[wdmaudiodev] Re: Are volume and mute controls optional for UAC 1.0 device?

  • From: "Robert S. Giaraffa" <Robert.Giaraffa@xxxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Thu, 4 Dec 2014 22:18:35 +0000

My USB audio 1.0 class-compliant device has configurable mute and volume 
control support, specified in the bmaControls bytes of a feature unit.  The 
device works as expected under these conditions:

    Master Mute enabled, Left/Right Channel volumes enabled
    Master Mute disabled, Left/Right Channel volumes enabled
    Master Mute enabled, Left/Right Channel volumes disabled

However, when both the mute and channel volume controls are disabled in the 
feature unit descriptor, the device installs correctly but does not appear as a 
playback device in the Sound dialog box.  The USB traffic appears normal except 
that the host does not send out an initial  20ms burst of zero-value samples, 
as it does when playback is working.

When I remove the playback feature unit descriptor from the Config descriptor 
and adjust the topology accordingly, the playback works as expected (i.e. 
Windows scales the samples according to volume, and samples are 0 when muted).

I should note that this behavior was observed on Win7 64-bit, and that the 
device's HID descriptor always specified consumer control volume/mute controls 
even if they were disabled in the feature unit descriptor.

Is it expected that a playback device cannot have a feature unit with both mute 
and volume disabled?



-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx 
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Matthew van Eerde
Sent: Wednesday, December 03, 2014 11:52 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: Are volume and mute controls optional for UAC 1.0 
device?

Some render devices support compressed formats (e.g., S/PDIF-ized Dolby 
Digital). If an app is playing to the device using a compressed format, Windows 
will not be able to perform software volume or software mute.

So, Windows recommends having at least a hardware mute on devices that support 
compressed formats.

-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx 
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Clemens Ladisch
Sent: Tuesday, December 2, 2014 11:51 PM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: Are volume and mute controls optional for UAC 1.0 
device?

Robert S. Giaraffa wrote:
> Are Mute and Volume controls both optional for a USB Audio Class 1.0 
> compliant device?

Yes.  There is hardware that does not have these controls (e.g., the Edirol 
UA-1A).

> Will Windows perform the volume/mute functions if the device does not 
> declare these controls?

Yes.


Regards,
Clemens
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