Sequential waveform composition

Sequential waveform composition works by letting the computer generate sample pattern sequences according to a user-defined formula. The patterns need not be a single wavecycle or a waveset. In fact, the whole sequence would not necessarily need to form any pattern at all. Some patterning is, however, desirable here because a minimum degree of repetition is indispensable for the production of a waveform. In other words, repetition is necessary because it determines the form of a waveform, otherwise the outcome will always be white noise. 

In essence, the technique resembles the statistical wavecycle synthesis technique introduced earlier, with the fundamental difference that here the breakpoints are deterministic, in the sense that the segments are defined explicitly rather than statistically. Despite the deterministic nature of the technique itself, its outcome is often unpredictable, but notwithstanding interesting and unique. Like the binary instruction technique discussed in Chapter 2, synthesis by sequential waveform composition is also commonly referred to as non-standard synthesis. Indeed, in order to work with this technique one needs to be prepared to work with non-standard ways of thinking about sounds, because its s)mthesis parameters by no means bear a direct relation to acoustics. 

The composer Arun Chandra, based in Illinois, USA, is one of the main supporters of the sequential waveform composition technique (Chandra, 1994). He has devised Wigout and TrikTrak, a unique pair of programs for PC-compatible platforms, specifically designed for sequential waveform composition. Both programs, plus a number of examples and a comprehensive tutorial - specially prepared for this book by Arun Chandra himself - are available on the accompanying CD-ROM (in the folder wigtrik). 

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Synthesis by binary instruction is a curious technique developed in the 1970s at the Institute of Sonology in the Netherlands. This technique is commonly known as non-standard synthesis, but in this book we prefer to use the more specific term - binary synthesis - in order to distinguish it from other methods that could also be classified as non-standard for example, Walsh synthesis and sequential waveform composition (discussed in Chapter 5). 

Essentially, the technique works by specifying a collection of elements and by arranging these elements in a sequence that together comprises the waveform hence the name sequential waveform composition. A variation of the waveform portrayed in Figure 5.27 could be defined using the same four elements as follows (Figure 5.28) element 2 + element 4 + element 1 + element 3 + element 1 + element 4 + element 3. 

Wigout and TrikTraks form a system for PC-compatible platforms (MS-DOS and Windows) specifically designed for sequential waveform composition (see Chapter 5). The system was designed by the composer Arun Chandra in collaboration with researchers of the School of Music at the University of Illinois, USA (Chandra, 1994). 

Wigout works by generating sequences of sample segments that, taken together, compose a waveform. It can generate complex combinations of waveforms of arbitrary length, limited only by the amount of memory on the computer (see Chapter 5 for more details about the sequential waveform composition technique). 

Finally, time-based techniques approach synthesis from a time domain perspective. The parameters of time-based synthesis tend to describe sound evolution and transformation of time-related features e.g. in terms of time lapses. Examples of time modelling techniques include granular synthesis and sequential waveform composition time modelling techniques are discussed in Chapter 5. 

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