USB Mic Volume in 10.2.8
USB Mic Volume in 10.2.8
- Subject: USB Mic Volume in 10.2.8
- From: Doug Zwick <email@hidden>
- Date: Tue, 22 May 2007 12:11:34 -0600
I have some code that records audio data from a mic using Core Audio
(it is part of an internet conferencing application). It includes a
volume control, attached to a "recording level" slider in the
application's GUI. I am using AudioDeviceSetProperty on
kAudioDevicePropertyVolumeScalar to set the volume level it is
recording at. This works fine for every mic we've been able to find
under OS X 10.3.9 and 10.4.9. Unfortunately, under 10.2.8 some
devices return kAudioHardwareUnknownPropertyError. In looking through
the archives of this list, it seems to be a FAQ why this doesn't work
for every device, and the answer is because the device does not have
a volume control. I ran Audio MIDI Setup and verified that the
devices in question (all are USB headsets) do not show a volume
control under 10.2.8, but do show one under 10.3.9. I am curious
about the difference in behaviour between 10.2.8 and 10.3.9/10.4.8 --
was Core Audio enhanced to simulate a master volume control for such
devices? Is my only option for adjusting the volume of the audio data
in this situation to track the volume level myself, and multiply each
sample by some fraction (e.g. by 0.7)? I know that the desired
multiplier value is not in a linear relationship with the volume
slider position, so I shouldn't just multiply by the
kAudioDevicePropertyVolumeScalar property value -- what is a good
function to obtain a multiplier from the scalar value (e.g. sqrt(v),
log(v), etc.)?
Or is there a better way of implementing a "recording level" control?
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