Re: convert kAudioSessionProperty_CurrentHardwareOutputVolume to dB value
Re: convert kAudioSessionProperty_CurrentHardwareOutputVolume to dB value
- Subject: Re: convert kAudioSessionProperty_CurrentHardwareOutputVolume to dB value
- From: Brian Willoughby <email@hidden>
- Date: Tue, 17 Jul 2012 10:53:58 -0700
On Jul 16, 2012, at 17:08, Kevin Dixon wrote:
So it seems that kAudioSessionProperty_CurrentHardwareOutputVolume
returns arbitrary volume units instead of linear gain.
For example when i get the value 0.711712, I convert to dB with
20.0f * log10(volume)
returning ~ -2.95 dB.
However when I measure a 0dB FS tone from my headphone output, with
the volume at 0.711712, the observed power is more in the neighborhood
of -16dB
-16 dB what?
Decibels are relative, therefore, citing a -16 dB measurement is
incredibly vague when there is no reference value. Is that -16 dBm?
-16dBV? -16 dBmV?
With the volume at 1.000000 (0 dB), what power do you expect to measure?
Also, don't forget that there are potentially other volume settings
in the path, and they must all be 0 dB if you want to measure one of
them accurately.
Brian Willoughby
Sound Consulting
Can anyone clarify this situation? It is imperative that I know the
actual attenuation so my algorithm can react correctly.
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