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Re: Multiple audio ports

From: Paul Atreides
Subject: Re: Multiple audio ports
Date: Sat, 28 Aug 2021 14:50:49 -0400

This is definitely possible as I’ve done it with a Tascam US428 4ch usb Interface. A good place to start is to run the commands 
aplay -l [this lists your interface options]
alsamixer [which can I help you relate names  to interfaces as well]

They are usually sub indexed, something like 0,0 or  0,1
Depending on your configuration and what audio packages you have installed already, this can be a little bit of a jumping around game to figure out, but it will definitely work.

As far as the audio quality goes, I found some quirks with the ALSA System settings when you access them at a lower level. For example, on a built in laptop soundcard I was able to set the audio input to sample at 48 kHz from the flowgraph, but on a raspberry pi 2 with a USB audio input card I could only stream at 96K. The thing is, flowgraph would still run on the raspberry pi, it just sounded bad because of the mismatch between the flowgraph and hardware. 

If I remember correctly (bear in mind that it’s been a while and I’m pretty sure there is documentation somewhere in the GNURadio  docs for this) the syntax for audio cards has a relationship to how much of the intermediary driver you’re using (bare metal/kernel, simple system audio control, audio control with effects and routing)

I think the “hw:0,0” refers to the lowest level stream on the hard work hard, 
Whereas “plughw:0,0” I think goes through your operating systems internal Audio mixer. Then you elevate to pulse from there. 

In the end, for me, some of it was just a matter of figuring out what my hardware supported and trying different things. 
The good news is that a new USB audio card costs orders of magnitude less than a new USB Software Defined Radio!

Hope this helps!

<end transmission>

On Aug 28, 2021, at 14:12, Barry Duggan <barry@dcsmail.net> wrote:

I would like to make a flowgraph with two separate (independent) audio input ports and two separate (independent) audio output ports. Is it possible using Audio Source and Audio Sink blocks and/or using direct file I/O to /dev names (bypassing PulseAudio)? I've tried a scheme on two computers using ZMQ blocks, but the audio quality was very bad (I don't know why).

Barry Duggan KV4FV

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