Lexicon Alpha - Firmware Bug
I have two Lexicon Alpha units to drive two speaker setups. On one of these I also use for video conferencing with a headset. Occasionally the headset gets pulled out during a call and the mic defaults to the Alpha. The playback on the alpha gets messed up thereafter.
Until today I thought it was a specific issue to the conferencing app. However its not as I have just reproduced it on my other setup by just opening Windows 10 sound settings whilst using Spotify to listen to music.
With some further investigation I now know what the issue is.
Both Spotify and Windows sound settings use WASAPI Shared mode unlike some pro audio apps which will use exclusive mode so as to be able to control the sample rate directly/minimize latency. The default audio format chosen by based on the USB descriptor for playback is 24bit @ 48khz; however the default audio format chosen for record is 24bit @ 44.1khz.
This should be fine (although most modern headsets default to 48khz on both even if they support 44.1khz these days AFAIK) but this combination causes a bug.
If an app is already playing audio at 48khz and then another (or the same) starts recording audio at 44.1khz I believe the Lexicon starts processing the audio its receiving at 44.1khz but Windows is still supplying samples at 48khz hence some get dropped. This causes terrible clipping.
The work around is to explicitly set recording format in the advanced settings tab of the sound control panel for the device to 48khz @ 24bit.
This is NOT a driver issue as I am using the generic USB audio driver in Windows. The problem lies in the device or firmware.
Any chance of a fix?