How to make a simple EQ AudioUnit (bass, mid, treble) with iOS?

Question

does anyone know how to make a simple EQ audio unit (3 bands - low, mid, hi) with iOS ? I know how to add an iPod EQ Audio Unit to my AU Graph. But it only give you access to presets and I need proper control of the EQ.

I've looked around for some tutorials or explanations but no luck.

Thanks.

André

Answer 1

The iPhone doesn't exactly support custom AudioUnits. Or, more precisely, it doesn't allow you to register an AudioUnit's identifier so you could load it in an AUGraph. You can, however, register a render callback, get raw PCM data, and process it accordingly. This is how I've implemented effect processing in the iPhone.

Answer 2

I would highly recommend you to use my NVDSP library, it allows easy audio DSP'ing, including the filters required to make an equalizer in iOS: https://github.com/bartolsthoorn/NVDSP

Answer 3

I've written two Blog-Entries about this issue and how to get equalization on iOS working. It uses the libsox library (cross compiled).

First post explains how you build libsox: http://uberblo.gs/2011/04/iosiphoneos-equalizer-with-libsox-making-it-a-framework

The second explains how to use it: http://uberblo.gs/2011/04/iosiphoneos-equalizer-with-libsox-doing-effects

please up the answer if it helped you! thanks!

Answer 4

you can implement using same classes as used in speak here sample code ,only to generate properties like peak powervalue and average powervalue you need to do calculation in callback function and it works.

Answer 5

This ancient Motorola AN2110 App Note explains how to write your own fully controllable 10-band equalizer (and 10 bands of real-time audio IIR filters will consume well under 10% of an iPod Touch's ARM CPU). Not sure about how to integrate this with an AU Graph, but this type of EQ can easily be integrated into PCM Audio Queue buffer callbacks.