[wdmaudiodev] Re: Peak Meter in Core Audio APIs

  • From: Clemens Ladisch <clemens@xxxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Mon, 21 Jun 2010 09:50:17 +0200

Andrew Mindrin wrote:
> Tim Roberts wrote:

No, he quoted that.

> >   3. current volume (in dB) + 20 * log10( peak value )
> 
> I agree with your formula for PPM meter, but it doesn't correspond to 
> low-range of
> IAudioEndpointVolume::GetVolumeRange.

Can you give an example where it doesn't correspond?

> 1. Current Volume (in dB) * Peak Value

So if the current volume is -12 dB, and the peak value is at 0.5,
the meter would show -6 dB?

> This is VU meter formula.
> 
> 2. 20 * log10( peak value )
> 
> This is PPM meter formula.

The difference between VU meters and PPM meters is in the rise and fall
times, not in the mapping of input values to the display.

> It has no correlation to the range of volume levels returned by
> IAudioEndpointVolume::GetVolumeRange.

Yes, because the current volume doesn't appear in this formula; it
implicitly assumes that peak = 1.0 is at 0 dB.


Regards,
Clemens
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