Tech Page: Spontaneous Playback

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FIG. 1: In Musinaut''s MXP4Creator, you assign weighting factors to each version of each section of the song, which determines how often each version will be played.

Live music is quite different from the visual arts. For example, every time a given song is played, it is unique, with inevitable variations from one performance to the next. As Joni Mitchell once noted, no one ever asked Van Gogh to paint The Starry Night again. But many musicians are expected to play certain songs at each of their concerts, and these songs sound different every time. On the other hand, recorded music is more like a painting — once it's in the can, it sounds exactly the same each time it's played.

Now, a new audio format could bring recorded music closer to the live-performance experience. This new format, called MXP4, is being developed by the French company Musinaut (, which rhymes with astronaut. Like those intrepid pioneers of outer space, Musinaut is exploring the uncharted frontiers of recorded music with heretofore unheard-of capabilities.

The basic idea is this: song files saved in the MXP4 format will sound different each time they are played. For instance, you might hear a different guitar solo or verse arrangement. In addition, the changes need not be entirely predictable, lending a dynamic freshness to the song each time it's heard.

As the composer/performer, you start by recording a song in the normal manner, using any recording program you like, such as Digidesign Pro Tools, Apple Logic, or Steinberg Cubase. During this process, you record multiple takes of the song or song sections, such as the intro, verses, choruses, bridges, solos, and endings. For example, some versions might use acoustic instruments whereas others use electric, and some might have different musical styles.

Once all the versions of the song and its sections are recorded, you export the tracks separately to WAV or AIFF files and then open them in MXP4Creator, an application developed by Musinaut for Windows and Macintosh computers. Next, you mark the boundaries of each song section, which are called patterns in MXP4-speak. In addition, you group all related sections together; for instance, all the variations of each verse are grouped into a single entity. These entities are called tracks, and the different audio versions within a track are called subtracks.

You then assign weighting factors to each subtrack, which determines how often it will be played with the song (see Fig. 1). For example, say you have three guitar solos, and you want one of them to be heard more often than the others. You might specify a weighting factor of 50 percent for that subtrack and 25 percent for each of the other two. You can also assign weighting factors to the order in which patterns are played and even link the end back to the beginning, creating a song of indefinite length and constant variation.

Finally, you save the entire project as an MXP4 file that can be played on a computer with the appropriate software player or streamed from a Web site using Musinaut's streaming software (check out the examples on the company's site). Each time the file is played, you hear a different version of the song. Within MXP4Creator, you can also define what Musinaut calls a skin, which narrows the choices of subtracks to those that fit a particular style or mood — say, electric or acoustic — that listeners can choose according to their preference.

MXP4Creator and the streaming software are available now, but Musinaut has big plans for the future, including integrating MXP4Creator into programs such as Pro Tools, applying the MXP4 idea to MIDI files, and developing a portable player similar to the iPod. This is a very exciting idea that brings spontaneity to recorded music, and I intend to keep a close eye on it.