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SP/DIF Digital Audio {DA} out.
http://forum.linhes.org/viewtopic.php?f=2&t=4675		 Page 1 of 1
Author:  linuxgeek [ Mon May 23, 2005 1:01 am ]
Post subject:  SP/DIF Digital Audio {DA} out.
Hi All.

Ok I am having some issue with Audio and I need some clarification.

When using DA only where does volume come into play?

Also how is the sound captured?

The sound that I can hear sounds like its a bit maxed out
as in 100% and needs to be reduced.

I cannot find any volume controls for DA.

I want to use DA only.

In mythtv it is set for ALSA:digital and internal volume
controlled is off/unchecked {no volume control in Mythtv
enabling this causes myth to not find the audio devices.}

One more thing not sure how to get the digital data from the HDTV
card which I presume is AC3 as I would get from a DVD that is. I do
get sound the same as I do from the PVR-500's. As in analog to digital.
Of course that is my speculation.

PCM = Digital stream?

Any ideas?

Here is my current /etc/asound.conf {found this one on a another
forum and made some changes for my environment}

# 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).
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"
}

# Alias for analog output on the (hw:0,0)
# - 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
pcm.analog {
type plug
slave.pcm "analog-hw"
}

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

# Alias for (rate-converted) mixed analog output on the
# (hw:0,0)
# - This will accept audio input--regardless of rate--and
# convert to the rate required for the dmix plugin
# (in this case 48000Hz)
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 (rate-converted) digital (S/PDIF) output on the
# (hw:0,4)
# - 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 (rate-converted) digital (S/PDIF) output on the
# (hw:0,4)
# - 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 (hw:0,0)
# Do not use this directly--it requires specific rate,
# channels, and format
pcm.analog-hw {
type hw
card 0
device 0
}

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

# Alias for digital (S/PDIF) output on the (hw:0,4)
# Do not use this directly--it requires specific rate,
# channels, and format
pcm.digital-hw {
type hw
card 0
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 (hw:0,0)
# Do not use this directly--it requires specific rate,
# channels, and format
pcm.dmix-analog {
type dmix
ipc_key 12345
ipc_key_add_uid true
slave {
pcm "analog-hw"
period_time 0
period_size 1024
buffer_size 32768
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 (hw:0,4)
# Do not use this directly--it requires specific rate,
# channels, and format
pcm.dmix-digital {
type dmix
ipc_key 10246
ipc_key_add_uid true
slave {
pcm "digital-hw"
period_time 0
period_size 1024
buffer_size 32768
rate 48000
}
}

# Control device (mixer, etc.) for the card
ctl.dmix-digital {
type hw
card 0
}
Author:  kebe [ Mon May 23, 2005 6:43 am ]
Post subject: 
Digital audio out is used with an external amplifier of some type (usually with a Dolby decoder to decode the AC3 from DVDs).

You control the volume with the external amp.

Your PVR-500 will capture the TV audio signal and put it in the mp2 file. Your sound card is only used for playback.
Author:  linuxgeek [ Fri May 27, 2005 7:31 am ]
Post subject: 
Thanks for the reply...

I know how to connect this to my receiver. I need to know how volume
is set during the capture/playback. I need to how to lower that setting.
I believe it is maxed out and/or overdriving and needs to be lowered.

I am getting a ringing sound during playback and live TV.

I am trying to understand if the PCM stream out if it can be altered.

Is there any jitter control?

Digital out is digital out... I find it hard to believe one can be better then
another. In this case sound card wise. Of course I am not sure of that
statement I am no audio expert. But it would seem that Digital would
be the same no matter the device.

My Mythtv is almost ready to use now.. My only issue is the audio.

I am currently using the coax sp/dif out.

Any ideas?
Author:  tjc [ Fri May 27, 2005 9:10 pm ]
Post subject: 
Check what audio chip it thinks you're using. The intel 810 (i810) only has two PCM "volumes" i.e. on and off... A lot of "chips" (for example the one on my Nforce2 based MoBo) will work using the i810 driver so you end up with lowest common denominator limitations in the software. If you're using that driver and your chip is more capable you may want to switch.

Sorry if I'm explaining this badly, but it's been a long week and I'm very overtired...
Author:  Xsecrets [ Sat May 28, 2005 12:12 am ]
Post subject: 
also I belive the recording volume you are looking for is going to be in your drivers for the tvcard. I know you can control the recording volume with ivtvctrl for ivtv drivers. I'm sure bttv cx?? etc have similar utilities.
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