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? 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? -Brian On Wed, Feb 4, 2015 at 9:43 AM, Simon Wise <[email protected]> wrote: > On 04/02/15 05:30, Miller Puckette wrote: > > In an ideal world someone would build us an I2S expansion board for Pi >> with 8CH audio in and out, memory mapped straight to user space. Maybe >> someday someone will build that :) >> > > the wolfson cards have some of that, and quite a bit of control > internally, with lots of sync possibilities and so forth, even programmable > dsp routines if you really want! The drivers supplied are for alsa and work > fine with pd, and expose their internal mixing options etc in the alsa > interface ... but the Pis don't expose the 8ch I2S on their pins, only 2ch > ones, so though the wolfson card can take 8ch in the pi can't deliver it > ... I guess the 8ch I2S interface is going to the hdmi circuitry. > > The B version uses almost every available pin, including the extras in p5, > but the B+ version doesn't need all the new ones. > > I can put an image up on dropbox of a system for the B version with the > modules, scripts etc working nicely, and an RT kernel, if that is useful, > that has been well tested. The images on the wolfson site were not working > for me, but I found a version that worked. I haven't got a B+ wolfson card > so can't verify them. > > One issue for me is that I'd like to play the audio from AV files through > them, but the players I am using send audio directly out, and I am not able > to send it to userspace, alsa and pd ... so can't use the wolfson audio in > those cases. > > It should be possible, for example, to daisy-chain several pis with > wolfson cards via the wolfson SPDIF I/O ... then the clock source can be > all from the first wolfson, and the SPDIF chain ending up with a digital > stereo mix output from the last wolfson, all the mixing and clocking > options are available via alsa. Testing that is next on my list. > > > Simon > > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> http://lists.puredata.info/ > listinfo/pd-list >
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