JACK, DC signals, pinouts.

[widdly]

I plan on making a raspberry pi module for a modular synth and I have some questions...

Is anyone using the JACK daemon with an octo sound card? Any issues? I plan on running netjack on the Raspberry Pi and accessing some of the audio streams on a PC via an ethernet connection.

Is the soundcard capable of passing DC signals? Being able to pass DC signals is very useful in a modular synth since the inputs/outputs can be used for Audio as well as Control Voltage (LFO's, ADSR, Sequencers etc.) or gate signals.

Also is there a pinout for the octo? I would like to use it without the rca or balanced output options. I would like to boost the outputs to +/- 5v using opamps and attentuate the inputs from +/-5v down to a suitable input level using a pair of resistors.

[flatmax]

Hi there,

Yes - you can go to DC if you use the headers directly ... you may want to use the RCA boards as a starting point and remove the DC decouplers :
https://github.com/flatmax/AudioInjector.Octo.RCA
https://github.com/flatmax/AudioInjecto ... CA.sch.pdf

You could also short out the Electrolytic DC decoupling caps on the RCA output board if you like !

Oh and the balanced version is here :
https://github.com/flatmax/AudioInjector.Octo.balanced

Jackd should be all good and working.

Matt

[widdly]

Thanks Matt. Looks like it will be ideal for my project.

[nettings]

Using jack2 here without issues, and also a network audio connection with zita-njbridge (not netjack). All well, except somehow the card gets opened with 8 inputs rather than 6. Still investigating.

[nettings]

Hmm. The kernel driver thinks the card has 8 ins:

Code: Select all

static int audioinjector_octo_startup(struct snd_pcm_substream *substream)
{
	struct snd_soc_pcm_runtime *rtd = substream->private_data;
	rtd->cpu_dai->driver->playback.channels_min = 8;
	rtd->cpu_dai->driver->playback.channels_max = 8;
	rtd->cpu_dai->driver->capture.channels_min = 8;
	rtd->cpu_dai->driver->capture.channels_max = 8;
	rtd->codec_dai->driver->capture.channels_max = 8;

(from https://github.com/raspberrypi/linux/bl ... oundcard.c)

Matt, is this intentional or a typo?

[widdly]

I'm having issues with the channel assignments changing when restarting jackd. Using the rca board, the first channel output is on the far right connector and sometimes on the far left other times. I wonder if that behaviour is related.

What parameters are you using for jackd? Do you specify channel counts and sample size?

[nettings]

I've seen that once after a JACK crash. I guess the trouble is that you're piping all those channels through a single wire, interleaved. If you somehow start counting at the wrong time, you'll get garbled channel orderings. That should be a driver issue.
Even simpler I²S interfaces sometimes come up with swapped left and right channels if the timing is not robust.

Reminds me of old, old DMX interfaces missing the start sequence. Does wonders to a tired old light show

[flatmax]

Hmm. The kernel driver thinks the card has 8 ins:

Code: Select all

static int audioinjector_octo_startup(struct snd_pcm_substream *substream)
{
	struct snd_soc_pcm_runtime *rtd = substream->private_data;
	rtd->cpu_dai->driver->playback.channels_min = 8;
	rtd->cpu_dai->driver->playback.channels_max = 8;
	rtd->cpu_dai->driver->capture.channels_min = 8;
	rtd->cpu_dai->driver->capture.channels_max = 8;
	rtd->codec_dai->driver->capture.channels_max = 8;

(from https://github.com/raspberrypi/linux/bl ... oundcard.c)

Matt, is this intentional or a typo?

Intentional ! There is no simple way to tell ALSA to only use 6 ins and 8 outs

Matt