[alsa-devel] Resend: Incorrect sbits for snd-usb-audio

Takashi Iwai tiwai at suse.de
Sun Dec 8 10:20:57 CET 2013

At Fri, 6 Dec 2013 14:57:46 -0600,
Sander Jansen wrote:
> Hi,
> I had send this out earlier back in September, but never got a response.
> I have a Focusrite Scarlett 2i4 USB Audio Interface. The audio format
> exposed by ALSA for  this device is S32_LE. From the hardware specs and
> lsusb. it supposed to only have a 24 bit resolution (with the LSB bits set
> to 0):
> AudioStreaming Interface Descriptor:
>         bLength                 6
>         bDescriptorType        36
>         bDescriptorSubtype      2 (FORMAT_TYPE)
>         bFormatType             1 (FORMAT_TYPE_I)
>         bSubslotSize            4
>         bBitResolution         24
> When I query the sbits for this device, I expect it to return 24, but
> instead it returns 32. Looking through the usb audio driver code, it
> doesn't look like this information is actually exposed to userspace. The
> 'parse_audio_format_i_type'  in usb/format.c merely returns the supported
> formats, but doesn't include any msbits info. (and it doesn't look like it
> can be easily changed to return the msbits info as well).
> Was this intentionally left out, or is this a missing feature in the driver?

It's just because of laziness because almost no applications check the
msbit but only the format type.  Feel free to send an enhancement



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