[PD] audio output AND input with the Rpi?

[Chris Jack]

Hey folks,

Apologies as this post is not strictly about Pd, though Pd will be a
crucial part of my final setup so whatever solution I find ought to work
with Pd. Also, there is a chance the issue might lie with Pd. I just don't
know.

I'm looking for a usb bus-powered audio interface for the Rpi that can take
a stereo input and provide stereo output *at the same time.*
* *
I have tried a couple different images and a couple different audio
interfaces, to no avail. Perhaps there's something can be done with one of
these setups to get it working?

First, the Pd-LA custom Raspian (v1) image and Pd 43.2:

..with Behringer UCA202 (at 44100khz):

Alsamixer picks the device up but the input section shows nothing.

Pd (gui) audio preferences allows selection of the interface for both input
and output. Output only is lovely and clean but as soon as the device is
selected for audio input the audio quality drops horrendously (vaguely
recognisable from the original signal)..
..although what gives me hope is I CAN software monitor the input (poorly)
in 'Test Audio and MIDI' with this arrangement.

..with Behringer UCA202 (at 48000khz):

Output only in Pd is poor (beating and popping sound - possibly sounds like
a samp rate conversion issue).
When device is selected as Pd input software monitoring is possible and
oddly, though the result is still poor, there is effectively no drop in
quality from having the device selected only for output and the monitored
signal sounds drastically better than at 44100khz.


..with Turtle Beach Amigo II* (at 44100):

Alsamixer shows both input and output and allows to change gain of both.
If plugged in from boot and only the output is selected in Pd it works but
with a lot of jitter. Selecting the device for input too causes a further
drop in audio quality although again I can software monitor the input in
'Test Audio and MIDI'
If plugged in after boot the OS crashes.


The Satellite CCRMA (operating via ssh) and Pd-extended:

..with Behringer UCA202 (at 44100 and 48000):

Alsamixer picks the device up but again the input section shows nothing.

If I have the device plugged in from boot then I get the same behaviour
with it as I do in Pd vanilla on the Pd-LA Raspian image, ie. software
input monitoring but at an extremely poor quality.

If I don't plug the device in from boot I see it in Pd audio prefs but get
this:

ALSA input error (snd_pcm_open): No such file or directory

ALSA output error (snd_pcm_open): No such file or directory

from the Pd terminal and this

ALSA lib pcm_hw.c:1401:(_snd_pcm_hw_open) Invalid value for card
ALSA lib pcm_hw.c:1401:(_snd_pcm_hw_open) Invalid value for card
oops: ALSA cards not reported in order?

from the ssh terminal.


..with Turtle Beach Amigo II* (at 44100khz):

Alsamixer shows both input and output and allows to change gain of both.

If plugged in from boot and then only output selected in Pd I get clean
audio out. If I try to select the Turtle Beach as audio inout in Pd then Pd
stalls indefinitely when I try to 'Test Audio and MIDI' or make anything in
a patch.

Same direct input monitoring by default.

Also get

ALSA input error (snd_pcm_open): Device or resource busy

ALSA output error (snd_pcm_open): Device or resource busy

from the Pd terminal if I don't have it plugged in from boot, though no
message in ssh terminal.

*It also appears that by default the Turtle Beach does direct input
monitoring of some sorts, the output stage sending out a clean copy of
whatever signal is going into the input stage whenever the device is
plugged into a usb port. With the Pd-LA image this occurred simultaneously
while input monitoring in Pd. I guess this is part of the design of the
Turtle Beach, though their documentation is devoid of any useful info
regards this. If this is the case then this ain't the sound card for me,
though clearly some might find this a very useful feature.

Just to give a bit more info about what I'm attempting: I wish to run the
stereo input from the Turtle Beach through Pd, play with the audio signal
using data from an accelerometer (not nearly there yet) and then send the
audio out through the Turtle Beach's stereo output.

Apologies for the essay. Hopefully my findings are useful for others and
hopefully I can get my rig working! Help muchly appreciated. I've probably
left out some crucial bit of info so please shout me if I have!

Cheers,
Chris Jack.

Chris Jack

*art/research*
http://itsmrjack.com/

*discus jockeying/sound art*
http://soundcloud.com/itsmrjack/
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