Re: convert kAudioSessionProperty_CurrentHardwareOutputVolume to dB value
Re: convert kAudioSessionProperty_CurrentHardwareOutputVolume to dB value
- Subject: Re: convert kAudioSessionProperty_CurrentHardwareOutputVolume to dB value
- From: Kevin Dixon <email@hidden>
- Date: Mon, 16 Jul 2012 17:59:06 -0700
I was using a cosine, but even the amplitude was way too low
-Kevin
On Mon, Jul 16, 2012 at 5:35 PM, Roman Thilenius <email@hidden> wrote:
>
>
> do you use a FS cosine or a FS sqare?
>
> a cosine is not exactly the optimal material to measure power. :)
>
>
>
> On Jul 17, 2012, at 2:08 AM, 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
>>
>> Can anyone clarify this situation? It is imperative that I know the
>> actual attenuation so my algorithm can react correctly.
>>
>> Thanks in advance
>>
>> -Kevin
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