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Encoders: Add a little dithering with the fractional bit for mono mixdowns so faster shifts can be used again instead of division without introducing their own DC offset into the mixed channels.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@12246 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Michael Sevakis 2007-02-09 18:11:11 +00:00
parent 0abfe9f8ea
commit d52f2e4bca
4 changed files with 34 additions and 12 deletions
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7
apps/codecs/mp3_enc.c
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@ -174,6 +174,7 @@ static unsigned samp_per_frame IBSS_ATTR;
static config_t cfg IBSS_ATTR;
static char *res_buffer;
static int32_t err IBSS_ATTR;
static const uint8_t ht_count_const[2][2][16] =
{ { { 1, 5, 4, 5, 6, 5, 4, 4, 7, 3, 6, 0, 7, 2, 3, 1 }, /* table0 */
@ -2055,7 +2056,9 @@ static void to_mono_mm(void)
inline void to_mono(uint32_t **samp)
{
int32_t lr = **samp;
int32_t m = ((int16_t)lr + (lr >> 16)) / 2;
int32_t m = (int16_t)lr + (lr >> 16) + err;
err = m & 1;
m >>= 1;
*(*samp)++ = (m << 16) | (uint16_t)m;
} /* to_mono */
@ -2434,6 +2437,8 @@ static bool enc_init(void)
init_mp3_encoder_engine(inputs.sample_rate, inputs.num_channels,
inputs.config);
err = 0;
/* configure the buffer system */
params.afmt = AFMT_MPA_L3;
params.chunk_size = cfg.byte_per_frame + 1;