[linux-audio-dev] question re: hammerfall cards

[Thomas Vander Stichele]

Hi Paul,

> in general, the best answer is typically:
> 
>    arecord -d plughw:0

Ok, so this is probably associated to the output of arecord -L then, which 
seems to be listing all "plugins" that can be used as pcm input ? I think 
I'm starting to understand slowly.  Is there some doc explaining output of 
arecord -L a bit more so I can follow what goes on, or is that an 
ALSA-specific question ?

> the "plughw" name allows to specify parameters (sample rate, bit
> depth, channel count etc.) that are *not* supported by the hardware,
> which is good because the hammerfall h/w supports *only* 26 channels,
> 24-in-32 bit samples, non-interleaved.

Ah, didn't know that - so you are saying that whatever you record, it 
always record 26 mono tracks at the same time ? So how do I tell arecord 
I'm only interested in the stereo S/PDIF signal coming in on ADAT1 ?

> not in the way that you are thinking of. there are substantial
> programs like ardour, ecasound and muse that can do this. arecord is a
> toy program, and should not be considered indicative of the toolsuite
> available for recording under linux. the problem is that nobody has
> felt the need to write a "simple command-line recorder". i think that
> the editors like snd, sweep, audacity and so forth will all allow you
> to do basic recording too, and i would recommend that you consider
> these. see www.linux-sound.org for more ideas.

I'll probably end up doing one in GStreamer for diagnostics purposes.  I'd 
imagine ALSA is great once it's set up correctly, but the setting up 
correctly bit is killing me.

> >b) what is the correct way (or a doc describing it) to specify devices for 
> >arecord ? 
> 
> you specify the name of a device that is defined in the ALSA
> configuration files, including your own ~/.asoundrc and the system
> one. 

Ok, so this is in addition to using the known set of plugins, as described 
above, right ?
I have the feeling that arecord should warn about incorrect device 
specifications, is it just not doing that or is there some reason not to 
tell the user that the device string is probably wrong ?

I'm asking about the correct way of device naming so that I can make sure 
that we (GStreamer) do it in the canonical way, because none of us is 
entirely sure about the right way of specifying a specific channel on a 
specific card using alsa.

> >c) could I have forgotten anything else here when trying to record stuff ? 
> >I assume that, since the Hammerfall doesn't have a mixer chip, the channel 
> >is always-on.
> 
> if the card is running, then data flows to the channel.
> 
> i don't keep much email around, and to be honest, i have forgotten
> what you were trying to do.

Something very simple - at first just trying to record an incoming S/PDIF 
signal coming from a DAT tape.  I've been recording with arecord and 
encoding with oggenc, because I know that oggenc uses very little bitrate 
when the signal is zero.  So that's my hacky test for "do I have incoming 
signal or not ?" :)

As you mentioned in the previous mail, I set my input for ADAT1 to Optical 
and I set the flag to true, so I must still be missing something else.

Thanks for your time,
Thomas

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