Question about usb_device_composite_hid_audio_unified_lite application... Linux vs W10

[EdSutter]

I am working on custom hardware (core system is based on MIMXRT1060-EVK) that runs code derived from the usb_device_composite_hid_audio_unified_lite application in the SDK.   My system is a multi-channel (6-in/8-out) audio card, but the current configuration is just 1-in/1-out.  I hook my board up to a Linux machine and test the audio features using aplay/arecord and things are fine.  I've also set my device up as the default audio device on Linux and connect to youtube and the audio output (through my board's speaker) is fine.  So far, so good... 

Yesterday I hooked my system up to a W10 PC and I found that the audio output (to my speaker) is playing but it is distorted quite a bit.  Can't really describe the distortion, I can hear the audio well enough to know that it is streaming but with a lot of what sounds like saturation (clipping) and even frequency change.  It almost seems like W10 is forcing down two channels, but I'm only digesting one.  

Anyone have a clue why it would be perfect on Linux but distorted on Windows-10?

[Alexis_A · Accepted solution]

Hello @EdSutter,

As the readme of this example mention this is a known issue:

I will suggest enabling the define USB_DEVICE_WORKAROUND_AUDIO_20_WINDOWS in the usb_device_descriptor.h and try again.

Best Regards,

Alexis Andalon

[EdSutter]

Hi Alexis,

I've updated my application to SDK 2.8.6, and that alone (leaving USB_DEVICE_WORKAROUND_AUDIO_20_WINDOWS at 0) did the trick.  I will compare both configurations (set and unset) to see if there is any noticeable difference.

Now I need to get a better understanding on how this feedback endpoint works.  If you can recommend any documentation on this, that would be great.

Thanks,

Ed

[Alexis_A]

Hello @EdSutter,

There is not much documentation about this but you could try looking at the following USB Specification 1.0, section 5.10.4.

Also, this post address the same problem.

Best Regards,
Alexis Andalon

[EdSutter]

Hi @Alexis_A,

I have been assuming that the SDK implements this feedback endpoint.  I see snippets in the code that mention it.  Is it tested and known to be working?

Ed

[EdSutter]

Hi Alexis,

I'll give this a try, but first I have to update my code to the latest SDK...

I have been running with 2.7.0, so its time...

Will post the results when I complete that transition.

Thanks,