Fascinating question... You can get very small delays from allpass filters, but they're frequency-dependent (i.e., the group phase delay depends on frequency.) There are probably other interpolation schemes that could get fractional delays (fit a polynomial through the points you have, 1 to the right and n-1 to the left, for instance) but they won't have a flat frequency response. So one could probably devise trade-offs that sounded OK, at least at low frequencies.
If the aim is to make a recirculating delay network with very low delay, the best way is probably to resample to a much higher sample rate, do the job, and then resample back down.
cheers Miller
On Fri, May 14, 2004 at 11:28:16AM -0400, Larry Troxler wrote:
On Fri, 14 May 2004, Frank Barknecht wrote:
Thinking of tapes as simple sample recorder/players or even as some kind of adc/dac combination, they must follow the same rules as other samle players, that is: the max frequency they can record or play is Nyquist frequency, that is half sample rate. The shortest possible delay time then in theory is 1/nyquist[Hz] seconds.
Is it? Using a fractional interpolating all pass filter, you can't acheive delays less than one sample? Or does the allpass filter let you get fractional delays, but still the minimum delay is one sample?
Larry Troxler
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