Correction of musepack SV8 replaygain. The album/title peak is saved in a logarithmic representation and needs to be converted to linear fixed point for further processing.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@25187 a1c6a512-1295-4272-9138-f99709370657
diff --git a/apps/metadata/mpc.c b/apps/metadata/mpc.c
index a8cd128..c6f3c3d 100644
--- a/apps/metadata/mpc.c
+++ b/apps/metadata/mpc.c
@@ -8,6 +8,7 @@
* $Id$
*
* Copyright (C) 2005 Thom Johansen
+ * Copyright (C) 2010 Andree Buschmann
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
@@ -27,9 +28,11 @@
#include "metadata_parsers.h"
#include "logf.h"
#include "replaygain.h"
+#include "fixedpoint.h"
-/* Needed for replay gain in sv8, please search MPC_OLD_GAIN_REF in libmusepack */
-#define SV8_TO_SV7_CONVERT_GAIN (6482) /* 64.82 * 100 */
+/* Needed for replay gain and clipping prevention of SV8 files. */
+#define SV8_TO_SV7_CONVERT_GAIN (6482) /* 64.82 * 100, MPC_OLD_GAIN_REF */
+#define SV8_TO_SV7_CONVERT_PEAK (23119) /* 256 * 20 * log10(32768) */
static int set_replaygain_sv7(struct mp3entry* id3,
bool album,
@@ -39,15 +42,9 @@
long gain = (int16_t) ((value >> 16) & 0xffff);
long peak = (uint16_t) (value & 0xffff);
- /* Remark: mpc sv7 outputs peak as amplitude, not as dB. The following
- * useage of peak is not correct and needs to be fixed. */
-
/* We use a peak value of 0 to indicate a given gain type isn't used. */
if (peak != 0) {
- /* Use the Xing TOC field to store ReplayGain strings for use in the
- * ID3 screen, since Musepack files shouldn't need to use it in any
- * other way.
- */
+ /* Save the ReplayGain data to id3-structure for further processing. */
used += parse_replaygain_int(album, gain * 512 / 100, peak << 9,
id3, id3->toc + used, sizeof(id3->toc) - used);
}
@@ -63,13 +60,19 @@
{
gain = (long)(SV8_TO_SV7_CONVERT_GAIN - ((gain*100)/256));
+ /* Transform SV8's logarithmic peak representation to the desired linear
+ * representation: linear = pow(10, peak/256/20).
+ *
+ * FP_BITS = 24 bits = desired fp representation for dsp routines
+ * FRAC_BITS = 12 bits = resolution used for fp_bits
+ * fp_factor(peak*(1<<FRAC_BITS)/256, FRAC_BITS) << (FP_BITS-FRAC_BITS)
+ **/
+ peak = (fp_factor((peak-SV8_TO_SV7_CONVERT_PEAK)*16, 12) << 12);
+
/* We use a peak value of 0 to indicate a given gain type isn't used. */
if (peak != 0) {
- /* Use the Xing TOC field to store ReplayGain strings for use in the
- * ID3 screen, since Musepack files shouldn't need to use it in any
- * other way.
- */
- used += parse_replaygain_int(album, gain * 512 / 100, peak << 9,
+ /* Save the ReplayGain data to id3-structure for further processing. */
+ used += parse_replaygain_int(album, gain * 512 / 100, peak,
id3, id3->toc + used, sizeof(id3->toc) - used);
}