Musical Techniques for Interactivity

Musical Techniques for Interactivity

Making the Game Better A World of Uncertainty Requires A Different Approach That May Be More Complex But Need Not Be More Difficult Just Different A Few Specifics A Tip About Tips

In a film score a composer always knows what the music should be evoking at any point in time based on what is happening in the film. The very definition of interactivity prevents this. Usually the composer cannot know in advance what will be happening at any particular moment in a game. He could be aware that there might be a moment where a player is winning or another moment where a player is losing but he cannot know which will happen first or for how long.

A common solution to this problem is to design short segments of music that represent either winning or losing. The game program then has to trigger them at the right time. This one situation exposes several problems often encountered in composing music for interactivity. If the musical phrases are long and they are to finish before the next is played then there will be a lag between the time when the situation for the player changes and the music reflects that fact. One solution is to interrupt the first piece of music and jump immediately to the second the moment the situation changes. This is not only un-musical but will sound terrible if the situation changes often. Another solution is to make the segments very short so that when the situation changes there will not be a long wait for the first segment to end so the next one can begin. Unfortunately randomly organized short phrases have even less musical value then randomly organized long phrases. Yet another solution is a bit more complicated. It involves designing a composition with one portion that is always playing from beginning to end no matter what the situation while several other layers are added or subtracted from moment to moment as the game state changes. Picture a nice jazz combo playing the whole time while occasionally an even-tempered sax or a burning guitar or mellow flute jump in and out of the fray. Without proper controls this tends to sound like a badly organized jam session. The necessary controls include a way to cause the soloists to enter and exit at musically appropriate places like at bar lines. But music must also be designed so that either the soloists can all play at the same time without stepping on each other's feet or so that no more than one soloist is playing at the same time.

I like to use a train analogy to describe the above situation but this requires you to imagine that you will find several sets of train tracks all running next to each other. Picture several trains all travelling in the same direction alongside each other. Each train represents a group of instruments or a level of excitement in a musical composition. Each boxcar contains a few measures of music. You are standing at a fixed point representing the place where it is decided which music should be fed to the synthesizer for playback. You do this by selecting which train you will follow with your eye. You may only switch trains between boxcars. Now that we have established in the analogy I can say something about its characteristics.

We could be describing a single piece of music with several layers that can all be played together or separately. Or we could be describing several pieces of music that are similar so we can jump between one and the next but which cannot be played all at the same time. In the past a technical limitation of the drivers usually meant that all of the music had to be played through the synthesizer at the same time. The cars were selected by simply turning up their volume. This meant that out of 24 voices available in a synthesizer only about eight could be used at any one time resulting in a small musical group sound. For software synthesizers this is a less than desirable situation since they eat up CPU capacity like Pac Man.

Since you may be jumping from one train to another between cars each car has to contain only notes that begin and end within the boundaries of one car. This means that notes that carry across car boundaries are not allowed. You cannot be sure that a phrase begun in the first car in train 'A' will be followed by the end of that phrase in the second car of train 'A'. Therefore you must be sure that any phrase that carries from one car to the next will end properly no matter which train you switch to. One of the strengths of this scheme is that the composer can design a flow of excitement or emotion throughout the length of the train even though he cannot know which particular notes will carry these emotions. This is because a musical flow is achieved by the way the notes flow from car 1 to car 2 and the emotional state is changed by whether you are playing the version that is in train 'A' or train 'B'. Emotional change is achieved by switching trains at the right moment and not by a change in the music on the original train. The musical flow of the piece is a result of the way notes flow from one car to the next. You will not be changing the numerical order of the cars the musical flow can be planned in advance but since you may be switching back and forth between trains each train must be laid out with a parallel musical flow. Otherwise switching trains will be more like switching radio stations than adjusting the emotional state.