Re: Slider values on an Input Volume(Gain) Control
Re: Slider values on an Input Volume(Gain) Control
- Subject: Re: Slider values on an Input Volume(Gain) Control
- From: Jeff Moore <email@hidden>
- Date: Tue, 13 May 2003 11:51:03 -0700
There isn't a way to defeat the curve, but I'll add that as a feature
request.
At any rate, I wouldn't lie about your volume values because tuning
them for one app, the System Prefs, will undoubtedly lead to unusual
results in other apps.
On Tuesday, May 13, 2003, at 10:23 AM, Robert Penland wrote:
Jeff,
Is there anyway to inhibit this behaviour or is the equation for the
"curve"
that you described published somewhere?
I am trying to get our 0dB point to be in the middle, but with the
curve
applied it isn't. Is it better just to lie to core audio on the dB
range so
that we get the mapping that we want and have the dB range incorrect?
(I
think the only thing that I've seen that actually displays the dB
range is
Daisy)
Thanks,
Rob
--__--__--
Message: 7
Date: Mon, 12 May 2003 17:24:57 -0700
Subject: Re: Slider values on an Input Volume(Gain) Control
From: Jeff Moore <email@hidden>
To: "'email@hidden'" <email@hidden>
The HAL applies the curve you observed to all IOAudioLevelControls
whose dB range is over 30dB.
On Monday, May 12, 2003, at 04:17 PM, Robert Penland wrote:
I'm having a little problem with the values that get sent to the gain
control of my AudioInput driver. If I create the control with the
following
line
myGainControl = IOAudioLevelControl::CreateVolumeControl(myCurrent,
myMin, myMax, 0,(18 <<16),
kIOAudioControlChannelIDAll,kIOAudioControlChannelNameAll,0,kIOAudioCo
n
trolU
sageInput);
I get a nice linear mapping from myMin to my Max when the gain control
slider in the audio preferences pane as the slider is moved from min
to max.
Since, my input hardware can also attenuate the input signal I thought
I
could modify the call as follows:
myGainControl = IOAudioLevelControl::CreateVolumeControl(myCurrent,
myMin, myMax, (-18 << 16),(18<<16),
kIOAudioControlChannelIDAll,kIOAudioControlChannelNameAll,0,kIOAudioCo
n
trolU
sageInput);
and still get a linear mapping from myMin to myMax, and whoever cared
in the
system would know that the input was also getting attenuated. If I do
this
however, the mapping of slider values from the audio preferences pane
gain
slider is no longer linear to my hardware. It almost looks like it is
some
sort of logrithmic relationship with the lower half more heavily
weighted
than the upper half. Can someone explain why this happens with a
negative
value for the min dB setting ?
Thanks,
Rob
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--
Jeff Moore
Core Audio
Apple
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