Re: Sound volume control in Matlab

[Bob Masta <audio@xxxxxxxxxxx>]

On 11 Aug 2008 at 18:18, Stuart Rosen wrote:

> Has anyone tried to control sound volumes in Vista
> through Matlab? There are extra complications over XP in
> that each application window seems to have its  own
> volume setting (which is a good thing) but that seems to
> be limited to an overarching volume control that applies
> to all windows. 

Be very careful with volume controls in XP or Vista.  
Windows uses the "kernel mixer" to manipulate the digital 
stream so multiple applications can use the same device. It
basically intercepts the data and scales it down before 
sending it to the D/A.  The D/A thus gets the sum of all 
the active streams.  The danger is that this is all done 
"behind your back"... an individual application does not 
know that its volume range has been shortened, or by how 
much.  

In principle you could just make sure that all other apps 
are fully closed before you start your desired app, but 
sometimes it's not clear if an app is really gone or just 
lurking in the background (and eating up volume range).

One way to avoid this is to get a separate sound card that
is used *only* for your experimental setup.

My understanding is that software that uses ASIO drivers 
avoids the problem, by bypassing the kernel mixer.  I have
also heard that "kernel streaming" can be used for similar
purposes.  

Best regards,


Bob Masta
 
            D A Q A R T A
Data AcQuisition And Real-Time Analysis
           www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
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