On Sat, 05 Dec 2020 15:43:56 +0100, Ben Bell wrote:

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Like I said in the initial email, it feels like some sort of clock drift problem, where we're managing very slowly to collect more samples than we're reading -- to the tune of about 1 extra every few cycles -- and nothing on the consumer side is ever managing to compensate for that. I'm not even sure how that sort of drift would be possible though. Seems surprising.

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At least you can try the latest patch set destined for 5.11, which should improve the cases for the implicit feedback.

Aha! This actually was the key piece of information I needed. I haven't tried 5.11 or the latest patch set yet, but googling "implicit feedback" and learning abobut it led me to conclude that the Wing needs an entry in the quirks list in set_sync_ep_implicit_fb_quirk to properly enable it:

--- sound/usb/pcm.c.orig 2020-11-22 23:36:08.000000000 +0000 +++ sound/usb/pcm.c 2020-12-05 08:40:21.639600074 +0000 @@ -340,6 +345,7 @@ ep = 0x81; ifnum = 3; goto add_sync_ep_from_ifnum;

•   case USB_ID(0x1397, 0x050b): /* Behringer Wing */
    case USB_ID(0x0763, 0x2080): /* M-Audio FastTrack Ultra */
    case USB_ID(0x0763, 0x2081):
  
  
  

A week's worth of debugging and learning yielded a one line patch ;)

That's a interesting piece of information :)

Could you give lsusb -v output of the device? With the latest patch set, the driver can set up the implicit feedback mode automatically in certain cases. I'm not sure whether Behringer device follows that pattern. If not, we'd need to add the quirk manually.

thanks,

Takashi