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Working around misdetected audio bandwidth

The new detector for SWB vs FB is unreliable due to the hack
that was required to get 24 kHz analysis working. We're now err
on the side of FB just to make sure.

--- a/src/analysis.c

+++ b/src/analysis.c

@@ -663,8 +663,10 @@

     }

     /* Special case for the last two bands, for which we don't have spectrum but only

        the energy above 12 kHz. */

-    {

+    if (tonal->Fs == 48000) {

+       float ratio;

        float E = hp_ener*(1.f/(240*240));

+       ratio = tonal->prev_bandwidth==20 ? 0.03f : 0.07f;

 #ifdef FIXED_POINT

        /* silk_resampler_down2_hp() shifted right by an extra 8 bits. */

        E *= 256.f*(1.f/Q15ONE)*(1.f/Q15ONE);

@@ -674,8 +676,11 @@

        E = MAX32(E, tonal->meanE[b]);

        /* Use a simple follower with 13 dB/Bark slope for spreading function */

        bandwidth_mask = MAX32(.05f*bandwidth_mask, E);

-       if (E>.1*bandwidth_mask && E*1e9f > maxE && E > noise_floor*160)

+       if (E>ratio*bandwidth_mask && E*1e9f > maxE && E > noise_floor*160)

           bandwidth = 20;

+       /* This detector is unreliable, so if the bandwidth is close to SWB, assume it's FB. */

+       if (bandwidth >= 17)

+          bandwidth = 20;

     }

     if (tonal->count<=2)

        bandwidth = 20;

@@ -896,6 +901,7 @@

 #endif

     info->bandwidth = bandwidth;

+    tonal->prev_bandwidth = bandwidth;

     /*printf("%d %d\n", info->bandwidth, info->opus_bandwidth);*/

     info->noisiness = frame_noisiness;

     info->valid = 1;

--- a/src/analysis.h

+++ b/src/analysis.h

@@ -55,6 +55,7 @@

    int   mem_fill;                      /* number of usable samples in the buffer */

    float prev_band_tonality[NB_TBANDS];

    float prev_tonality;

+   int prev_bandwidth;

    float E[NB_FRAMES][NB_TBANDS];

    float logE[NB_FRAMES][NB_TBANDS];

    float lowE[NB_TBANDS];