Re: linear vs. log Hz
Re: linear vs. log Hz
- Subject: Re: linear vs. log Hz
- From: Bill Stewart <email@hidden>
- Date: Tue, 15 Oct 2002 18:56:34 -0700
You can also look through that code itself as the generic view is in the SDK
and the use of the calls Chris mentions can be found there.
Bill
on 15/10/02 4:18 PM, Chris Rogers wrote:
>
I think there's a difference between the "generic view" in Logic compared
>
with the Apple supplied Generic View. If you try out your AudioUnit
>
in AudioUnitHosting, I think you should see the Hz parameter displayed
>
with units of Hz, but on a log scale. Logic may not do the proper conversion
>
to display this on a log scale...
>
>
So, hosting apps - it's often a good idea to display parameters published
>
with units of Hertz on a log scale!
>
>
Chris
>
>
>
>
> Chris,
>
>
>
> I'm not sure I was clear enough. Maybe I should elaborate more:
>
>
>
> ok let's say I declare my frequency parameter as:
>
>
>
> { "Filter Frequency" , 0 , kAudioUnitParameterUnit_Hertz
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> , 50.0f ,
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> 8000.0f , 1000.0f , 0 },
>
>
>
> in my AudioUnitParameterInfo...now I launch logic, open the AU and the
>
> generic view creates sliders for my parameters...the frequency slider
>
> looks good, it's says it's unit is in Hz etc...but if I move the slider
>
> at 50% i get a frequency around 4200 Hz which is good if I want that
>
> parameter to be scaled linearly...
>
>
>
> if now I declare is as a generic value ranging from 0.0f to 1.0f, I can
>
> do something like that:
>
>
>
> myScaledFreq=pow(10.0f,3.90f*fFreq)+49.0f
>
>
>
> this curve fits my particular needs, but then logic displays only 0.0
>
> to 1.0 values for that parameter which is normal since i haven't
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> declared it as a kAudioUnitParameterUnit_Hertz this time. So my
>
> question was: how can I declare my parameter like in the second case
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> and be able to tell the generic view to display my scaled frequency.
>
>
>
> Sorry to bother you again with that...
>
>
>
> Franck
>
>
>
>
>
>> Franck,
>
>>
>
>> Please notice that the generic view will notice that a parameter's
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>> units
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>> are Hertz and then do the reasonable exponential curve scaling for the
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>> slider control. We provide functions AUParameterValueFromLinear()
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>> and AUParameterValueToLinear() in AudioUnitUtilities.h to convert back
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>> and forth in a general way between log <-> linear.
>
>>
>
>> We also have the units type kAudioUnitParameterUnit_AbsoluteCents
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>> which publishes a parameter explicitly with a log frequency scale.
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>> kAudioUnitParameterUnit_AbsoluteCents has the interesting property of
>
>> corresponding to the pitch of 100 times a MIDI note number!
>
>>
>
>> Chris Rogers
>
>> Core Audio
>
>> Apple Computer
>
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