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: Robert Penland <email@hidden>
- Date: Tue, 13 May 2003 10:23:39 -0700
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,kIOAudioCon
>
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,kIOAudioCon
>
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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