USB Sound cards detected as "microphone" instead of "line in" decrease the decoding quality in digital modes


A lot of HAMs love to use external USB Sound Cards that are embedded in digimode interfaces.

Just to name a few:

What is the problem?

USB sound cards with chipset TI PCM2900 series PCM2904 and below in combination with Windows Vista and later show up as microphone instead of line in.
As a consequence, windows adds 30 db to 50 db of gain and clips the signal.
Many HAMs have workarounded this issue by turning the output of the interface and the level in windows all the way down.
This reduces the dynamic range and puts the signals into the noise floor.

How to check if my sound card interface is affected?

Go to Windows Control Panel -> Hardware and Sound -> Sound
Go to the "Recoding" tab, select your device and click "Properties".
Go to "Levels", right click to the slider and select "decibels".
If 100% on the slider reads +30db, you are affected by the bug.
If the device was properly enumerated as a line in device, 100% on the slider would be 0db.


The solution is to lower the slider to 0 db.
On my computer, -0.4 db has been the closed value I could get and it was fine.
Increase the output of your interface and see the difference.