] * filter_coeffs[idx - pitch_delay_frac];
> +            v += in[n - pitch_delay_int + i] * filter_coeffs[idx + pitch_delay_frac];
> +            idx += precision;
> +        }
> +        out[n] = av_clip_int16((v + 0x4000) >> 15);
> +    }
> +}

This code is written for a filter with an odd number of coeffs (1,3,5,...) but
all but the first filter for which it is used have an even number thus they
end up needing these 0 coeffs.
The code should be changed so it expects even number of coeff filters and the
unneeded 0 elements should be removed from the tables

anyway, the obvious implementation is:

for(n=0; n<subframe_size; n++){
    int idx = precision>>1;
    int v = 0x4000;
    for(i=1; i<filter_length+1; i++){
        v += in[n - pitch_delay_int - i] * filter_coeffs[idx - frac];
        v += in[n - pitch_delay_int + i] * filter_coeffs[idx + frac];
        idx += precision;
    }
    out[n] = av_clip_int16(v >> 15);

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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