Greatly reduce volume-change zipper artifacts with SW volume.

Uses a cosine factor to smoothly shift the PCM level from the old level
to the new one over the length of a frame.

Implements indirect calls to PCM scaling function instead of testing
conditions on every callback, cleanly assigning a different call to
do the volume transition. The volume change call then assigns the final
scaling function.

Change-Id: If1004b92a91c5ca766dd0e4014ec274636e8ed26
Reviewed-on: http://gerrit.rockbox.org/763
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested: Michael Sevakis <jethead71@rockbox.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/firmware/export/pcm-internal.h b/firmware/export/pcm-internal.h
index 2b73f64ef6..7670f99f04 100644
--- a/firmware/export/pcm-internal.h
+++ b/firmware/export/pcm-internal.h
@@ -57,6 +57,7 @@ void pcm_sw_volume_copy_buffer(void *dst, const void *src, size_t size);
 #endif
 #endif /* PCM_SW_VOLUME_UNBUFFERED */
 
+void pcm_sync_pcm_factors(void);
 #endif /* HAVE_SW_VOLUME_CONTROL */
 
 #define PCM_SAMPLE_SIZE     (2 * sizeof (int16_t))