Purpose

What’s the point? Why bother? Why is a definition important?

Professional game composers and music programmers are faced daily with (LOTS of) immediate, practical concerns. Students and amateurs trying to break in to the industry are frustrated by difficulties involved in getting any applied experience scoring games. Calls for articles on game topics focus on papers with practical, “how-to” solutions. (C.f. the Gamasutra.com Writers Guidelines) Who has time for theoretical exploration?

A definition exercise challenges our assumptions about the craft, and offers fresh perspective. It scopes and frames the problem in a way that helps us start looking for underlying causes and real long-term solutions, getting us out of the mindset of temporary hack fixes and implementation-specific details. A deep understanding of the problem space is an invaluable asset in any discipline. In a way, a formal definition starts teaching us “how-to” think about a field.

Challenging Assumptions

“What is adaptive music?” is one of those questions like: “What is music?” or “What is art?” Everyone takes for granted that they know what art is – until they show up to the first day of Art History 101 and their professor asks the class to define it.

As it turns out, it is almost impossible to define music without referencing preexisting notions of music. “Rhythmic patterns of notes” seems plausible at first… except that some cultures’ music doesn’t have any kind of concept of rhythm, and others’ don’t recognize pitch – let alone notes. “Organized patterns of sound in time” is better in the sense that it is less culture-specific. After all, organization is subjective. (For instance, the way that I like to organize my living space drives my wife mental. And vice versa.) On the other hand, “patterns” implies repetition, and some musical traditions are organized around strictly non-repetitive, organic growth. More importantly, the definition doesn’t differentiate music and, well, speech. Hmm.

To a certain extent, we simply know what music is because we grew up in a musical culture. And, in general, unless you’re into ethnomusicology or philosophy, that’s about all you need to know; a formal definition is not really that useful.

“Adaptive music” is different – a formal definition really is that useful. You did not grow up with an innate cultural understanding of this concept. If you want more than a superficial glimpse of its essential nature, you’re going to have to dig.

Understanding the Problem Space

For me, the process of defining adaptive music was a door-opening “aha! moment”. It provided a solid foundation for further research and exploration, and led to a number of later “aha! moments”. It provided the basis for the identification of some easily-overlooked but important fundamental truths about the art of adaptive music, which will be the topic of future articles.

Most importantly, this knowledge has been of practical value in applied game production situations.

But as I said before, your mileage may vary.

Proposing a Definition

This section gives proposes a formal definition of adaptive music in a couple of different formats.

Definition

Adaptive music is music in which a primary concern in its construction is a system for generating significantly different performance versions of a piece in response to a specified range of input parameters, where the exact timing and/or sequence and/or quantity and/or presence and/or values of input parameters are not predetermined, and where the desired output of the system is coherent and aesthetically satisfying within the musical tradition(s) selected by the composer.

Definition (redux)

For some reason I love the almost impenetrable density of the single-sentence, dictionary-style adaptive music definition. On the other hand, it has been pointed out to me that: A) it’s almost impenetrably dense, B) it’s probably not even English, and C) that for complex concepts, it can be a better idea to provide a bullet-point-style list of defining criteria. So, for those who prefer that kind of thing:

• adaptive music incorporates a system for generating significantly different performance versions of the piece

• the generation system is driven by pre-specified input parameters

• the actual performance-specific events are expected to have a significant degree of indeterminacy

• traditional musical coherency and organization is a priority

Exploring the Definition

As it turns out, the definition itself was rather boring, pedantic, and academic. But let’s take a look at the pieces, and see what we learn.

Adaptive music incorporates a system for generating significantly different performance versions of the piece

Or, in other words, “a primary concern … is a system for generating significantly different versions of a piece”.

In the real world, no two performances of any piece of music are ever exactly the same. Consider that even when listening to a CD player under fairly controlled conditions, subtle variations in room temperature, air pressure, background noise, the listener’s head position, heart rate, blood sugar levels, prior experience with the piece (is this the first listen? Or do you have the thing memorized? Was it once “our song”?), and mental state (to name a few factors) all introduce variation in the way a piece is heard. In live performance, variability is much more pronounced. When listening to even a virtuoso performer, variations in the exact execution of a piece of music are to be expected.

The key determining factor in adaptive music is intent. If my piano student massacres a Beethoven sonata (perhaps even, in the process, creating a number of very interesting structural and dynamic variations), it is still not a piece of adaptive music. It was intended by Beethoven to sound a certain way. Composed linear music can be said to have a single representative form. Any given performance is an expression or interpretation of this single, static ideal.

Adaptive music, by contrast, is significantly different from performance to performance by design. The form of a piece of adaptive music as it is expressed in a given performance is essentially flexible. Individual expressions of a piece of adaptive music can be quite different from each other, but each is equally representative of the composition.

The generation system is driven by pre-specified input parameters

The fact that variations are generated “in response to a specified range of input parameters” contains two important ideas. The first is that the system is, in fact, driven by external interaction. The second is that the exact nature of these interactions is carefully designed.

Adaptive music relates specific events (or ranges of events) to variations in the musical performance. An adaptive music system enumerates these events and describes how they are to be handled.

The actual performance-specific events are expected to have a significant degree of indeterminacy

“The exact timing and/or sequence and/or quantity and/or presence and/or values of input parameters are not predetermined.” This describes the “random” nature of adaptive music. At the time of construction, the exact details of which events will arrive when and how are left to be decided at the time of performance. The final form of the piece that is expressed at performance time is generated in response to indeterminate events.

Potentially, even tiny input variations can have a drastic impact on the musical output of an adaptive system. But remember that the system is designed to handle specific events. This means that given the exact same input parameters, the exact same output is generated. Adaptive music is in this sense is ultimately deterministic.

Traditional musical coherency and organization is a priority

“The desired output of the system is coherent and aesthetically satisfying within the musical tradition(s) selected by the composer.” In other words, ideally, each generated instance of a piece of adaptive music would sound as good as if it were linearly composed. A primary goal is for every performance of the system to work aesthetically as a piece of music.

Randomness as an aesthetic goal is not a defining characteristic of adaptive music. Randomness for randomness’ sake is not part of this tradition.