I started using the SoundManager class created by Nick Lockwood. It seems like it's well supported in the iOS community and I'm trying to figure out ways of getting better performance playing back sound effects.
I've also created my own class to make sure sounds aren't playing to close in time to each other, and keep track of polyphony, but even using SoundManager's methods by themselves, I'm getting poorer performance than I hoped for.
I have SoundManager added to my delegate as instructed. I expect that even though aif/wav format would be larger file size, I would get better performance with these formats other than something that would need to decompress. I also tried these formats in the caf (Core Audio Format) container.
I'm doing this anytime I want to play with sound.
[[SoundManager sharedManager] playSound:@"bulletShot.aif"];
Also, when my scene is initialized, I tried doing this to hopefully preload it:
[[SoundManager sharedManager] prepareToPlayWithSound:@"bulletShot.aif"];
The sound is really short, maybe less than a quarter of a second, but still the frame rate drops about 10 frames for about 100-200 ms every time the sound is played. The sound's sample rate is 32 kHz and the bit rate is 16 and mono.