[PD] UDOO Quad and Generic Guitar to USB link issues

[Brian Fay]

The reason I suggested trying "arecord | aplay" is because it would be
running input and output simultaneously. In Audacity, you're doing one
after the other.

Unfortunately, I'm not sure exactly what is going wrong here. Does your
soundcard work as expected on other computers? Was it fine on the
BeagleBone Black?

On the Raspberry Pi, I'm running a multi-effects pedal, all built in Pd.
There's two parallel chains of processes, (each can run up to eight
effects). The effects I'm using are a looper, delay, waveshaper distortion,
flanger, granular synthesis (sort of limited implementation), reverb, and
EQ. I'm controlling things with a QuNeo MIDI controller and a push button
attached to the GPIO pins on the Pi.

By default, each of the eight effects in each chain are set to "bypass,"
which simply passes the signal onto the next effect. However, you can
adjust this on the fly for the effects to be whatever you want, so I can
set up something like:
Chain A: looper -> distortion -> flanger -> delay -> granular -> reverb ->
EQ -> bypass -> output
Chain B: delay -> bypass -> bypass -> bypass -> bypass -> bypass -> bypass
-> bypass -> output

I can independently control volume of each chain, so I could use Chain A to
build up some sort of droning ambience, and then solo over it using Chain B.

In practice, there is definitely a limit to the ability of the Raspberry
Pi. I think the example I just mentioned would probably run, but if I try
throwing too many effects on at once, (flanger, reverb, distortion, and
granular are all pretty intensive), I will start getting glitches - huge
crackles and jitters in audio. Turning off a few effects will stop the
glitches, but I all I can do to prevent them is to be conservative about
how many effects I turn on.

Just uploaded a little demo to Soundcloud of a recording I made with a
somewhat similar FX setup to what I mentioned. It was recorded with my
cell-phone, so it's a bit awful sound quality-wise (also really really
quiet, whoops...).
https://soundcloud.com/ovaltine-vortex/raspberry-improv

If you're curious about the patches and stuff, it's all here, but it's
hard-coded to MIDI values on the QuNeo and might be a bit confusing:
https://github.com/YottaSecond/thesisRepo


On Sun, Apr 6, 2014 at 2:37 PM, Carlos Sanchez <csanchez126 at gmail.com>wrote:

> Hey list,
>
> Thanks for your prompt replies and helpfulness!
>
> I could not get qjackctl to work, the audio will not go through and the PD
> CPU load gets abnormally high at around 67%...
> I had already played with the sample rate and I had noticed that
> augmenting the frequency yields better results but the noise was still very
> present.
> The sound card itself works correctly with Audacity so I am sure it would
> work with the arecord and aplay commands Brian suggested. Weirdly, it is
> only with PD that it is struggling...
>
> On a more encouraging note, as Brian suggested, it seems that the problem
> (or one possibility) is the duplex audio. I haven't thought about using the
> card as an output only device before and it did work! But afterwards, I was
> not able to change the settings back and use the noisy duplex audio any
> more, I was only able to switch the output devices...
>
> @Brian: What type of software are you using for the signal processing with
> the Raspberry Pi? I am very curious because I had first attempted to build
> this project on a BeagleBone Black but the heavy PD patches made it
> unstable or crash...
>
>
>
>
> On Sat, Apr 5, 2014 at 12:16 PM, Brian Fay <ovaltinevortex at gmail.com>wrote:
>
>> If you haven't tried it already, try increasing the latency in the audio
>> settings (probably not the issue, but worth a shot).
>>
>> Maybe it's only having trouble with duplex audio (simultaneous input and
>> output). Do you have both input and output enabled for your soundcard? Does
>> it work if you only have the output device set, and leave the input device
>> blank?
>>
>> You can test to see if duplex audio is working outside of pd - try
>> running "arecord | aplay" (the vertical bar means pipe the data from
>> arecord into aplay), and see if you get usable sound. You may need to set
>> some command line flags on those to get the sample rate and audio devices
>> right, sorry I don't know them offhand.
>>
>> I am running a fairly similar setup - for an honors project at my
>> university, I'm using a Raspberry Pi and Behringer UCG102. I have a nice
>> multi-effects pedal working at less than 20ms latency. If my Raspberry Pi
>> can handle it, I feel like your UDOO quad should definitely be able to. I'd
>> like to add that you have a nice taste in projects :)
>>
>>
>> On Fri, Apr 4, 2014 at 10:41 AM, Carlos Sanchez <csanchez126 at gmail.com>wrote:
>>
>>> Yes, I have tried changing sample rates and it has not solved the issue.
>>>
>>> The sound card I am using is basically a copy of the Behringer UCG102
>>> guitar to USB interface :
>>> http://www.behringer.com/EN/Products/UCG102.aspx
>>>
>>>
>>>
>>> On Fri, Apr 4, 2014 at 8:40 AM, tim vets <timvets at gmail.com> wrote:
>>>
>>>> and what is this 'Generic Guitar to USB' exactly?
>>>>
>>>>
>>>>
>>>> 2014-04-04 3:09 GMT+02:00 Carlos Sanchez <csanchez126 at gmail.com>:
>>>>
>>>>> Hello PD-list,
>>>>>
>>>>> I am currently working on my semester project which is a guitar
>>>>> multi-effect pedal using the UDOO Quad and PD. I got everything up and
>>>>> running on the Linaro Ubutu 12.04 LTS build provided by UDOO and I am
>>>>> having strange results with PD. The soundcard I am using works normally
>>>>> when I am using Audacity. It plays wav files and can record the guitar
>>>>> signal correctly but when it comes to PD, a basic osc object or a table
>>>>> read through ALSA produces a strange digital noise, completely ruining the
>>>>> audio signal.
>>>>>
>>>>> I have also tested this setup with a M-Audio Fast Track Pro USB card
>>>>> and the playback worked without issues, although I could not get the input
>>>>> signal through the adc object for an unknown reason.
>>>>>
>>>>> Has anyone tried a similar setup for guitar usage?
>>>>>
>>>>> Thanks!
>>>>>
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>>>>>
>>>>
>>>
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>>
>
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