[FFmpeg-devel] [PATCH] Common ACELP code & G.729 [6/7] - G.729 postfilter

[Michael Niedermayer]

On Fri, May 02, 2008 at 06:49:43PM +0700, Vladimir Voroshilov wrote:
> Patch contains G.729 postfilter.
> It was separated due to large size to help reviewing.
> G.729 can produce audible speech even without this postfilter.
> 
> -- 
> Regards,
> Vladimir Voroshilov mailto:voroshil at gmail.com
> JID: voroshil at gmail.com, voroshil at jabber.ru
> ICQ: 95587719

> diff --git a/libavcodec/g729postfilter.c b/libavcodec/g729postfilter.c
> new file mode 100644
> index 0000000..b09d463
> --- /dev/null
> +++ b/libavcodec/g729postfilter.c
> @@ -0,0 +1,704 @@
> +#include <inttypes.h>
> +#include <limits.h>
> +
> +#include "avcodec.h"
> +#include "g729.h"
> +#include "acelp_pitch_lag.h"
> +#include "g729postfilter.h"
> +#include "acelp_math.h"
> +#include "acelp_filters.h"
> +
> +#define FRAC_BITS 15
> +#include "mathops.h"
> +

> +/**
> + * formant_pp_factor_num_pow[i] = FORMANT_PP_FACTOR_NUM^i
> + */
> +static const int16_t formant_pp_factor_num_pow[11]=
> +{
> +  /* (0.15) */
> +  32768, 18022, 9912, 5451, 2998, 1649, 907, 499, 274, 151, 83
     ^^^^^
doesnt fit in int16_t, it does fir in uint16_t though


[...]
> +static void g729_residual(int16_t* filter_coeffs, const int16_t* speech, int16_t* residual, int subframe_size, int16_t* res_filter_data)
> +{
> +    int i, n, sum;
> +
> +    /*
> +      4.2.1, Equation 79 Residual signal calculation
> +      ( filtering through A(z/FORMANT_PP_FACTOR_NUM) , one half of short-term filter)
> +    */

> +    for(n=0; n<subframe_size; n++)
> +    {
> +        sum = res_filter_data[10+n] = speech[n];

this is effectively a memcpy() and i do not like memcpy() ...


> +
> +        sum <<= 12;
> +        for(i=0; i<10; i++)
> +            sum += filter_coeffs[i] * res_filter_data[10+n-i-1];
> +
> +        residual[n] = (sum + 0x800) >> 12;

sum= x<<12
sum += blah
y= (sum+z) >> 12;

can be changed to

sum= z
sum += blah
y= (sum >> 12) + x;

which does 1 shift less



[...]
> +    if (shift>0)
> +        for(i=0; i<subframe_size + RES_PREV_DATA_SIZE; i++)
> +	    sig_scaled[i] = residual[i] >> shift;

tabs


[...]
> +        /*
> +          Recompute delayed signal with an interpolation filter of length 129
> +        */
> +        for(n=0; n<subframe_size; n++)
> +        {
> +            sum = 0;
> +            for(i=0;i<LONG_INT_FILT_LEN; i++)
> +                sum += ff_g729_interp_filt_long[best_delay_frac-1][i] *
> +                       sig_scaled[n - (best_delay_int + 1 - delayed_signal_offset) + (LONG_INT_FILT_LEN/2 - i) + RES_PREV_DATA_SIZE];
> +            residual_filt[n] = (sum + 0x4000) >> 15;
> +        }

duplicate, there already was some interpolation code somewhere else in g729


[...]
> +static int16_t g729_get_tilt_comp(int16_t *lp_gn, const int16_t *lp_gd, int16_t* speech, int subframe_size)
> +{
> +    int rh1,rh0; // Q12
> +    int sum, temp;
> +    int i, n;
> +    int gain_term; //gain term for short-term postfilter
> +
> +    lp_gn[10] = 4096; //1.0 in Q12
> +
> +    /* Apply 1/A(z/FORMANT_PP_FACTOR_DEN) filter to hf */

> +    for(n=0; n<22; n++)
> +    {
> +        sum = lp_gn[n+11] << 12;
> +        for(i=0; i<10; i++)
> +            sum -= lp_gd[i+1] * lp_gn[n+11-i-1];
> +        sum = av_clip(sum, -0x08000000, 0x07ffffff);
> +
> +        lp_gn[n+11] = (sum + 0x800) >> 12;
> +    }

This filter looks duplicated as well


> +    /* Now lp_gn (starting with 10) contains impulse response of A(z/FORMANT_PP_FACTOR_NUM)/A(z/FORMANT_PP_FACTOR_DEN) filter */
> +

> +    /* 4.2.3, Equation 87, calcuate rh(0)  */
> +    rh0 = sum_of_squares(lp_gn + 10, 20, 0, 0) << 1;   // Q24 -> Q9

> +    temp = 30 - av_log2(rh0);
> +    if(temp > 16)
> +        rh0 <<= temp - 16;
> +    else
> +        rh0 >>= 16 - temp;
> +
[...]
> +    if(temp > 16)
> +        rh1 <<= temp - 16;
> +    else
> +        rh1 >>= 16 - temp;

looks useless, this just reduces precission


[...]
> +            if(exp_after - exp_before - 1 > 0)
> +                gain <<= exp_after - exp_before - 1;
> +            else
> +                gain >>= exp_before - exp_after + 1;

This stuff is duplicated all over the place and should be in a fuction

Anyway the whole postfilter looks like it needs some serious cleanup.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
it to them? Then do not be too eager to deal out death in judgement. For
even the very wise cannot see all ends. -- Gandalf
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