The xmos is just the microprocessor used for USB interfacing, by itself you can't tell if a device will have decent or better jitter performance, it is just one piece in the processing/interfacing. Inherently it has no jitter specification. That's up to the device/DAC implementation.
True, but all reviews of dacs made by amirm that have the xu208 chip ( more than 10 ! ) shows, without exeption, similar excellent jitter measurements, so maybe many manufacturer uses the same implementation and programing of the xmos xu208 ? There is a pattern here that cant be ignored.
Amirm has also tested older dacs that dont use the xu208 chip but have less good USB solutions , and almost all of them shows very bad performance with the USB connection.
An example tested is here , a dac and earphone amplifier from 2005 that measures well with analog input but very bad with the USB input.
This is a review and detailed measurements of the Meier Corda Aria DAC and headphone amplifier. It is on kind loan from a member. It is an older product, introduced around 2005 I think. Not sure how much it cost then. The Aria gives the impression of a "high-end" product: As you see, it is a...
www.audiosciencereview.com
The SMSL D300 spec has this information about the xu208:
XMOS XU-208 USB Interface
The USB-B input of the D300 embeds a XMOS XU-208 32bit chip. It allows the decoding of USB audio streams and offers a nice audio precision. Associated with the ROHM DAC, it allows the D300 to read high resolution streams, up to 32bit 768kHz PCM and native DSD512.
The USB 8 kHz packet noise must be minimized to, and the xu208 is excellent at that.
”USB data transmission occurs in bursts every 125 μs. With the arrival of each such packet, the receiver will draw more power while creating a burst of high-frequency noise. The increased power draw can/will result in a corresponding dip in voltage. Without sufficient regulation, this dip will be seen by the DAC chip and end create an 8 kHz ripple in the output. Increased ground currents can also create voltage fluctuations at the DAC chip with the same effect. Another possibility is that aforementioned noise from the USB receiver gets into the analogue circuits through parasitic coupling where it is demodulated, again creating an 8 kHz tone.”
Read more here :
TLDR: PC as my source, Massdrop SDAC, no music playing, volume set to 100%, noise floor measurement, how do I get rid of this 8kHz spike? Some history: I bought my first external DAC, SMSL SU-8, this past summer and while it was a huge update over my existing equipment in terms of sound...
www.audiosciencereview.com