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ALSA: usb-audio: relax urb data align. restriction HVR-950Q and HVR-850 only

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Addressing audio quality problem.

In sound/usb/usbaudio.c, for the Hauppage HVR-950Q and HVR-850 only, change
retire_capture_urb to allow transfers on audio sub-slot boundaries rather
than audio slots boundaries.

With these devices the left and right channel samples can be split between
two different urbs. Throwing away extra channel samples causes a sound
quality problem for stereo streams as the left and right channels are
swapped repeatedly, perhaps many times per second.

Urbs unaligned on sub-slot boundaries are still truncated to the next
lowest stride (audio slot) to retain synchronization on samples even
though left/right channel synchronization may be lost in this case.

Detect the quirk using a case statement in snd_usb_audio_probe.

BugLink: https://bugs.launchpad.net/ubuntu/+bug/495745

Signed-off-by: John S. Gruber <JohnSGruber@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
John S. Gruber
2009-12-27 12:19:58 -05:00
committed by Takashi Iwai
parent adc8d31326
commit 98e89f606c
2 changed files with 30 additions and 2 deletions
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sound/usb/usbaudio.h
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@@ -125,6 +125,7 @@ struct snd_usb_audio {
struct snd_card *card;
u32 usb_id;
int shutdown;
unsigned int txfr_quirk:1; /* Subframe boundaries on transfers */
int num_interfaces;
int num_suspended_intf;