[mythtv-users] mythmusic alsa digital output setup

[Harry Coin]

Mythmusic users using digital outputs based on the Intel ICHx family 
have the challenge of playing back 44.1khz or other bitrate encoded 
files on chips that only do 48Khz digital output well.  Others have more 
robust digital outputs, but digital playback devices that only do DVD 
44.8Khz audio well.   Here's the answer.

Various ALSA configurations offered online attempt to patch this, I 
struggled with half right configuration file examples, iffy mixer 
permissions and all manner of jiggery-pokery on something that should 
have been easy.   Anyhow, 1.  make sure your user is in the OS audio group.

Set your mythmusic's output device to be

ALSA:plug:mixed-digital

Put this in /etc/asound.conf and make sure there isn't a contrading 
.asoundrc in the user's home directory. Note this is for the ICH5 chip 
installed as device 0 (typical), with the digital sub-device numbered 
'4' (sometimes it's 1, who knows).  If you have something else, use 
'aplay -l' to list what you have, you'll see 'card X:' and 'device Y' on 
a line with IEC958 or SPDIF or similar. then edit just the section 
titled pcm.digital-hw below.  Here's the /etc/asound.conf file
-----

# ~/.asoundrc or /etc/asound.conf
# ALSA configuration file

##### USAGE #####
# Save this file as "~/.asoundrc" (for user-specific sound configuration) or
# "/etc/asound.conf" (for system-wide sound configuration) and specify ALSA
# device names ad described in the next section.


##### DEVICE NAMES #####
# This configuration file defines four devices for use by the user.  Those
# devices are "analog", "mixed-analog", "digital", and "mixed-digital".  The
# user may also re-define "default" to be identical to one of the 
above-named
# devices (i.e. to send all sound output to the digital output unless 
otherwise
# specified).  Use the device names as described below:
#  - "analog" outputs to the analog output directly and (at least on 
software
#  sound cards) blocks other audio output.  After playback completes, 
"queued"
#  sounds are output in sequence.
#  - "mixed-analog" mixes audio output from multiple programs into the 
analog
#  output (so you can hear beeps, alerts, and other noises while playing 
back
#  an audio stream).
#  - "digital" outputs to the digital output directly.  Since most (all?)
#  digital outputs expect 48kHz PCM audio, this may not work for some 
playback
#  (i.e. CD's--which are 44.1kHz PCM audio--or 32kHz audio streams from TV
#  recordings, etc.).
#  - "mixed-digital"

# All other devices created within this file are used only by the 
configuration
# file itself and should /not/ be used directly.  In other words, do not use
# the devices "analog-hw", "dmix-analog", "digital-hw", or "dmix-digital".


##### IMPORTANT #####
# To make this ALSA configuration file work with your sound card, you 
will need
# to define the appropriate card and device information for the 
"analog-hw" and
# "digital-hw" devices below.  You can find the card and device information
# using "aplay -l".


##### Configuration File #####

# Override the default output used by ALSA.  If you do not override the
# default, your default device is identical to the (unmixed) "analog" device
# shown below.  If you prefer mixed and/or digital output, uncomment the
# appropriate four lines below (only one slave.pcm line).
#
# Note, also, that as of ALSA 1.0.9, "software" sound cards have been 
modified
# such that their default "default" device is identical to the 
"mixed-analog"
# device.  Whether using an ALSA version before or after 1.0.9, it does 
no harm
# and has no affect on performance to redefine the device (even if the
# redefinition does not change anything).  Also, by using this ALSA
# configuration file, you once again have access to unmixed analog 
output using
# the "analog" device.
pcm.!default {
   type plug
## Uncomment the following to use "mixed-analog" by default
#  slave.pcm "dmix-analog"
## Uncomment the following to use (unmixed) "digital" by default
#  slave.pcm "digital-hw"
## Uncomment the following to use "mixed-digital" by default
   slave.pcm "dmix-digital"
}

