Digital Resampling and Interpolation
Here's a wonderful tutorial on how to do digital resampling and interpolation in general.
You'll also find, within the rtl directory, examples of a nearest
neighbour interpolator, a
linear upsampling interpolator,
and a quadratic upsampling interpolator.
All three have been discussed on the ZipCPU blog: the nearest neighbour interpolator here, the linear interpolator here, and the quadratic interpolator here.
If time permits, I look forward to adding some higher order interpolation solutions and/or splines to this repository.
The tutorial is offered here under the Creative Commons, Attribution-NoDerivations 4.0 International license.
If these conditions are not sufficient for you, other licenses terms are available for purchase.