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Re: Changing the way the OS responds to a USB DAC
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Re: Changing the way the OS responds to a USB DAC


  • Subject: Re: Changing the way the OS responds to a USB DAC
  • From: Brian Willoughby <email@hidden>
  • Date: Fri, 02 Mar 2012 17:18:44 -0800

You are barking up the wrong tree. If you want the volume to be "disabled" then you need to insure - as the user and operator - that the volume is set to 0 dB.

CoreAudio treats each audio device according to the controls advertised by that device. If a USB Audio device does not have volume, then volume will not be enabled. It's not that the volume is there and disabled, it's that there is no software-controlled volume on that hardware. The reason that the optical digital outputs have volume controls is because Apple's built-in driver provides a volume control to CoreAudio. The reason that your Beresford and Fiio do not have volume control is because of the USB Audio Descriptors. The USB Audio Class Specification defines a standard way for each Device to communicate its capabilities.

If you want to alter the hardware and software abilities of a specific device that you are not manufacturing yourself, then you're really asking for trouble. The CoreAudio mailing list and the USB mailing list are Apple's avenues for supporting third party hardware and software developers who are creating their own products. I get the impression that you are a user who desires existing products to behave differently than intended by their respective manufacturer, so you're getting into the realm of hacking. I don't think that Apple has a support line for hackers. :-)

You could file a suggestion with Apple that they add a feature to their built-in optical digital audio output that would force the volume to unity gain (0 dB). That would be compatible with a more audiophile expectation, although it might be contrary to the general expectations of a non-audiophile user. Apple is in control of whether their built-in optical output presents a volume control, so use the feature suggestion facilities to communicate your desire to Apple.

Brian Willoughby
Sound Consulting


On Mar 2, 2012, at 13:14, SB Tech wrote:
I've received no responses to this. I'd appreciate being told whether I'm barking up the wrong tree or people here just don't know anything. If I haven't heard anything by Monday I'll remove myself from the list.


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