Fixed-length variable-step delay lines keep decay time constant across pitch, unlike variable-length lines

A digital delay line can be built two ways: variable length with a constant time step, or fixed length read at a variable step rate. The choice matters for physically modeled strings. With a variable-length / fixed-step line, shortening the line to raise pitch also shortens the number of feedback passes per second in a way that makes the decay time scale with pitch — high notes die away faster than low notes. But on a real guitar, high and low strings have roughly the same decay time. A fixed-length / variable-step line decouples the two: pitch is set by the readout step rate while the decay depends on the (fixed) averaging speed, so a single 256-sample table can cover sub-audio to over 20 kHz with pitch-independent decay. The design trade-off is that fixed-length variable-step lines need interpolation between samples, which the hardware may not support (the Nord Modular offers only variable-length fixed-step lines).

Examples

Fixed-length 256-sample table read at a variable step: pitch from very low to >20kHz with uniform decay, matching a real guitar where high and low strings ring for similar durations.

Assessment

Explain why a variable-length fixed-step delay line makes high notes decay faster than low notes. State which delay-line type you would choose to model a guitar and why.