ALSA: usb-audio: Add implicit feedback quirk for Zoom UAC-2
The Zoom UAC-2 USB audio interface provides an async playback endpoint ("1 OUT (ASYNC)") and capture endpoint ("2 IN (ASYNC)"), both with 2-channel S32_LE in 44.1, 48, 88.2, 96, 176.4, or 192 kilosamples/s. The device provides explicit feedback to adjust the host's playback rate, but the feedback appears unstable and biased relative to the device's capture rate. "alsaloop -t 1000" experiences playback underruns and tries to resample the captured audio to match the varying playback rate. Forcing the kernel to use implicit feedback appears to produce more stable results. This causes the host to transmit one playback sample for each capture sample received. (Zoom North America has been notified of this change.) Signed-off-by: Keith Winstein <keithw@cs.stanford.edu> Tested-by: Keith Winstein <keithw@cs.stanford.edu> Cc: <stable@vger.kernel.org> BugLink: https://lore.kernel.org/r/20201027071841.GA164525@trolley.csail.mit.eduSigned-off-by: Takashi Iwai <tiwai@suse.de>
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