Csound for Linux

Csound is a music composition and sound programming language originally written by Barry Vercoe at MIT. As Nick Bailey pointed out in his October 1998 LJ article “Sculptor: A Real Time Phase Vocoder”, Barry's original MUSIC11 program was eventually ported from PDP-11 assembler to UNIX C, where it became Csound. MUSIC11 was derived from the pioneering MusicV program by Max Mathews, perhaps the most revered “Founding Father” of computer music technology.

One of MusicV's major innovations was the implementation of the unit generator, a “black box” concept that allowed great extensibility to the language. A unit generator can be a signal generator or modifier, a patching opcode, a sensor, or it can provide sound file I/O and signal display types. Csound has evolved into a notable successor to Music V, quickly accommodating new synthesis methods and DSP algorithms. It is now at the cutting edge of modern computer music software. Linux Csound has done more than simply kept pace with that evolution—it offers capabilities not found with versions available on other platforms.

In 1996, I wanted to try out the Linux OS. I knew certain software synthesis languages would run under it, and those languages were not available for DOS/Windows machines. Although Csound does indeed run under Microsoft operating systems (and many others), I was interested in seeing how well it would run under Linux. Jonathan Mohr had already added the real-time audio support for Linux, but I immediately discovered I had stumbled upon another big “DIY” (do it yourself) project. The source code available from the Bath, UK FTP site (the primary repository for the “canonical” packages) was a general UNIX package, without Linux-specific Makefiles or any other compilation amenities. Although I was a novice at both Linux and the C programming language, I jumped in and started thrashing. With good assistance from John Fitch (maintainer of the Bath site and the canonical sources) and the helpful members of the Csound mail list, I finally produced a working set of Makefiles for the entire source tree. I soon had a fast Linux Csound with full support for X displays, real-time audio output and all the current opcodes. Professor Burton Beerman kindly provided an FTP site for my Linux Csound packages on his MusTec server at Bowling Green State University, and for two years I maintained the public version on that site and at Bath.

CSound in a Nutshell

Early in 1998, I received a message from Professor Nicola Bernardini at AIMI (Associazione di Informatica Musicale Italiana). He had thoroughly rewritten the Linux Csound Makefiles and wondered if I might be interested in adding them to the source package. His offer came at a good time, as I knew the code maintenance needed a more solid structure. Nicola's expertise was just the right factor appearing at just the right moment. His Makefiles enabled me to quickly prepare a variety of distribution packages (with or without X support, static build or shared lib, real-time audio enabled/disabled, etc.) and compile a more complete build of the source tree. Most importantly, the Makefiles created libcsound.so, a shared library which drastically reduced the binary's memory footprint (from about 450KB to less than 20KB).

Real-time Linux CSound

Around the same time, developer Gabriel Maldonado wrote a set of MIDI output opcodes, allowing Csound to be used as a MIDI composition/control instrument. Csound already accommodated MIDI input, directly from /dev/midi or from a Type 0 Standard MIDI File (see Real-time Midi Input). Gabriel's opcodes are different: they permit exploration into MIDI composition algorithms simultaneously with the rest of Csound's real-time I/O. Hypothetically, it would be possible to have a MIDI device controlling one Csound instrument while another instrument sends its output to devaudio. Given support for a full-duplex sound card, it should even be possible to have asynchronous I/O for both the MIDI and the audio ports.

Alas, no routines had been written for Linux Csound that would accept the data from Gabriel's opcodes and send it out to the MIDI port. After studying John Fitch's code for the Windows Csound MIDI output handler, I decided to try writing the appropriate calls for Linux. I fumbled around with the OSS/Free API and eventually wrote the code needed to activate the requested MIDI interface and accept the control data sent to it from the Maldonado opcodes. Linux Csound was as up-to-date as any other version, and the necessary code for MIDI output had been trivial to write, consisting primarily of a few calls to the sound card API macros.