Cleaning up the cm106 audio card DAC output
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)
Here are the steps:
Download and decompress SimpleHIDWrite3.zip
To turn off interpolation and the s/pdif output,
select the USB audio device "USB Audio" VID 0D8C PID 0006 (Rev 0010 in my case)
enter report ID 00, data 20 02 30 01 (write 0x3002 to register 1) click 'set report' on XP or 'Write' on win2k.
to read back to make sure:
report ID 00, data 30 00 00 01 (read 00 00 register 1) click 'set report' on XP or 'Write' on win2k.
up should pop up "RD 00 30 02 30" indicating (last 2 bytes) that the register is 0x3002
This method is very *manual* and I plan to code it automatically into EzAudDac in the future.
Vector Scope photos made possible by a generous donation from Steve AKA mixedgas. The vectorscope really makes the difference clear. The image from the galvos doesn't reveal much difference.
Before:
After:
To reiterate, I really didn't see much difference in the scanned output before and after, both look great. This tweak won't help your horribly distorted output caused by improper tuning, bad connections, or neglected ground. But it does make things look nicer on the vectorscope
Enjoy!
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Originally Posted by Xer0
