UAC2 USB audio gadget/interface Rpi/XMOS suggestion

[rengartop]

Requirements:
USB to I2S IN/OUT (24bit/96Khz) UAC2 for Linux/Mac.

Any model of Raspberry pi work well as a usb audio interface?
Has anyone tested the latency issue? Is it easy to develop?
Any other alternatives? I hope so

A few years ago... I dedicated time to learning XMOS (it seemed like the only palpable alternative), and developed my first interface with XS1.
But over time this brand became a money sink...

 

[terryforsythe]

Any model of Raspberry pi work well as a usb audio interface?

I am using a Raspberry Pi 5, using USB C as the input, and outputting via USB A to a miniDSP MCHStreamer Kit. From the description: "MCHStreamer is a native 32/384kHz multi-channel USB audio to Toslink/I2S/SPDIF/ADAT/TDM/DSD/PDM interface - Converter mode for PDM to PCM (I2S) conversion"

In 2-channel operation the Pi's CPU load is very low, under 2%, so it is overkill and other Pi models probably will work well. It may depend on how many channels you need.

Has anyone tested the latency issue? Is it easy to develop?

I haven't heard about the issue, but check this thread: https://audiosciencereview.com/forum/index.php?threads/rpi-camilladsp-tutorial.29656/

Any other alternatives? I hope so

Probably, but I haven't looked. The Pi works well for my needs.

 

[rengartop]

I am using a Raspberry Pi 5, using USB C as the input, and outputting via USB A to a miniDSP MCHStreamer Kit.

Maybe I didn't express myself correctly.

PC/Mac -> USB to I2S
You are using the Raspberry as a PC/Mac... and the miniDSP as a USB to I2S device.

I want to use the Raspberry (or another alternative) as a USB to I2S device. (Exactly what miniDSP does.)
miniDSP uses XMOS...

 

[terryforsythe]

I don't know whether it can be done without adding additional hardware to it. I use the miniDSP, but you also can use a hat for the Raspberry Pi, e.g.,: https://www.hifiberry.com/shop/boards/dealing-with-blocked-p5-holes-9/

Why not just use the miniDSP MCHStreamer with your PC, and skip the Raspberry Pi altogether?

 

[aaa]

I'm wondering about this too. @terryforsythe, besides the miniDSP, what do you have connected to the RPi? Since you're just sending USB into the RPi and getting USB out of the RPi, why not skip the RPi entirely and go directly from the source into the miniDSP? Or are you doing some signal processing with the RPi?

On a semi-related note, I'm particularly curious about the possibility of using the HiFiBerry DAC8x hat with the RPi 5 as an audio interface between my iPad and my modular synth rig. Unlike most other DACs/audio interfaces, the DAC8x (and many of the other HiFiBerry DACs) have DC-coupled outputs rather than typical AC-coupled outputs, which makes it possible to send CV signals with high DC offset. There are plenty of iOS/iPadOS apps for sending CV signals through the regular Apple headphone adapter (which is also DC-coupled), but with the DAC8x I'm hoping to send 8 channels of CV instead of one.

My understanding is that the RPi 5 can be configured in a particular mode (called "gadget mode" I believe?) which turns it into a USB peripheral device. I think in this mode the RPi functions as a class-compliant USB device. But I'm not totally sure -- I'm looking for more information.

 

[phofman]

PC/Mac -> USB to I2S

So you need a device with USB input and I2S output. A few dedicated microprocessors can do that (XMOS, ATMEL, STM32). Also most linux ARM SBCs have the required hardware, only some support the hardware in their linux software.

IMO the easiest solution is RPi4 for 2ch (only 2ch I2S peripheral) and RPi5 for up to 8ch output. Quite a few threads on this topic here as well as on diyaudio.com - e.g. https://www.audiosciencereview.com/forum/index.php?threads/raspberry-pi-as-usb-to-i2s-adapter.8567/ , great guide on https://github.com/mdsimon2/RPi-CamillaDSP?tab=readme-ov-file#8-enable-usb-gadget-optional etc. etc.

 

[somebodyelse]

IMO the easiest solution is RPi4 for 2ch (only 2ch I2S peripheral)

I'd suggest the Zero for 2ch if the extra horsepower and memory isn't needed for something else like DSP. It's cheaper, and the much lower power consumption makes it more suitable for bus power.