softvol can be also a pass-thru when the given control already exists
as a hardware control, and the name isn't set properly because of
slave creation. This patch fixes it.
This patch allows for gain in the softvol plugin, in addition to attenuation.
The plugin now has a "max_dB" parameter (up to 50 dB) as well as the
original "min_dB" parameter (down to -51 dB). max_dB defaults to 0 dB, so
unless max_dB is specified in a device conf, the behavior of the plugin will
be the same as before (attenuation only).
HDA-Intel.conf is also modified to use softvol for its default capture.
So now, capture is filtered through softvol (range -30 to +30 dB) before
being passed on to dsnoop as before.
The softvol plugin allows a range of -51 to +50 dB, so max_dB could be
increased to 50. But eventually samples are going to get clipped. At 40
dB I was beginning to get clipping when recording a sample sound at a
"reasonably soft" volume using a digital mic on the stac9205 HDA codec.
The motivation for this work is that some HDA codecs have no hardware gain
control for some paths. For instance, the stac9205 has support for digital
mics, but there is no gain control widget for this signal before it is placed
on the Azalia link (only a mute). Therefore gain can only be accomplished
via software.
Signed-off-by: Steve Longerbeam <stevel@embeddedalley.com>
Here's a patch which adds support for S24_3LE and byte-swapped S16 and
S32 to softvol. I've tested S24_3LE and byte-swapped S16 on powerpc
with snd-usb-audio. All other cases are untested so far.
(Config at http://blog.blackdown.de/static/alsa/USB-Audio.conf)
Signed-off-by: Juergen Kreileder <jk@blackdown.de>
Fixed the bug producing silent tones with some combinations of plugins.
The internal buffer handling is now better (cleaner) integrated with
snd_pcm_generic_*().
- added link/unlink/link_fd fast_ops callbacks
- moved code from snd_pcm_link to pcm_hw.c
- moved "empty" routines pointing to slave to pcm_generic.c
- introduced snd_pcm_generic_t
The softvol PCM plugin is added. It applies the software volume attenuation,
which may be useful for codecs without volume controls.
Currently, the control is only mono. The attenuation is applied to all
channels equally. The control is probed and automatically created
when not exists yet.
