Thank you for your reply.
My apologies for how long this is getting.
Amongst all the stuff in my original post, I forgot to describe two
important things:
Debian wheezy.
uname -a:
Linux medea 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2 x86_64 GNU/Linux
ALSA version:
Advanced Linux Sound Architecture Driver Version 1.0.24.
On 13-06-06 00:06 , Clemens Ladisch wrote:
> Tom Rushworth wrote:
>> I'm trying to get high resolution digital output from the following setup:
>>
>> Output of aplay-L:
>> ...
>> default:CARD=PCH
>> HDA Intel PCH, ALC892 Analog
>> Default Audio Device
>> ...
>> iec958:CARD=PCH,DEV=0
>> HDA Intel PCH, ALC892 Digital
>> IEC958 (S/PDIF) Digital Audio Output
>>
>> Notice that:
>> A) Both the iec958 and hdmi show as DEV=0 but the /proc/asound
>> information shows them to be devices 1 and 2 respectively.
>
> Those are different abstraction levels.
> "iec958:0" is an alias for "hw:0,1".
Ah. I hate standing at the bottom of the learning curve looking up :).
>
>> B) There is no plughw device of any sort.
>
> That is not the kind of device shown by "aplay -L".
OK, I guess I'm misunderstanding something. What led me to look for it
in the "aplay -L" output in the first place was a sample of someone
else's output that showed a device named plughw:
------------------[
....
iec958:CARD=Intel,DEV=0
HDA Intel, AD198x Digital
IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=Intel,DEV=0
HDA Intel, AD198x Analog
Direct sample mixing device
dmix:CARD=Intel,DEV=1
HDA Intel, AD198x Digital
Direct sample mixing device
dsnoop:CARD=Intel,DEV=0
HDA Intel, AD198x Analog
Direct sample snooping device
dsnoop:CARD=Intel,DEV=1
HDA Intel, AD198x Digital
Direct sample snooping device
hw:CARD=Intel,DEV=0
HDA Intel, AD198x Analog
Direct hardware device without any conversions
hw:CARD=Intel,DEV=1
HDA Intel, AD198x Digital
Direct hardware device without any conversions
plughw:CARD=Intel,DEV=0
HDA Intel, AD198x Analog
Hardware device with all software conversions
....
------------------]
Even more specific is the page at:
http://users.telenet.be/on4qz/faq.html
which shows aplay -L output from a machine that seems to have exactly
the same motherboard sound card I have, and which also shows a plughw
device:
------------------[
....
plughw:CARD=PCH,DEV=1
HDA Intel PCH, ALC892 Digital
Hardware device with all software conversions
....
------------------]
>
>> device "plughw:CARD=PCH,DEV=1"
>>
>> This works well with CD format .flac files (even though there doesn't
>> seem to be a plughw device), but is completely silent when I try to
>> play a 192/24 .flac file. The /proc/asound/PCH/pcm1p/sub0/hw_params
>> file shows:
>> ------------------[
>> access: MMAP_INTERLEAVED
>> format: S32_LE
>> subformat: STD
>> channels: 2
>> rate: 192000 (192000/1)
>> period_size: 2048
>> buffer_size: 8192
>> ------------------]
>> and 32-bit is not supported by the hardware,
>
> Why do you say that? The above shows that the hardware is using
> a 32-bit format.
Because I don't understand what I'm talking about? :) I thought that if
the codec#0 and the mfg spec both omit 32bit as a capability that the
chip wouldn't support it, but I had not considered that the specs might
be talking about the output jack side while the hw_params file was
probably talking about the HDA interface side.
>
>> The /proc/asound/PCH/codec#0 file contains:
>> ...
>> PCM:
>> rates [0x5f0]: 32000 44100 48000 88200 96000 192000
>> bits [0xe]: 16 20 24
>> ...
>> which seems to agree with the manufacturers specs for the ALC892 in
>> indicating that 192/24 should be OK
>
> Please note that the format of samples in memory is not the same as the
> format output at the S/PDIF jack. In-memory samples are padded to
> 32 bits to make it easier for hardware and software to handle them.
Which makes good sense. I need to read a bit more of the HDA spec to
see if the stream examples they show are on the computer side or output
jack side of the chip I guess. Skimming the pictures isn't enough :).
>
>> if I can convince alsa to produce it.
>
> Your information shows that the device is successfully playing 24 bits
> at 192 kHz.
All except for the sound at the end :).
>
> Are you sure that your receiving device (whatever it is) can actually
> handle this format?
It's a Schiit Bifrost DAC:
http://schiit.com/cart/index.php?main_page=product_info&cPath=0&products_id=7
and the web page specs claim 192/24.
I have no instrumentation capable of looking at the S/PDIF stream and
telling me what it really is, but I have run the DAC using the Decibel
player on a Mac Pro Desktop and the Mac's S/PDIF output.
http://sbooth.org/Decibel/
The same test .flac files that produce silence on my Linux machine
produce excellent sound on the Mac. (I do realize that without actually
instrumenting the S/PDIF stream all I have is hearsay claims, but I
thought they were pretty convincing :). One of the major reasons for
this whole exercise was to see if I could hear the difference with my
own ears...)
>
>
> Regards,
> Clemens
>
Thanks again for taking the time to reply.
Your comments don't give me the answer yet, but they do give me new
directions to investigate :). In particular, since one of the links
above shows alsa recognizing the HDA Intel PCH motherboard sound card
and my version of alsa doesn't recognize it, I think my best bet is to
move to the most recent version of the kernel and alsa that I can and
then look at the alsa/aplay source to see if I can understand exactly
what the numbers mean.
Regards,
--
Tom Rushworth
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