Mark Dal Porto, Texas Woman's University

How is music technology being used today to inspire creative applications in music? In this paper, I focus in on the exciting new union of MIDI with digital audio applications.

The integration of MIDI and digital audio is one of the more recent and significant technological developments for musicians. The ever-increasing power of desktop computers, combined with the advent of inexpensive, dedicated sound hardware that can be added to a computer, has resulted in a much closer pairing of these two worlds of sound manipulation. As software appears that brings MIDI and digital audio together, an enormous realm of creative possibilities is opening up. By taking advantage of both the efficiency of MIDI and the flexibility of digital audio, these tools open up new dimensions of creative expression in the classroom and for the computer composer.

There are numerous practical advantages to controlling both MIDI sequencing and digital audio recording simultaneously. MIDI composers are used to cutting and pasting musical events as easily as paragraphs in a word processor, and the tools for doing so have become highly sophisticated and friendly. Extending that metaphor to blocks of digital audio is a major advantage. For example, digital audio can also be processed and mixed non-destructively in the same way that MIDI tracks can be faded, panned, or processed, using velocity and controller commands within the sequenced data.

It is now much easier to conceptualize both MIDI and digital audio together. Integrated programs display audio and MIDI tracks simultaneously onscreen, giving the composer or sound designer instant visual feedback on the structure of a piece, either as an overview, or at the microscopic editing level. Instead of being separate entities that happen to be synchronized, the audio and MIDI data can be seen as a single compositional entity, giving the composer a vastly improved platform for creativity.

The dreamed-of integration of digital audio and MIDI is being realized from several directions at once. Sequencing software is now available that adds audio recording and editing with MIDI, and hard disk recording systems are integrating MIDI recording, playback, and manipulation tools. In addition, more esoteric systems outside of the music industry mainstream are combining the two technologies in unusual and potentially revolutionary ways.

The most powerful software sequencers now include the ability to edit and manipulate digitally recorded sounds along with MIDI data. These software programs that incorporate the ability to record and edit both MIDI and digital audio information simultaneously are called "digital audio sequencers." If the computer on which the sequencing program is run is also equipped with the accessories required for hard-disk recording, then two or more tracks of a digital recording can be incorporated into the sequence. This provides unprecedented opportunities for integrating MIDI, acoustic, sampled, and electronically synthesized sound sources into a single project.

Separate digital audio and sequencer programs can also be used simultaneously to playback both digital audio and MIDI sequenced material. By syncing the MIDI sequencer to the digital audio program via MIDI Time Code, both programs can playback together. This is accomplished by having either the MIDI sequencer or digital audio program sending out MIDI time code during playback. The other program is then set to follow this time code and playback in synchronization with the other.

MIDI Time Code is (commonly referred to as "MTC") is based on the passage of absolute time and is independent of musical tempo. MIDI Time Code was adopted as a means of representing, with specifically defined MIDI messages, the absolute time code information contained in a SMPTE (pronounced "simpty") signal. (SMPTE is an acronym for Society of Motion Picture and Television Engineers, an organization that developed this form of time coding to facilitate the production of television and other video programming.) A SMPTE time code signal is actually an audio signal, so that it can be magnetically recorded, that provides a continuous stream of information marking the passage of time on tape. The information includes, among other things, the hours, minutes, seconds, and frames (a subdivision of the second). By using MIDI Time Code derived from the SMPTE time code signal, a separate sequencer program may be synchronized with a digital audio program. Hence, a separate MIDI sequencer playing MIDI synthesizers may be combined with a digital audio program playing recorded sound all at the same time.

Experimental musicians working in universities or other non-commercial studio environments are thrilled at the prospect of working with complex and infinitely variable digital sound "objects" as flexibly as they work with the more-restricted parameters of MIDI. However, this way of producing music is not just available to these institutions of research. This way of producing music has been accessible for some time now all the way down to the general consumer who may simply wish to combine MIDI with digital audio in such things as video, multi-media applications, or games.

From a hardware standpoint, the key to integrating MIDI and digital audio has been the development of sound-recording and sound-generating hardware placed inside the computer that is handling the MIDI data. Its bandwidth over sixteen channels of data is limited to 31,250 bits per second, which is trivial for a computer whose CPU is ticking at several million clock cycles per second. Audio, however, is much more demanding, and bandwidths in excess of 1.5 million bits per second are possible with just two tracks.

Audio, therefore, is often produced by a plug-in card that can handle all the sound-generating calculations itself and be addressed by the computer over a relatively slow data bus, thus taking a great burden off of the computer's central processing unit (CPU). The major differences between the various products available, besides the platforms they are designed for, have to do with the method and speed of data transfer and the audio quality. These differences are in terms of sampling rate (which controls frequency response) and word length or number of bits resolution (which determines dynamic range).

The technology explosion of the last two decades has brought down many barriers, including that between MIDI and digital audio. Many different hardware and software companies are gearing their developments toward integrating these two ways of producing music in ways previously undreamed of. By taking advantage of both the efficiency of MIDI and the flexibility of digital audio, the new tools open up new dimensions of creative expression for the computer composer.

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Articles

Burger, J., & Hall, G. (1991, January). Sync of swim. Electronic Musician, 60-67.

De Furia, S., & Scacciaferro, J. (1987). The sampling book. Pompton Lakes, NJ: Third Earth.

The Music & Computer EducatorFreeman, P. (1994, April). All for one. Electronic Musician, 30-52.

807 E. Jericho TurnpikeFryer, T. (1989). A practical approach to digital sampling. Milwaukee: Hal Leonard.

Huntington Station, NY 11746Hurtig, B. (Ed.). (1987). Synthesizers and Computers, (Rev. ed.). Milwaukee: Hal Leonard.

Phone: (516) 385-7107Miller, D., & Lehrman, P. (1991, December). When worlds collide -- Integrating MIDI and digital audio. Electronic Musician, 44-60, 123.

Pohlmann, K. C. (1989). Principles of digital audio, (2nd ed.). Indianapolis: Howard W. Sams.

Pogue, D. (1993, January). Multimedia minus one. Electronic Musician, 51-61.

Pressing, Jeff. (1992). Synthesizer performance and real-time techniques. Madison, WI: A-R Editions.

Rothstein, J. (1992). MIDI: A comprehensive introduction. Madison, WI: A-R Editions.

Rumsey, F. (1990). MIDI Systems and control. London: Focal Press.