Peak and averagePowerForChannel are nice, but what about the actual power?

Question

Am I missing something, or is there no direct way in AVAudioPlayer to get the actual power of an AVAudioPlayer object sample? There's clearly some way to get it, since the various metering apps (a la avTouch) show a meter with actual power levels along with (usually) the average power levels. So how do I access the current level when the only properties available are for peak and average?

Thanks.