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46

answers:

2

Hi,

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

A: 

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.

hotpaw2
Thanks! Looks complicated but it sounds like the right direction to follow. André.
André
A: 

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.

Nik Reiman
This is indeed what I do. Would you have any example of a simple EQ code to point me to by any chance ? Thanks.
André
The best resource for sample DSP code is musicdsp.org. Here you can find a sample 3-band EQ: http://musicdsp.org/archive.php?classid=3#236 Don't forget to mark an answer as correct if you find it helps solve your problem. ;)
Nik Reiman