I'm wondering if there is a way to select part of a sample at a given frequency. The only way I can think to index the sample by frequency is using an FFT, but doing that seems to mess up the sample so that it's not actually playable anymore. I was wondering how else one might select the part of a sample at a given frequency whilst keeping the sound intelligible? 

Edit: The exact instructions were "synthesize an example of each vowel of pitch 150 Hz and duration 5 seconds".

Edit: I completely misunderstood what I needed to do originally. New question is here: [Synthesizing vowel from existing audio sample jin matlab](https://stackoverflow.com/questions/19910606/synthesizing-vowel-from-existing-audio-sample-jin-matlab)