# Control device (mixer, etc.) for the card
ctl.!default {
   type hw
   card 0
}

# Alias for (converted) analog output on the card
# - This is identical to the device named "default"--which always exists and
# refers to hw:0,0 (unless overridden)
# - Therefore, we can specify "hw:0,0", "default", or "analog" to access 
analog
# output on the card
# - Note that as of ALSA 1.0.9, "software" sound card definitions redefine
# "default" to do mixing, meaning this device is different from 
"default" and
# allows playback while blocking other sound sources (until playback
# completes).
pcm.analog {
   type plug
   slave.pcm "analog-hw"
}

# Control device (mixer, etc.) for the card
ctl.analog {
   type hw
   card 0
}

# Alias for (converted) mixed analog output on the card
# - This will accept audio input--regardless of rate--and convert to the 
rate
# required for the dmix plugin (in this case 48000Hz)
# - Note that as of ALSA 1.0.9, "software" sound card definitions redefine
# "default" to do mixing, meaning this device is identical to "default" for
# "software" sound cards.
pcm.mixed-analog {
   type plug
   slave.pcm "dmix-analog"
}

# Control device (mixer, etc.) for the card
ctl.mixed-analog {
   type hw
   card 0
}

# Alias for (converted) digital (S/PDIF) output on the card
# - This will accept audio input--regardless of rate--and convert to the 
rate
# required for the S/PDIF hardware (in this case 48000Hz)
pcm.digital {
   type plug
   slave.pcm "digital-hw"
}

# Control device (mixer, etc.) for the card
ctl.digital {
   type hw
   card 0
}

# Alias for mixed (converted) digital (S/PDIF) output on the card
#  - This will accept audio input--regardless of rate--and convert to 
the rate
#  required for the S/PDIF hardware (in this case 48000Hz)
pcm.mixed-digital {
   type plug
   slave.pcm "dmix-digital"
}

# Control device (mixer, etc.) for the card
ctl.mixed-digital {
   type hw
   card 0
}

# The following devices are not useful by themselves.  They require specific
# rates, channels, and formats.  Therefore, you probably do not want to use
# them directly.  Instead use of of the devices defined above.

# Alias for analog output on the card
# Do not use this directly--it requires specific rate, channels, and format
pcm.analog-hw {
   type hw
   card 0
   # The default value for device is 0, so no need to specify
#  - Uncomment one of the below or create a new "device N" line as 
appropriate
#    for your sound card or
#  device 1
#  device 4
}

# Control device (mixer, etc.) for the card
ctl.analog-hw {
   type hw
   card 0
}

# Alias for digital (S/PDIF) output on the card
# Do not use this directly--it requires specific rate, channels, and format
pcm.digital-hw {
   type hw
   card 0
#  device 1
#  - Comment out "device 1" above and uncomment one of the below or create a
#    new "device N" line as appropriate for your sound card or
#  device 2
   device 4
}

# Control device (mixer, etc.) for the card
ctl.digital-hw {
   type hw
   card 0
}

# Direct software mixing plugin for analog output on the card
# Do not use this directly--it requires specific rate, channels, and format
pcm.dmix-analog {
   type dmix
   ipc_key 1234
   ipc_perm 0660
   slave {
     pcm "analog-hw"
     period_time 0
     period_size 1024
     buffer_size 4096
     rate 48000
   }
}

# Control device (mixer, etc.) for the card
ctl.dmix-analog {
   type hw
   card 0
}

# Direct software mixing plugin for digital (S/PDIF) output on the card
# Do not use this directly--it requires specific rate, channels, and format
pcm.dmix-digital {
   type dmix
   ipc_key 1235
   ipc_perm 0660
   slave {
     pcm "digital-hw"
     period_time 0
     period_size 1024
     buffer_size 4096
     rate 48000
   }
}

# Control device (mixer, etc.) for the card
ctl.dmix-digital {
   type hw
   card 0
}