Answer 1—Yes. Delays of any value, including non-integer multiples of the sample period, can be created using FIR filters. If you envision the coefficients of a Nyquist low-pass filter (cut-off frequency is exactly half the sample rate) as points on a continuous impulse response of the FIR filter, then it’s pretty easy to see that resampling the continuous version of the impulse response at a different offset will yield a different delay for the filter. By choosing offsets that aren’t an integer multiple, it’s easy to see how a filter with a fractional delay can be constructed.

For example, a telecom project (wideband audio over a E1) once needed to be compatible with another older product. The audio signals were sampled at 16 and 32 kHz (periods of 62.5 and 31.25 µs, respectively). But interchannel delays of ±3 × N time slots (at approximately 3.91 µs per E1 time slot) for various small integer values of N were required (i.e., values of 11.72, 23.44, 35.16 µs…). This approached worked perfectly.

Contributor: David Tweed