VFX Article, Chapter 4

4. Program 2, Echo

The Echo effect is accomplished by the VFX processor very easily using a simple algorithm which is a digital implementation of an adjustable length analog delay line. The Echo block diagram (Figure 5) explains the algorithm. The input signal from the microphone is sampled at an 6.5 Khz rate. It is then summed with the delayed signal received n*455 periods ago where n goes from nine to zero (n is displayed on the LED display). The delay line is implemented in 4k of external SRAM. The software allows the adjustment of the delay from .63 to 0 msec.

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