Massahwahl
Posts: 1
Joined: Sat Jan 12, 2019 2:25 am

Capturing multiple audio inputs

Sat Jan 12, 2019 2:46 am

Hoping to get some insight into how to pull off a project I am hoping will be possible with an rpi3. I have a modded Korg Volca Beats drum machine that has 5 audio outputs for individual drum sounds as opposed to the standard output that mixes all the channels together. I am wanting to create a way to take all the inputs if possible or at the very least two of them, apply effects and then output it to my mixer. Software wise I know this is possible but is there a way to wire the volcas individual outputs to the pi? I found a few audio hats but was not sure which one would be the best fit to do this. Any help is appreciated!

wh7qq
Posts: 1299
Joined: Thu Oct 09, 2014 2:50 am

Re: Capturing multiple audio inputs

Sat Jan 12, 2019 8:41 pm

You should look at the AudioInjector web site (www.audioinjector.net)
, for the "Octo Soundcard". Support has been a bit scanty of late but their forum has been pretty helpful. I have the basic stereo card and I am currently having problems getting it to work from Raspbian Stretch...it previously worked well from Jessie and I should have left well enough alone but... Previously, the Stereo card worked fantastically for ripping old vinyls to .wav files.

On their web forum, "flatmax" has indicated that there may be a problem with the current RPi kernel and recommends going back to an earlier edition. I am not sure if this is my problem with it and will investigate further. "flatmax" (forum moderator) has apparently been MIA from the forum for about 6 months but is back now with a Jan. 7. 2019 post and a new Amazon Store page has sprouted as well, with a much pricier Ultra 2 card for sale.

mhelin
Posts: 125
Joined: Wed Oct 17, 2012 7:18 pm

Re: Capturing multiple audio inputs

Wed Jan 23, 2019 8:52 pm

You better try USB audio interfaces. Multichannel interfaces arent cheap though. Get an USB hub and three similar cheap USB-interfaces - usually called "USB Sound Card" in Ebay - which work from the USB clock in synchronous mode. Connected to the same USB port via hub they keep in sync. That of course depends on the chip set. AFAIK, the common "3D SOUND" adapter should work:

https://www.ebay.co.uk/itm/USB-To-3-5mm ... 2519834545


wh7qq
Posts: 1299
Joined: Thu Oct 09, 2014 2:50 am

Re: Capturing multiple audio inputs

Thu Jan 24, 2019 6:26 am

I subsequently have ironed out my problems with the AI Stereo on Stretch. As a result of a use hiatus...6 months or so... I screwed up the alsamixer settings. It is working like a champ now...perfect recordings from my vinyl and cassettes. It was all my fault and none of the AI Stereo Card's.

The "Octo" 8 channel card is going for $58 US on Amazon...pretty cheap for what it is, not something the average user would want or need. I don't think there are any multi-channel recorders on the market for such a price.

mhelin
Posts: 125
Joined: Wed Oct 17, 2012 7:18 pm

Re: Capturing multiple audio inputs

Thu Jan 24, 2019 12:28 pm

wh7qq wrote:
Thu Jan 24, 2019 6:26 am
The "Octo" 8 channel card is going for $58 US on Amazon...pretty cheap for what it is, not something the average user would want or need. I don't think there are any multi-channel recorders on the market for such a price.
There are channel swapping problems with Octo reported on their forum. Pi's I2S/PCM interface is a little bit unreliable at least in frame sync slave mode, and the PCM interface may miss a sample when the recording is started. Also a FIFO overrun may cause this problem. I think Octo uses some extra GPIO pin(s) to help with the sync when the recording is started but looks like it's not bullet proof method they use. You got to remember many of the RPi HAT products including audio add-ons are designed by hobbyists who simply don't have the experience of pros.

To make a multi-channel audio interface like Octo fullproof you must use some kind of software processing for the audio samples and use some frame markers at some LSB's of the 32-bit sample word (audio takes usually at most 24 bits so there is 8 bits left for user). That would obviously increase the latency and CPU% but it would at least work.

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