Question

I want to make a simple audio equalizer for the iPhone, but I don’t know how to start. The equalizer should be really simple and just change bass, high, distortion and maybe echo and chorus.
How can I start? Maybe a sample code would be helpful.

Answer 1

Firstly you’re getting confused in your terminology.

An equalizer just changes the frequency response of an audio channel. It usually has a fixed number of frequency bands, whose individual gains can be controlled by the user.

Distortion, echo, chorus, etc are effects – in the digital domain they are simply algorithms that are applied to an audio channel to modify the data passing through it.

So you need to decide what it is that you are designing: an equalizer, some kind of effects processing gizmo, or maybe some combination of these.

Once you have a rough design for what you want to implement, then you can start work on the various algorithms that are going to be used to implement this design. For the equalizer you can consider either doing frequency domain filtering or implement a time domain filter bank. For the effects part you will need to do some research into the various different effects and how they are implemented, e.g. distortion usually uses some non-linear transfer function to introduce additional harmonic content.