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I'm using matlab and have a recorded sample of a vowel sound. I'm looking to make use of my existing sample to synthesize a vowel sound at a pitch of 150Hz (lasting 5 seconds). I originally thought that I'd just have to take a sample of my existing vowel sound at the given frequency but, obviously, that doesn't actually work.

So, now, I'm pretty stumped on how one would actually go about synthesizing the vowel sound?

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The General
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    So you have a sample of the vowel at a known pitch and just want to change the pitch? – Luis Mendo Nov 11 '13 at 16:01
  • @LuisMendo: Not really, I'm looking to create a synthetic vowel from the spectral envelope of my existing sample. (The eventual intention is to generate a simple tune) – The General Nov 11 '13 at 16:06

1 Answers1

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A possible approach is:

  1. Take a single period of the sample (identified visually). It is important that it begins and ends at 0 value (or very close) to avoid cracking noises caused by discintinuities at the each endpoints.
  2. Upsample or downsample the waveform extracted in step 1 period as necessary to get the desired pitch. Upsampling decreases pitch, downsampling increases it. You can use resample function for instance.
  3. Patch a lot of those periods one after the other until you get the desired duration of 5 seconds. You can use repmat function for that.
  4. Multiply that 5-second waveform element-by-element by a time-envelope with the desired shape. The envelope shape will typically be a fast attack in the form of a linear ramp from 0 to 1 , then a long constant value and then a decreasing ramp towards 0.

For increased realism you could introduce slow amplitude variations in the "constant" part of the envelope (tremolo effect). You could also extract in step 1 a piece of signal containing not one but several periods of the waveform. Those periods will not be exactly the same, and that will add "warmth" to the sound.

Luis Mendo
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