Control volume of one channel in objective-c - ios

Question

I have an really simple audio player with AVAudioPlayer with (at this point) one song.
It is simple to control the volume of both channels (left and right) at the same time.
But is it possible to control only the left channel or only the right channel?
In this way I can set the left speaker a little louder then the right or vice versa.

Answer 1

The AVAudioPlayer reference should be consulted to answer this question.
You can see from the interface that you can't control the left/right channel directly, but you can set the pan from -1 (full left) to 1 (full right). Perhaps this will achieve what you are looking for?
Using core audio will be much more difficult, but it should be able to handle this. Another possibility using AVAudioPlayer is to split the sound into its separate channels and to play them separately. Then, you can set the volume separately. There is an example in the documentation of how to ensure that two sounds play at exactly the same time. (And, you'll want to set the pan for each sound separately so that each sound plays correctly.)
A less efficient method is two play two copies of the .mp3 at once. (Caveat: I haven't tested this code.)
// assumes you have url for the file you want to play
AVAudioPlayer *first = [[AVAudioPlayer alloc] initWithContentsOfURL:myUrl error:nil];
AVAudioPlayer *second = [[AVAudioPlayer alloc] initWithContentsOfURL:myUrl error:nil];
first.pan = -1; // only play on left channel
second.pan = 1; // only play on right channel
first.volume = 0.6;
second.volume = 1.0;
NSTimeInterval shortStartDelay = 0.01;
NSTimeInterval now = player.deviceCurrentTime;
[first playAtTime: now + shortStartDelay];
[second playAtTime: now + shortStartDelay];