What is Csound?

Csound is the most famous  sound synthesis language.
It can be considered one of the most powerful synths in the world.
CsoundAV is a version of Csound supporting not only audio and MIDI but also video and 3D graphics.

Csound Information

by Richard Boulanger and Barry Vercoe

Unlike today's commercial hardware synthesizers, which have a limited set of oscillators, envelope generators, filters, and a fixed number of ways in which these can be interconnected, Csound's power is not limited. If you want an instrument with hundreds of oscillators, envelope generators, and filters you just type them in. More important is the freedom to interconnect the modules, and to interrelate the parameters which control them. Like acoustic instruments, Csound instruments can exhibit a sensitivity to the musical context, and display a level of "musical intelligence" to which hardware synthesizers can only aspire...

...Realizing music by digital computer involves synthesizing audio signals with discrete points or samples that are representative of continuous waveforms. There are several ways of doing this, each affording a different manner of control. Direct synthesis generates waveforms by sampling a stored function representing a single cycle; additive synthesis generates the many partials of a complex tone, each with its own loudness envelope; subtractive synthesis begins with a complex tone and filters it. Non-linear synthesis uses frequency modulation and waveshaping to give simple signals complex characteristics, while sampling and storage of natural sound allows it to be used at will.

Since comprehensive moment-by-moment specification of sound can be tedious, control is gained in two ways: 1) from the instruments in an orchestra, and  2) from the events within a score.

An orchestra is really a computer program that can produce sound, while a score is a body of data which that program can react to. Whether a rise-time characteristic is a fixed constant in an instrument, or a variable of each note in the score, depends on how the user wants to control it.

The instruments in a Csound orchestra are defined in a simple syntax that invokes complex audio processing routines. A score passed to this orchestra contains numerically coded pitch and control information, in standard numeric score format. Although many users are content with this format, higher level score processing languages are often convenient.

The programs making up the Csound system have a long history of development, beginning with the Music 4 program written at Bell Telephone Laboratories in the early 1960's by Max Mathews. That initiated the stored table concept and much of the terminology that has since enabled computer music researchers to communicate. Valuable additions were made at Princeton by the late Godfrey Winham in Music 4B; my own Music 360 (1968) was very indebted to his work. With Music 11 (1973) I took a different tack: the two distinct networks of control and audio signal processing stemmed from my intensive involvement in the preceding years in hardware synthesizer concepts and design. This division has been retained in Csound.

Because it is written entirely in C, Csound is easily installed on any machine running Unix or C. At MIT it runs on VAX/DECstations under Ultrix 4.2, on SUNs under OS 4.1, SGIs under 4.1, and on the Macintosh under ThinkC 4.0. With this single language for audio signal processing, users move easily from machine to machine.

The 1991 version included many new features. I am indebted to others for the contribution of the phase vocoder and FOF synthesis modules. That release also charted a new direction with the addition of a spectral data type, holding much promise for future development. The 1992 release is even more significant for its addition of MIDI converter and control units, enabling Csound to be run from MIDI score-files and from external MIDI keyboards. Since the newest RISC processors bring to computer music an order of magnitude more speed than did those on which it was born, researchers and composers now have access to workstations on which realtime software synthesis with sensing and control is now a reality. This is perhaps the single most important development for people working in the field. This new Csound is designed to take maximum advantage of realtime audio processing, and to encourage interactive experiments in this exciting new domain.