Question

Do any of the iPhone Audio frameworks (or open source frameworks) support scrubbing and 2x (i.e. ability to play audio at 2X, 3X the normal speed)?

Answer 1

If you mean you want to eliminate the chipmunk effect, you have two options.

1.I have done a personal research on this in January.

Fast Fourier Transforms on the mp3 byte stream

You could also find useful this documentation from the IEEE:

Real-Time Signal Estimation From Modified
Short-Time Fourier Transform Magnitude Spectra

2.There is a built framework that does this quite well. They have a paid version also. You can read more about this in my study above.

DSPDimention Official site

Here’s a transcript of the email exchange I had with the boys at TheDSPDimention.

• My request:

We’re looking to integrate your iPhone DIRAC module into our application. The goal is to time-stretch the running mp3 file without decreasing or increasing the pitch. We want to perform this task in real time on the iphone. Is your product capable of doing this task? If so, please reply to the specified email address as soon as possible.

• The answer

Thank you for your interest in our products. DIRAC’s primary goal is to provide high quality results for both musically monophonic and polyphonic sources. While the low-quality preview mode of DIRAC2 is aggressively optimized and runs in a near-
realtime context on the 3GS hardware I doubt that there is enough headroom to do MP3 decoding at the same time. We would like to encourage you to experiment with our free LE version in your app to see if it suits your needs. You can get that from our
download page on http://www.dspdimension.com If there’s anything else we can help you with please don’t hesitate to ask.

If you’re not interested in real time mp3 stream manipulation.. then DIRAC_LE is just the thing you’re looking for.

Cheers