Litter (review)

Figure 5.

GRM Tools Pitch Accum interface screen.

If you are a Max/MSP user and long for a wider range of random number generators than are currently packaged with the application, Litter may be just the product for you. Litter is a collection of Max/MSP external objects consisting mostly of random number generators. It has been developed by the Berlin-based composer and software developer, Peter Castine. The collection was first implemented as a set of patchers but to increase the performance speed, they have now all been programmed as Max/MSP externals. A large number of the objects in the collection generate random number distributions, both discrete and continuous, that can be used for MIDI or other control purposes. These objects are accompanied by a set of signal generators for providing various types of noise, as well as mutation functions and some general utility objects. At current count there are more than 50 objects in total.

The inspiration for developing this collection came from Denis Lorrain's article "A Panoply of Stochastic 'Canons"' (Computer Music Journal 4/1, 1980), which details some random number distributions. Several other well-known statistical distributions of random numbers are also used. Many of the older random number generators use linear congruence algorithms to produce their output. These algorithms are not truly random and are slower than their more recently developed counterparts. The developer wanted to move away from the linear congruence methods used in the packaged Max/MSP random number generators. The result is a set of objects for generating 32-bit numbers, in which all bits can be random, using faster, more robust algorithms than are currently available in Max/MSP.

The discrete random number distributions include a Poisson distribution, a finite urn model, and a Bernoulli distribution, along with more fun objects for simulating dice-throwing and consulting the I Ching. The dice object allows you to throw a number of die with any number of faces. The I Ching object represents the throwing of yarrow sticks or the tossing of coins to prophecize on the present and the future. A linear congruence object is also included and is a good comparison to the main set of random number generators. Individual parameters can be set giving the user a high degree of control over the output. Two further uniform distribution objects are included, based on the Tausworthe 88 (T88) and Matsumoto and Kurita (TT800) algorithms. These extremely fast algorithms produce cycles of 2⁸⁸ and 2⁸⁰⁰-1 respectively, and generate numbers in which all bits are random. All of the random number generators in Litter can be auto-seeded or the user can supply a seed value.

The continuous random number distributions consist of well-known distributions such as Cauchy, Fisher, Gamma, Erlang, Weibull, log-normal, arc sine, beta, and Chi. A number of fractal distributions are also included. These are the control-domain equivalents of fractal noise-generator objects.

A wide range of noise generators are available to the user. As one would expect, objects are supplied for generating white and black noise but also for creating gray, brown, and pink noise, with two different algorithms used for the latter. A recent addition has been a very useful object that allows the user to control the type of noise generated by varying the values of fractal noise from 1/f to 1/f³. A noise-generator based on linear congruence methods, low frequency noise, popcorn noise, a Gaussian distribution, and a triangular distribution for creating dither, complete the set.

A number of mutation functions are also available in the collection. These are similar to those found in Tom Erbe's SoundHack program, and are based to a large extent on Larry Polansky's mutation functions implemented there. Both time and frequency domain mutation functions are available with a choice of algorithm...