DIY synth building and hacking is increasingly popular. The PISound interface from Blokas aims to provide you with pro ins and outs for your Raspberry Pi system.  
The Raspberry Pi 3

What is it?

pisound (top and bottom view)

Setting It Up

Attaching pisound to Raspberry Pi
pisound installed on Raspberry Pi, and being recognized as an audio interface

Trying Things Out

Testing Audio 

Building a Synth

Building an FX Unit

The Pure Data delay FX patch
Connecting to the pisound Wi-Fi hotspot on an iPad, and setting up the TouchOSC MDI Bridge settings

pisound vs. USB Interface


Liam is the Head Of Development specialising in software development at Modal Electronics, the company behind the 002, 008, CRAFT and SKULPT synthesisers, and was previously the lead software developer at nu desine, the developers of the AlphaSphere MIDI controllers. He was also an Associate Lecturer at UWE, Bristol, UK where he gradua... Read More


aaron p
would it be fair to say that this I2S audio interface provides lower jitter than any USB audio interface will?
(clock recovery notwithstanding...)
i would think that such a "direct drive" approach would lead to lower latencies and jitter overall, as the I2S master clock is a function of the audio sample rate...
The jitter is the consequence of the variations in clock signal, which is used in ADC/DAC. In pisound the master clock is a on-board crystal with a maximum jitter of 1ps (that is really low!!!). And in USB audio interface it depends on USB transfer type. As far as I know, there three types of USB cards:
- uses isochronous transfer and audio clock is derived from USB transfer clock;
- uses bulk transfer and separate oscillator to generate audio clock;
- uses isochronous transfer and re-clocks the USB transfer clock for audio.

The second group has the lower jitter than other two (comparable to the pisound), but introduces other problems. More on that:
The third group is kind of rare and very pricey, however it should have less jitter than the first one.

So long story short - yes, pisound has less jitter than the most of USB audio cards.
You're right, the I2S on Raspberry Pi's Broadcom processor is implemented as a dedicated peripheral meant for audio communication with external audio DACs / ADCs / codecs, and it doesn't have to share the bus bandwidth with any additional devices as in USB's case, so it already has an advantage. Furthermore, on pisound, the I2S communication is controlled by the ADC chip, clocked using a dedicated external crystal clock source, leaving the processor less chances to get the timing off. :)
Yes, you are right! In Raspberry Pi's Broadcom processor, the I2S is a dedicated peripheral purely dedicated to dealing with ADCs, DACs or Audio Codecs, unlike for USB controller which needs to multiplex the communication with multiple devices. In addition to that, the I2S communication on pisound is driven by an external crystal oscillator attached to ADC as master, so there's even less chances for the audio timing to stray off. :)

Want to join the discussion?

Create an account or login to get started!