Large Delay Changes

When implementing large delay-length changes (by many samples), a useful implementation is to cross-fade from the initial delay line configuration to the new configuration.

• Computation doubled during cross-fade
• Cross-fade should be slow enough to sound smooth
• Not a true ``morph'' from one delay length to another, since we do not pass through the intermediate delay lengths
• A single delay line can be shared such that the cross-fade occurs from one read-pointer (plus interpolation filtering) to another
• Typically used with a cross-correlator that looks for good cross-fade delays (where cross-correlation is maximized)
  • Used in Synchronous OverLap Add (SOLA) methods for Time Scale Modification (TSM) and Frequency Scaling
  • Used (originally?) by the Eventide Harmonizer
    (Frequency Scaling)

  • Can alternatively do a power cross-fade (instead of the usual amplitude cross-fade) where the cross-correlation is at a minimum in magnitude¹