Porting SGI Audio Applications to Linux

This article describes the process of porting a variety of audio applications from the SGI platform to the Linux operating system.
Releasing the Packages

I placed the ported programs and their sources on the Music Technology Department's FTP server at Bowling Green State University in Ohio, I then notified Dr. Hammer of our successes (he was pleased we had achieved so much), and I also advised NoTAM that their software was now available for Linux. NoTAM obtained the packages and placed them on their server, making the applications easily available to everyone. I also sent notices to the Csound mailing list and comp.os.linux.announce to inform the Linux community of the availability of these packages.

Since the releases were made public, development has continued. Working from our source packages and Richard's library code, the Swedish composer Reine Jonsson has contributed a version of Mix which now handles the popular WAV format sound files (the original Mix, along with the other NoTAM packages, supports only AIFF format files), while reducing loading times and enhancing playback smoothness (a critical factor on my 486/120). A new version of Ceres (see Figure 2) called Ceres2 is in development by Johnathan Lee and should be available in a Linux port by the time this article is published.

Figure 2. Ceres Screenshot

Further Development

Improvements can still be made: the applications ported so far are reasonably stable but will sometimes crash for no apparent reason. In some cases, not all of the original functionality is available, particularly if the package uses routines specific to the SGI's audio hardware capabilities. The Mix source code, for instance, includes calls to the SGI MIDI interface, but a replacement library for those calls has yet to be written. For now, I have had to disable the MIDI control code in the Mix sources. I have received a substantial amount of mail from users who have expressed interest in seeing more of this porting development, and my hopes are high that we will soon have a replacement for the SGI MIDI libraries to add to the audio and audiofile libraries already supported.

It must be mentioned that the NoTAM packages are not the only sources for high-quality UNIX audio-processing software available for possible porting. Guenter Geiger has successfully ported Paul Lansky's RT, another real-time, sound file mixer with excellent scripting capabilities. Work proceeds on ports of Paul Lansky's Ein (a DSP scratch pad), Mara Helmuth's Patchmix (a graphic patcher for the Cmix audio-processing language), and Russell Pinkston's XPatchWork (similar to Patchmix, but using the Csound language). Many other audio-related packages are available for Linux, and the interested reader should look at the Linux Soundapps web page for a continuously updated and comprehensive listing.

Final Thoughts

When I first used Linux I was thrilled by its possibilities, but dismayed by the lack of high-quality sound-processing software. Nevertheless, I was inspired by the availability of source code and the willingness of the Linux community to help develop audio applications. Since I am not a programmer, I relied on the skill, experience and advice of Linux users around the world. Like Linux itself, these projects were developed by a distributed collaborative effort, heavily dependent on the Internet for all communication, and built with freely available tools and libraries.

Thanks to Dr. Oyvind Hammer, Richard Kent, the LessTif developers and the XFree86 project, Linux audio software grows in quantity and quality almost daily. I encourage interested developers to contact me and let me know what they're working on or what they wish to work on. Many projects are waiting for developers who would like to contribute their talent and interest to the rapidly growing Linux audio and music software base.

Technical Considerations

by Richard Kent

When I first heard of Dave's project to port audio applications from an SGI-based environment to Linux, I was very interested in becoming involved—particularly because the sheer dearth of audio applications for UNIX was the primary reason for programming the Digital Audio Processor. I initially implemented DAP for SGI-based systems, but shortly before Dave contacted me, I successfully ported DAP to run in a Linux-based environment. (See Figure 3.) This experience helped greatly when porting the NoTAM applications. This sidebar is intended to detail the three main technical considerations when attempting such ports.

Figure 3. Digital Audio Processor