Fractional Delay Filter
Today I have a Thiran all-pass filter that can be used as a fractional delay line to share with you all. It has a simple yet interesting and useful effect on incoming audio signals – it can delay them by 1.5 – 2.5 samples (using a normal delay line you would be limited to using only integer values). To achieve a longer delay than 2.5 samples, you can simply wire it after a delay line.
Fractional delay lines have various musical applications – they are useful in bandwidth limited oscillators, comb filters, Karplus-Strong and other physical modeling algorithms, and probably many other things that I am not aware of. My interest was first piqued by this article, and much of the recent research on fractional delay filters seems to be by Vesa Välimäki.
Hopefully I’ll have another project or two that uses this later in the week.