DAFX: Digital Audio Effects, Second Edition

6.5 Time Shuffling and Granulation

6.5.1 Time Shuffling

Introduction

Musique concrète has made intensive use of splicing of tiny elements of magnetic tape. When mastered well, this assembly of hundreds of fragments of several tens of milliseconds allows an amalgamation of heterogeneous sound materials, at the limit of the time discrimination threshold. This manual operation, called micro-splicing, is very time-consuming. Bernard Parmegiani suggested in 1980 at the Groupe de Recherches Musicales (GRM) that this could be done by computers. An initial version of the software was produced in the early 80s. After being rewritten, improved and ported several times, it was eventually made available on personal computers in the form of a program called brassage in French that will be translated here as time shuffling [Ges98, Ges00].

Signal Processing

Let us describe here an elementary algorithm for time shuffling that is based on the superposition of two time segments that are picked randomly from the input signal (see Figure 6.22):

1. Let x(n) and y(n) be the input and output signals.

2. Specify the duration d of the fragments and the duration D ≥ d of the time period [n − D, n] from which the time segments will be selected.

3. Store the incoming signal x(n) in a delay line of length D.

4. Choose at random the delay time τ1 with d ≤ τ1 ≤ D.

5. Select the signal segment x1d of duration d beginning at x(n − τ1).

6. Follow the same procedure (steps 4 and 5) for a second time segment x