Great work! Any chance to get a jitter test and an FFT with this "cable"?
To elaborate on what KSTR said, for USB, most of the devices we care about at ASR work in the asynchronous UAC mode. Unlike SPDIF, this doesn't transmit the audio clock with the data. At a high level, flow control is achieved via feedback of a value to the host, indicating if it should speed up or slow down to ensure that the buffer in the device doesn't under or overflow. Data gets clocked out of that buffer by locally derived clocks. Since data is clocked out with a local clock, any jitter on the USB interface doesn't matter at all up to the point where USB data transfer stops working.
Amir still does the J-Test, but it's sort of looking at higher order effects. I'm not sure I would say it measures jitter over an asynchronous USB interface. It shows data-dependent modulation of the DAC output via whatever mechanisms.
Last edited: