[PD] I2S audio possibilities
Simon Wise
simonzwise at gmail.com
Wed Feb 4 17:58:44 CET 2015
On 05/02/15 02:34, Brian Fay wrote:
> Simon, have you compared the wolfson to any USB interfaces? I'm curious
> about how it performs by comparison, using no more than 2 input and 2
> output channels. I had some success with a USB interface on a Pi using pd
> and alsa, and got down to somewhere around 15 milliseconds of latency.
>
> I couldn't avoid occasional pops and clicks, and if I really pushed the
> number of effects I was using at once I would get some serious xruns. With
> the wolfson bypassing USB altogether, is it easier to achieve a low latency?
I have found that you really need to minimise everything to get the Pis running
smoothly, certainly no X and only what is strictly needed for control .. they
are not powerful devices but the access you have to GPIOs and such, and the
ability to program things at a low level means they can be made to do some tasks
well, and fast. The usb is to be avoided if at all possible, I'd like to test
the A model (with the single USB-OTG directly from the chip) it might be better
than going via that usb/ethernet chip, the A+ looks really compact as well.
I didn't need low latency, I got the wolfsons hoping for better quality analogue
I/O, their digital I/O options, the possibility of linking them clock-wise and
to avoid the endless usb hassles (there are other things I need the USB for!)
... they work well for this and I will do some serious testing but the audio has
been clean and sounding good so far ... and I have learnt quite a lot about the
various low level interface options.
>
> And since you mentioned an RT kernel, I'm curious - did you patch it
> yourself, or is there already an image available? Is it stable, or does it
> randomly freeze?
I didn't patch it myself, I have been using it in a dozen machines which now run
consistently ... I have been chasing some issue that was causing them to crash
after a while, replacing a pile of bash scripts and multiple calls to some
little dbus CL programs with the same thing directly from C in a pd external has
fixed the issue .. on the non-RT B+ system as well, so it probably was not
kernel related.
here are some notes I've made ... including instructions and links to the kernel
and files, and sources ... all on my dropbox, and the original link I used. They
are running notes from a project, so there is a bit of extraneous info but
download and install instructions are in there:
https://www.dropbox.com/s/1scwpdufk41k4es/04.setupWolfsonAudio.txt
Simon
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