representing sound graphically as wave

Question

I Have created an app that records and plays sound and I am looking for a way of showing a simple wave representation of the recorded sound, no animation is necessary, just a simple graph.

It would also be nice it is was possible to select a subset of the wave and ofcourrse even more nice playing that section aswell.

To sum up, what I'm looking for:

1. A way of graphically represent a recorded sound as a wave (eg as seen in audacity)
2. A way of graphically selecting a subset of the wave representation.

And to clarify a bit further of what I'm looking for:

1. If there is a lib for this I'd be insanely happy :)
2. A hint on what components to best use for handling the graph drawing.
3. A tip on how to handle the selection within the graphical component.

Answer 1

I already did this in another application and have been struggling with it for a while ...

You would divide the number of samples the audio file has by the number of pixels you have to display the graph. This gives you a chunksize. For all the "buckets" you calculate the min and max value and display them in relation to the sample resolution used.

Can provide further examples if needed.

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Regarding the graphics stuff: (I am not an iOS developer but Mac programming isn't that much different I think.) Just create a subclass of NSView ( should be UIView in iOS ) and override the drawRect method. Then just create a function which you pass an array of values for your file and draw a bunch of lines to the screen. It's no black magic here!!

This is really nothing you would need a library for! And, as another positive aspect : if you keep it generic enough you can always reuse it.