Cirrus Logic + Pi 2 = Latency?

Hey all,

Just wanting to get an idea of the round-trip audio latency we might expect from the Cirrus Logic audio card on a Raspberry Pi 2, in particular when running PureData as an audio effects processor for 2-channel full-duplex audio (assuming we configure it for stable operation with a moderate level of processing complexity)?

In particular, how does the Cirrus Logic card compare to other Pi 2 audio solutions out there, for example USB audio interfaces, in terms of audio latency? I'm trying to decide whether to get a Cirrus Audio card, or go for a USB interface. (Super high quality audio isn't hugely important to me at this stage).

I know all the above is affected by OS type, kernel tweaks etc, so I'd be interested in how you approach these aspects too...

Thanks,

Sal

Former Member over 10 years ago

Hi Sal,

USB and the Cirrus Logic don't differ that much when it comes to system latency. Both solutions don't run very stable when using lower values than 64 frames per period. So with a sample rate of 48kHz this would yield a system latency of 2*64/48000=2.7ms (the 2 comes from the minimum number of periods ALSA accepts). When it comes to round-trip latency the Cirrus Logic beats USB as the USB driver adds at least one period (so in our case 64 frames, so 1.3ms) to the output buffer while the output latency of the Cirrus Logic is below 0.3ms. So if you really want to achieve the lowest possible latency with a Pi I'd go for the Cirrus Logic.
In order to be able to do real-time, low-latency audio you can find some tips here: http://wiki.linuxaudio.org/wiki/raspberrypi
One of these days I'll add a paragraph about the Wolfson/Cirrus Logic audio interfaces to that article.

Jeremy
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