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I am building an iOS app that allows the user to play guitar sounds - e.g. plucking or strumming.

I'd like to allow the user to apply pitch shifting or wah-wah (compression) on the guitar sound being played.

Currently, I am using audio samples of the guitar sound.

I've done some basic read-ups on DSP and audio synthesis, but I'm no expert in it. I saw libraries such as csound and stk, and it appears that the sounds they produced are synthesized (i.e. not played from audio samples). I am not sure how to apply them, or if I can use them to apply effects such as pitch shifting or wah-wah to audio samples.

Can someone point me in the right direction for this?

kev
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1 Answers1

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You can use open-source audio processing libraries. Essentially, you are getting audio samples in and you need to process them and send them as samples out. The processing can be done by these libraries, or you use one of your own. Here's one DSP-Library (Disclaimer: I wrote this). Look at the process(float,float) method for any of the classes to see how one does this.

Wah-wah and compression are 2 completely different effects. Wah-wah is a lowpass filter whose center frequency varies slowly, whereas compression is a method to equalize the volume. The above library has a Compressor class that you can check out.

The STK does have effects classes as well, not just synthesis classes (JCRev) is one for reverb but I would highly recommend staying away from it as they are really hard to compile and maintain.

If you haven't seen this already, check out Julius Smith's excellent, and comprehensive book Physical Audio Signal Processing

e7mac
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  • Thanks e7mac for the reply. Btw, do you have references to other dsp library that can do what I mention? (I'm checking out your library out now btw). Thanks. – kev Mar 26 '14 at 01:15
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    Try https://github.com/micknoise/Maximilian, or http://theamazingaudioengine.com/ or http://bartolsthoorn.github.io/NVDSP/. Definitely nothing is standard though - most people end up writing their own – e7mac Mar 26 '14 at 05:34