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:

• Computational requirements are doubled during the cross-fade.
• The cross-fade should occur over a time interval long enough to yield a smooth result.
• The new delay interpolation filter, if any, may be initialized in advance of the cross-fade, for maximum smoothness. Thus, if the transient response of the interpolation filter is $N$ samples, the new delay-line + interpolation filter can be ``warmed up'' (executed) for $N$ time steps before beginning the cross-fade. If the cross-fade time is long compared with the interpolation filter duration, ``pre-warming'' is not necessary.
• This is not a true ``morph'' from one delay length to another since we do not pass through the intermediate delay lengths. However, it avoids a potentially undesirable Doppler effect.
• A single delay line can be shared such that the cross-fade occurs from one read-pointer (plus associated filtering) to another.