Winamp used to provide a Pitch/Tempo control in it's earlier versions. I was rather disappointed when I did not find it in the last version I installed. Then I remembered it was there in the SDK tutorial, and I thought I would just compile it for myself. I started to play with the code, and ultimately added ability to transform pitch or tempo independently, using a mathematical magic called Fourier Transformation.

The module actually contains two subroutines - one for changing the pitch independent of tempo (which actually uses the Fourier Transformation), and one for changing the tempo keeping the pitch/tempo ratio constant. Sometimes one or both of the subroutines may not be necessary. Then they will be turned off automatically, and a star (*) will appear beside the name.

You can mimic the Nullsoft Pitch/Tempo control by fixing the Pitch/Tempo ratio at 1.