I want to control the bass of song played by user from iPod music library.
I've searched on Google and got some AudioMixer samples which were of no help, but now I have got bass library i.e. libbass.a from http://www.un4seen.com/ which I think is quite useful.
But I don't know how I should adjust the bass of the song using slider.
Recently I got one more sample regarding this. But here the issue in this sample is I'm getting all equalizer's types like Dance, Pop, Rock, Bass, Jazz, Acoustic, Classical etc preset/predefined in an array given by AudioUnit Framework. But I want implement only bass in an slider. And you would must know that to implement any thing in slider we need values. But here in my case i'm not getting any value for anyone of those equalizer's preset types.
If you want to really bring out the bass on tracks played in the iPod, set your values to boost frequencies around 60-80 Hz, while cutting out some mids around 100-400 Hz. Dont forget to slightly increase highs as well, say around 2800 + Hz. I'm not familiar with how the software is set up, but from a studio artist's experience, the above mentioned frequency adjustments will take out any muddy or muffled sounds and really open up the low end. To handle what your asking: set your slider between 60-100 Hz.
Best of luck!
来源：https://stackoverflow.com/questions/11824207/how-can-we-control-bass-of-music-in-iphone-sdk