RPi and USB DAC's vs. I2S

Is it true that the RPi with Volumio has limited capacity over the USB bus for USB DAC’s? That is to say, are USB-DAC’s not really suited for the RPi? (vs. I2S Dac’s)


R-pi has some issues with the USB\Ethernet BUS. It just cannot handle high bandwiths, so this result in some cases in dropouts and noises.
i2s is definetely the way to go:

-Less jitter prone
-Avoidance of USB issues
-Less signal chain

i2s dacs give other benefits too…

192/24bit support
better physical connection
easier to put in a case
free up a USB socket


Pi ver B - Volumio 1.4.1

I’ve been using the USB via an HiFace M2Tech USB/Coax Converter connected to my Marantz 7701 PreAmplifier.

I recently got an HifiBerry Digi instead (i2s --> optical) and the difference was big.

With USB I was struggling with 24/192, they now play without problems. And foremost I have a significant improvement of the sound quality, even though it was definitely not bad before. It’s moved up as couple of notches on the ladder and is clearer and more detailed.


Note. I have limited experiences with different DAC’s and my ear needs comparative listening so take my comments for this limited case.

Can anyone second this?

Does the USB port not support 192khz/24bit?

USB audio is driven by the PC market.
Windows doesn’t support HD audio internally and the majority of USB dac providers therefore don’t use devices which deliver such features due to cost. MacOS and Linux can support USB HD audio and there are non-Microsoft USB audio drivers which deliver full HD audio support too.

The whole thing is difficult for someone buying a $2 USB audio card to know what it supports. Certainly the Meridian USB dac is a TI PCM5102 192/24b capable DAC for example but you’d be better buying a similar DAC on the I2S interface and doing away with all the “middle” bit of conversion to USB and congestion back to I2S.

Yes I agree that RPi Ethernet & USB does have some actual bandwidth Issues.

If we take at the max theoretical bandwidth point of view of the comms protocols we are talking about
USB2.0 = 480 Mbit/s
ENET100 = 100 Mbits/s
i2S on RPI = approx 20 Mbits/s

To play 24bit/192kHz we need to guarantee 9 Mbits/s.

There are several posts on the Internet that indicate that max bit rate with RPi Ethernet comms in one direction is approx 30 Mbits/s.
I don’t think anyone will claim that the USB ports on the RPi can deliver anywhere near 480Mbits/s
It seems also that the ENET and USB intefaces share the same bus (the Enet is bridged from the USB bus connected to the limited performance processor). Mixing up the Enet and USB bus power and comms can’t be a good thing and could lead to unpredictable results when multiple devices are connected to the RJ45 & USB Ports.

This leads me to conclude that i2s single node implementation is clearly the better option (as the i2s RPi DAC’s are doing) will achieve the required bandwidth (with approx 50% to spare). In testing I haven’t had any issues with the 2 i2s DAC’s that I have tested.

By the way I am not slating the RPI, they are worth every penny that I have paid for them. I don’t think that putting 4 USB ports on the RPi B+ was a particularly good idea. We are all guilty of sticking things into empty sockets !!!

I like the idea that a 1986 low bandwidth serial bus does the job coupled with RPi GPIO. Well done to the team of people who ended up beating the marketing crap and coming up with a working and reliable solution. For me the RPi & i2s DAC’s give fantastic sound quality per penny spent.