Re: Sound volume control in Matlab (Mark Huckvale )

Subject: Re: Sound volume control in Matlab
From:    Mark Huckvale  <m.huckvale@xxxxxxxx>
Date:    Wed, 13 Aug 2008 14:34:26 +0100

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 > purposes. > > Best regards, > > > Bob Masta > > D A Q A R T A > 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

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