I have this curiosity about i2s which I’ve played around with for a little while, having built an i2s streamer mentioned elsewhere using a Pi4 and FifoPi and HDMI Pi from Iancanada. Along with that, I also played with a Breakout box that takes HDMI and outputs various standards including PS compatible i2s.
So within the past couple weeks, I also got my hands on the Douk, then got a deal on a used Matrix. So here’s my observations so far.
Both have no problems outputting PCM properly.
The Douk has a constant signal on pin 15 that sets the pre-emphasis/de-emphasis flag, which only affects 16/44.1. This can be eliminated by pulling or covering pin 15 from the HDMI cable, or cutting the trace between pin 45 of the XMOS chip and pin 15 of the connector - It’s a direct connection between the pin with no resistor in the path, and the trace is easily accessible.
The Douk also reverses L+R channels with DSD. This is verified with a bunch of free test files I have that comes in various bit/sampling rates in both PCM and DSD, so you can easily here the channels reversing on DSD (it opens with a piano spanning both channels). It does fine with PCM/Flac.
The Matrix has no swapping problem on DSD, and does not set the pre-emphasis flag,
The Douk has no problem running off USB power (it has the ability to be externally powered).
The Matrix DOES draw significantly more current than the Douk. The first clue I noticed was that the USB B connector was 3.0, which has a 900ma standard compared to 2.0 which has a 500ma standard. Along with that, they spec that if using an external supply, it needs to be at least 6 volts and 800ma. So when it downconverts internally to 5v, it will likely be near the 900ma spec.
When I tried plugging it in to my Pi streamer, I got a low voltage warning from the OS. I have been running the Pi (with hats) through the Iancanada FifoPi rather than the USB C supply input because that’s been sufficient, and the FifoPi cleans the power somewhat. But the powering the 5v through the FifoPi limits the total 5v power to 2A. That may have been fine with older Pis that only had USB 2.0 ports, but the Pi4 has 2 USB 3.0 ports. I upped the output of my external 5v to 5.23 volts to account for the sag, and no more low voltage warning. I’m going to power the 5v directly through the GPIO and bypass the FifoPi, so that should take care of it - or maybe I’ll use a spare 12v external I have along with a buck converter to bring it down to 6 - maybe.
There’s no such problem with my music only Windows PC with “normal” USB 3.0 ports. Depending on your computer/streamer/whatever, you may want to be cognizant of the higher current needs (which exceed the normal 2.0 spec), or as with many users, just power it externally.
Edit: I haven’t gotten around to measuring the actual current draw of the Matrix yet. If anyone has tested the actual draw, please post the number (so I don’t have to dig my stuff out).