Variability

An interesting side effect of the performance of recorded music production is the absence of variation in playback. Songs on a CD play back the same every single time. Music written to take advantage of DirectMusic's variability properties can be different every time it plays. Variation is particularly useful in producing music for games, since there is often a little bit of music that needs to stretch over many hours of gameplay. Chapter 21 discusses applications of variation in music production outside the realm of games.

The imperfection of the living, breathing musician creates the human element of live musical performances. Humans are incapable of reproducing a musical performance with 100 percent fidelity. Therefore, every time you hear a band play your favorite song, no matter how much they practice, it differs from the last time they played it live, however subtle the differences. Repetition is perceived as being something unnatural (not necessarily undesirable, but unnatural nonetheless) and is easily detectable by the human ear. Variability also plays a role in song form and improvisation. Again, when a song is committed to a recording, it has the same form and solos every time someone plays that recording. However, when performed by musicians at a live venue, they may choose to alter the form or improvise in a way that is different from that used in the recording.

DirectMusic allows a composer to inject variability into a prepared piece of digital audio, whether a violin concerto or an audio design modeled to mimic the sounds of a South American rain forest. Composers and sound designers can introduce variability on different levels, from the instrument level (altering characteristics such as velocity, timbre, pitch, etc.) to the song level (manipulating overall instrumentation choices, musical style choices, song form, etc.). Using DirectMusic's power of variability, composers can create stand-alone pieces of music that reinvent themselves every time the listener plays them, creating a very different listening experience when juxtaposed to a mixed/mastered version of the same music. Composers alter the replay value of their compositions as well by allowing their music to reinvent itself upon every listening session.

Avoidance of audio content repetition in games is often important. When asked about music for games, someone once said, "At no time in history have so few notes been heard so many times." Repetition is arguably the single biggest deterrent to the enjoyment of audio (both sound effects and music) in games. Unlike traditional linear media like film, there are typically no set times or durations for specific game events. A "scene" might take five minutes in one instance and hours in another. Furthermore, there is no guarantee that particular events will occur in a specific order, will not repeat, or will not be skipped entirely. Coupled with the modest storage space (also known as the "footprint") budgeted for audio on the media and in memory, this leaves the audio producer in a bit of a quandary. For the issue of underscore, a game title with hours of gameplay might only be budgeted for a few minutes worth of linear music. The audio director must develop creative ways to keep this music fresh — alternative versions, version branching, and so on. Audio programmers can investigate and implement these solutions using DirectMusic.

As to events triggering ambience, dialog, and specific sound effects, these may repeat numerous times, adding the challenge of avoiding the kind of obvious repetition that can spoil a game's realism for the player. As we discuss in more detail, DirectMusic provides numerous methods for helping to avoid repetition. On the most basic level, audio programmers can specify variations in pitch and multiple versions of wave, note, and controller data. Even game content (specific scripted events in the game for instance) can specify orderings for playback (such as shuffling, no repeats, and so on) that DirectMusic tracks as the game progresses. Using advanced features, chord progressions can maintain numerous potential progression paths, allowing a limited amount of source material to remain fresh even longer.