How to boost frequency range of MPMediaItem? (Like parametric EQ, e.g., boost 500 Hz by 12 dB)

Question

I'm looking to build a really simple EQ that plays a filtered version of a song in the user's library. It would essentially be a parametric EQ: I'd specify the bandwidth, cut/boost (in dB), and centre frequency, and then be returned some object that I could play just like my original MPMediaItem.

For MPMediaItems, I've generally used AVAudioPlayer in the past with great success. For audio generation, I've used AudioUnits. In MATLAB, I'd probably just create custom filters to do this. I'm at a bit of a loss for how to approach this in iOS! Any pointers would be terrific. Thanks for reading

Answer 1

iOS ships with a fairly sizeable number of audio units. One of kAudioUnitSubType_ParametricEQ, kAudioUnitSubType_NBandEQ or kAudioUnitSubType_BandPassFilter is probably what you want depending on whether you want to control Q as well as Fc and Gain.

I suspect you will have to forego using higher-level components such as AVAudioPlayer to make use of it.

The relevant iOS audio unit reference can be found here