Cleaning up the cm106 audio card DAC output

[dnar]

Cool, worked a treat, thanks man.

[Stoney3K]

A little known fact of the inexpensive cm106-based bluebox USB audio cards that some of us use as experimental DACs is that they implement a 'feature' called output sample rate doubling. This feature, on by default, effectively doubles the sample rate output of the card from 48kHz to 96kHz and because it doesn't accept data at 96k, it interpolates the data every other sample to create an artificial 96k output rate. This interpolation could be seen as beneficial, but it's not normally what a laser DAC is supposed to do. In their wisdom, the folks at CMedia allowed a way to turn it off via a driver interface control (that doesn't appear in the control panel)

This sounds like a 'software anti-aliasing filter' feature to save up on expensive components like a steep roll-off filter in the analog section of the DAC.

To be clear: Is the vectorscope image the output directly at the DAC output pin, or is it taken after the analog anti-aliasing filter on the card? I would be interested to see what the direct DAC output is.