[FFmpeg-devel] [PATCH] Common ACELP routines (2/3) - filters

[Vladimir Voroshilov]

On Sun, Apr 27, 2008 at 10:57 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>
> On Sun, Apr 27, 2008 at 08:39:15PM +0700, Vladimir Voroshilov wrote:

[...]

>  > Here is latest version.
>
> [...]
>  > +void ff_acelp_interpolate_excitation(
>  > +        int16_t* ac_v,
>  > +        int pitch_delay_int,
>  > +        int pitch_delay_frac,
>
> > +        int subframe_size)
>  > +{
>  > +    int n, i;
>  > +    int v;
>  > +
>  > +    /* The lookup table contain values corresponding
>  > +       to -2/6 -1/6 0 1/6 2/6 3/6 fraction order.
>
> > +       The filtering process uses a negative pitch lag offset, but
>  > +       a negative offset should not be used in then table. To avoid
>  > +       a negative offset in the table dimension corresponding to
>  > +       fractional delay the following conversion applies:
>  > +
>
>  trailing whitespace

Fixed.

>  > +       -pitch_delay = -(6*pitch_delay_int+pitch_delay_frac) =
>  > +
>  > +       =  -6*pitch_delay_int - pitch_delay_frac =
>  > +
>  > +         / -6*(pitch_delay_int)   - pitch_delay_frac,     pitch_delay_frac <  0
>  > +       =<
>  > +         \ -6*(pitch_delay_int+1) + (6-pitch_delay_frac), pitch_delay_frac >= 0
>  > +    */
>  > +
>  > +    /* Compute negative value of fractional delay */
>  > +    pitch_delay_frac = - pitch_delay_frac;
>  > +
>
>  > +    /* Now make sure that pitch_delay_frac will always be positive */
>
> > +    if(pitch_delay_frac < 0)
>  > +    {
>  > +        pitch_delay_frac += 6;
>  > +        pitch_delay_int++;
>  > +    }
>
>  Can it really be >= 0 and <0 ?

Didn't understand you.
According to current pitch delay decode routine pitch_delay_frac
belongs to [-2; 3]
-pitch_delay_frac belongs to [-3; 2]

>  > +void ff_acelp_weighted_filter(
>  > +        int16_t *out,
>  > +        const int16_t* in,
>  > +        int16_t weight,
>  > +        int filter_length)
>  > +{
>  > +    int weight_pow = 1 << 15;
>  > +    int n;
>  > +
>  > +    for(n=0; n<filter_length; n++)
>  > +    {
>  > +        /* (0.15) * (3.12) and (3.27) -> (3.12) with rounding */
>  > +        out[n] = (in[n] * weight_pow + 0x4000) >> 15;
>  > +        /* (0.15) * (3.12) and (3.27) -> (3.12) with rounding */
>  > +        weight_pow = (weight_pow * weight + 0x4000) >> 15;
>  > +    }
>  > +}
>
>  as weight is a constant weight_pow is as well and half of the computations
>  are unneeded

Now routine accepts array of constants.

>  > +void ff_acelp_high_pass_filter(
>  > +        int16_t* out,
>
> > +        int16_t* hpf_z,
>  > +        int* hpf_f,
>  > +        const int16_t* in,
>
> > +        int length)
>  > +{
>  > +    int i;
>  > +
>  > +    for(i=0; i<length; i++)
>  > +    {
>  > +        memmove(hpf_z + 1, hpf_z, 2 * sizeof(hpf_z[0]));
>  > +        hpf_z[0] = in[i];
>
> > +
>  > +        hpf_f[0] =  MULL(hpf_f[1], 15836);
>  > +        hpf_f[0] += MULL(hpf_f[2], -7667);
>  > +
>  > +        hpf_f[0] += 7699 * (hpf_z[0] - 2*hpf_z[1] + hpf_z[2]);
>  > +
>  > +        /* Clippin is required to pass G.729 OVERFLOW test */
>
> > +        if(hpf_f[0] >= 0xfffffff)
>  > +        {
>  > +            out[i] = SHRT_MAX;
>
> > +            hpf_f[0] = 0x3fffffff;
>  > +        }
>  > +        else if (hpf_f[0] <= -0x10000000)
>  > +        {
>  > +            out[i] = SHRT_MIN;
>
> > +            hpf_f[0] = -0x40000000;
>  > +        }
>  > +        else
>  > +        {
>
>  > +            hpf_f[0] <<= 2;
>
>  The shift is avoidable i think as already said

Changed and added comment about bitexactness.

There is also some not clear thing for me..
ff_acelp_interpolate_excitation (according to math) is just  an low-pass filter.
But it is intended to build adaptive-codebook (pitch) vector from
previous speech data.
I wonder should it be moved to something like acelp_vectors.c (along
with fixed codebook (innovation) vector decoding, fixed vector
updating and building excitation signal from pitch and innovation
vectors) ?

-- 
Regards,
Vladimir Voroshilov mailto:voroshil at gmail.com
JID: voroshil at gmail.com, voroshil at jabber.ru
ICQ: 95587719
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