Hi,
What is the difference between peakPowerForChannel and averagePowerForChannel methods of AVAudioRecorder?
And why is the value returned is negative? Isn't it supposed to be 0 for no sound and go up when the amplitude of sound rises? How can I convert to a more "readable" format?
Thanks.
While I've not looked at those values, since it's related to audio volume, I'd guess that it's measured as a change in decibels.
0 would be maximum loudness and anything quieter than that could be expressed as a drop in decibels.
Positive and negative don't matter. Just remember that it's a logarithmic scale where you're measuring the difference in loudness (or perceived loudness).
Peak power means taking the maximum value of all the absolute values of all the samples. It's useful for preventing clipping of the audio.
Average power is the RMS (root-mean-square) of the samples. This is useful to determine how loud the audio sounds to human ears.
The value is negative because it is expressed in decibels, where 0 dB is equal to the maximum value of the audio system. It's a log10 scale, and the formula for conversion is:
db = 10 * log10 (level);
where db is decibels and level is the scalar value ranging from 0.0 to 1.0. So when the level is 0.0 (silent), the result is negative infinity.
If you want a "readable" format, you can use a level meter (UIProgressView or your own) where the max is 0.0 and the min is -60.0 (you can adjust depending on the noise floor). Once you're used to decibels, they make more sense than linear levels.