From 0078837a9760b8b5a14c87af0cb44a107462db7b Mon Sep 17 00:00:00 2001 From: Max Kellermann Date: Thu, 23 Oct 2008 16:58:07 +0200 Subject: pcm_dither: added generic 24 to 16 bit dithering Copied and adapted code from the mp3 decoder plugin. This library now replaces the old and low-quality function pcm_convert_24_to_16(). --- src/Makefile.am | 2 ++ src/pcm_dither.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ src/pcm_dither.h | 41 ++++++++++++++++++++++++++++ src/pcm_utils.c | 18 +++++++------ src/pcm_utils.h | 4 +++ 5 files changed, 139 insertions(+), 8 deletions(-) create mode 100644 src/pcm_dither.c create mode 100644 src/pcm_dither.h (limited to 'src') diff --git a/src/Makefile.am b/src/Makefile.am index 17234ca30..f2bf55eb1 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -66,6 +66,7 @@ mpd_headers = \ path.h \ mapper.h \ pcm_utils.h \ + pcm_dither.h \ permission.h \ player_thread.h \ player_control.h \ @@ -145,6 +146,7 @@ mpd_SOURCES = \ path.c \ mapper.c \ pcm_utils.c \ + pcm_dither.c \ permission.c \ player_thread.c \ player_control.c \ diff --git a/src/pcm_dither.c b/src/pcm_dither.c new file mode 100644 index 000000000..1296d0926 --- /dev/null +++ b/src/pcm_dither.c @@ -0,0 +1,82 @@ +/* the Music Player Daemon (MPD) + * Copyright (C) 2008 Max Kellermann + * This project's homepage is: http://www.musicpd.org + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include "pcm_dither.h" + +static unsigned long prng(unsigned long state) +{ + return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL; +} + +static int16_t +pcm_dither_sample_24_to_16(int32_t sample, struct pcm_dither_24 *dither) +{ + int32_t output, rnd; + + enum { + from_bits = 24, + to_bits = 16, + scale_bits = from_bits - to_bits, + round = 1 << (scale_bits - 1), + mask = (1 << scale_bits) - 1, + ONE = 1 << (from_bits - 1), + MIN = -ONE, + MAX = ONE - 1 + }; + + sample += dither->error[0] - dither->error[1] + dither->error[2]; + + dither->error[2] = dither->error[1]; + dither->error[1] = dither->error[0] / 2; + + /* round */ + output = sample + round; + + rnd = prng(dither->random); + output += (rnd & mask) - (dither->random & mask); + + dither->random = rnd; + + /* clip */ + if (output > MAX) { + output = MAX; + + if (sample > MAX) + sample = MAX; + } else if (output < MIN) { + output = MIN; + + if (sample < MIN) + sample = MIN; + } + + output &= ~mask; + + dither->error[0] = sample - output; + + return (int16_t)(output >> scale_bits); +} + +void +pcm_dither_24_to_16(struct pcm_dither_24 *dither, + int16_t *dest, const int32_t *src, + unsigned num_samples) +{ + while (num_samples-- > 0) + *dest++ = pcm_dither_sample_24_to_16(*src++, dither); +} diff --git a/src/pcm_dither.h b/src/pcm_dither.h new file mode 100644 index 000000000..202521497 --- /dev/null +++ b/src/pcm_dither.h @@ -0,0 +1,41 @@ +/* the Music Player Daemon (MPD) + * Copyright (C) 2008 Max Kellermann + * This project's homepage is: http://www.musicpd.org + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#ifndef PCM_DITHER_H +#define PCM_DITHER_H + +#include + +struct pcm_dither_24 { + int32_t error[3]; + int32_t random; +}; + +static inline void +pcm_dither_24_init(struct pcm_dither_24 *dither) +{ + dither->error[0] = dither->error[1] = dither->error[2] = 0; + dither->random = 0; +} + +void +pcm_dither_24_to_16(struct pcm_dither_24 *dither, + int16_t *dest, const int32_t *src, + unsigned num_samples); + +#endif diff --git a/src/pcm_utils.c b/src/pcm_utils.c index bd7fc0482..8d5bed990 100644 --- a/src/pcm_utils.c +++ b/src/pcm_utils.c @@ -208,6 +208,8 @@ void pcm_mix(char *buffer1, const char *buffer2, size_t size, void pcm_convert_init(struct pcm_convert_state *state) { memset(state, 0, sizeof(*state)); + + pcm_dither_24_init(&state->dither); } #ifdef HAVE_LIBSAMPLERATE @@ -457,17 +459,16 @@ pcm_convert_8_to_16(int16_t *out, const int8_t *in, } static void -pcm_convert_24_to_16(int16_t *out, const int32_t *in, +pcm_convert_24_to_16(struct pcm_dither_24 *dither, + int16_t *out, const int32_t *in, unsigned num_samples) { - while (num_samples > 0) { - *out++ = *in++ >> 8; - --num_samples; - } + pcm_dither_24_to_16(dither, out, in, num_samples); } static const int16_t * -pcm_convert_to_16(uint8_t bits, const void *src, +pcm_convert_to_16(struct pcm_convert_state *convert, + uint8_t bits, const void *src, size_t src_size, size_t *dest_size_r) { static int16_t *buf; @@ -500,7 +501,8 @@ pcm_convert_to_16(uint8_t bits, const void *src, buf = xrealloc(buf, len); } - pcm_convert_24_to_16((int16_t *)buf, + pcm_convert_24_to_16(&convert->dither, + (int16_t *)buf, (const int32_t *)src, num_samples); return buf; @@ -524,7 +526,7 @@ size_t pcm_convert(const struct audio_format *inFormat, assert(outFormat->bits == 16); /* everything else supports 16 bit only, so convert to that first */ - buf = pcm_convert_to_16(inFormat->bits, src, src_size, &len); + buf = pcm_convert_to_16(convState, inFormat->bits, src, src_size, &len); if (!buf) exit(EXIT_FAILURE); diff --git a/src/pcm_utils.h b/src/pcm_utils.h index 3fc15e8b7..835ba187f 100644 --- a/src/pcm_utils.h +++ b/src/pcm_utils.h @@ -20,6 +20,7 @@ #define PCM_UTILS_H #include "../config.h" +#include "pcm_dither.h" #include #include @@ -40,6 +41,9 @@ struct pcm_convert_state { uint32_t lastInSampleRate; uint32_t lastOutSampleRate; #endif + + struct pcm_dither_24 dither; + /* Strict C99 doesn't allow empty structs */ int error; }; -- cgit v1.2.3