Background:
It was found that a considerable level difference existed when a user replaced a DMK URIx with a new URIxB. This is a result of the C-Media CM119B chip requiring a different driver formula as compared to the CM108, CM119, and CM119A. Whenever a CM119A URI is replaced with a CM119B URI, the symptiom is very low audio levels both in the TX and RX processing. Using stock ASL1.01 or HamVoIP 1.5, and a URIxB, there is a 40 dB input to output reduction in level as compared to a standard URIx. Some of this loss exists in the TX path while some of it exists in the RX path.

I first built a Raspberry Pi model 3B (not plus) using ASL-1.01. I did all of the recommended updates, and used this box along with a standard URIx to do the baseline testing. Testing was made by using a modified SYBA fob as a audio test interface with my laptop running a program called TrueRTA. TrueRTA is a real time audio analyzer program available in several levels. I have the 24db/octave version. This software allows for sweep response testing over all octaves of the audible sound range. The testing was done betewen 20Hz and 20 kHz for this application. A graph of the test device (by itself) is available to show basic response of just the test set, at a level of 0 dB.

Graphs of both simpleusb and usbradio were produced using stock ASL1.01 and the standard, original URIx. Then, subsequent tests were done prior to and after the code was modified to adjust for the differences between the URIx, and UrixB. These graphs show that after the code was modified, a small differential still exists, but is well within the tuning range of most set-ups.