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Re: Sound volume control in Matlab

It is also worth noting that Vista (or at least some audio drivers in Vista) have an output AGC option, which you will probably want to disable through the control panel.

I found this out the hard way - I was demonstrating in a class how changes in dB level affects loudness and all my samples came out the same!

Mark Huckvale

Bob Masta wrote:
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
Best regards,

Bob Masta
Data AcQuisition And Real-Time Analysis
Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!

Mark Huckvale, Director MSc Speech and Hearing Science
Speech, Hearing and Phonetic Sciences, University College London