How to get decibels accurately with AVAudioRecorder? - ios

Question

After comparing more than 20 apps, I found that the decibel values measured by each app are different.
// Method 1:
float power = [self.audioRecorder averagePowerForChannel:0];
float powerMax = [self.audioRecorder peakPowerForChannel:0];
power = power + 160 - 50;
int dB = 0;
if (power < 0.f) {
dB = 0;
} else if (power < 40.f) {
dB = (int)(power * 0.875);
} else if (power < 100.f) {
dB = (int)(power - 15);
} else if (power < 110.f) {
dB = (int)(power * 2.5 - 165);
} else {
dB = 110;
}
NSLog(#"power = %f, powerMax = %f , dB = %d",power, powerMax,dB);
// Method 2:
float level; // The linear 0.0 .. 1.0 value we need.
float minDecibels = -80.0f; // Or use -60dB, which I measured in a silent room.
float decibels = [self.audioRecorder averagePowerForChannel:0];
if (decibels < minDecibels)
{
level = 0.0f;
}
else if (decibels >= 0.0f)
{
level = 1.0f;
}
else
{
float root = 2.0f;
float minAmp = powf(10.0f, 0.05f * minDecibels);
float inverseAmpRange = 1.0f / (1.0f - minAmp);
float amp = powf(10.0f, 0.05f * decibels);
float adjAmp = (amp - minAmp) * inverseAmpRange;
level = powf(adjAmp, 1.0f / root);
}
NSLog(#"leval %f", level * 120);
There is a big gap between Method 1 and Method 2
So,Are these methods accurate? Is there a more correct way?