Re: System Mute Problem
Re: System Mute Problem
- Subject: Re: System Mute Problem
- From: Brian Willoughby <email@hidden>
- Date: Mon, 9 Feb 2009 12:38:46 -0800
I'm just guessing here, since I have so few details: Could it be a
discrepancy between 'bus' and 'channel' that is causing this?
Typically, CoreAudio deals with audio devices in terms of busses which
each have a number of channels. While a few rare audio interfaces
have each channel on its own bus (which is very annoying for the low-
level programmer), it's typical to place Left and Right on a single
bus. As I said, I'm guessing, but it could be that OSX thinks it's
setting a bus volume which includes both channels with one value, but
on your device it's only affecting Left and not Right.
This could easily be a USB-Audio issue. In my experience, Apple is
100% in compliance with the USB specifications. If you have trouble
with a USB device only on OSX, then it is very likely that your USB
descriptors are wrong. The fact that it works on Windows means
nothing, because that OS is notoriously bad at the finer details of
standards. I suggest that you pore over the USB-Audio specification
and make sure you have everything just right in your descriptors. I
assume that you do not have a custom audio driver for your device on
OSX, but if you do, then that would be an obvious suspect as well.
Brian Willoughby
Sound Consulting
On Feb 9, 2009, at 11:24, Gordon Rankin wrote:
I am not sure if this is core audio or USB...
Anyways, I designed a USB Digital to Analog converter which has system
wide volume for Left and Right as well as system mute. As seen in the
enumeration below:
Audio Class Specific Feature Unit ID: 7
Source ID: 5
Control Size: 2
Number of Channels (ch): 2
Master Channel:......................... ( Mute )
Left Front:............................. ( Volume )
Right Front:............................ ( Volume )
Feature Unit Name String Index: 0
~~~~~~
The volume works fine but in the System Preference if you check the
Mute box only the Left channel is effected as whatever controls this
action is taking a snapshot of the present volume and then setting it
to zero to mute it. But is only doing this to the left channel.
In other words the mute is not being acted on at all but merely the
volume is used as the mute and it is broken because it is only doing
the left channel and not the right channel.
All other operations are working fine. Volume, Balance etc... all work
fine.
This works fine in all other operating systems.
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