Monday, 4 February 2008

writing up a term's worth of work

Not the most normal first post for a blog I guess... but the main purpose of this blog existing is to help me collect my thoughts together in my doctoral research. With that in mind then, the next few posts in this blog are going to help me collect together my thoughts on a project I'm working on.

I'm keeping details of the work I'm doing in a separate diary, but (stupidly) haven't kept much record of the papers I read in the build-up to carrying out this project.

So - I'm going to write short summaries of some papers relating to this project, that will include my reactions to them and how the work in the paper is relevant to my project.

A good starting point for this is to define the problem I am currently working on. Let's see if I can describe it (hopefully this will form part of the introduction for the paper I am writing):

Musical pieces can be made up of several melodic lines interwoven together. These melodic lines are commonly known as voices, although they are not used only in vocal music but are also to be found in music written for instruments. What is important about the voices is that each voice can be considered as a standalone melodic pattern, complete and interesting in its own right. Several related voices, combined together to form one piece of polyphonic music, can generate additional harmonic qualities to enhance the voices.

Fugues are a perfect example of this compositional technique in action, being constructed solely of a number of different melodic voices. J. S. Bach was a fundamentally important composer in the history of fugue composition; in particular his highly influential work The Well-Tempered Clavier comprises 48 fugues. Bach wrote two fugues in every key, to illustrate the full potential of each harmonic key in comparison to each other.

In analysis on Bach fugues, the musicologist identifies each individual voice first; this enables them to perform more advanced analysis on the melodic content such as the re-use of a melodic pattern in different voices. The musical score usually gives the musicologist much help in identifying each voice, as each voice is notated slightly differently (the direction of the note stems indicates which voice each note belongs to).

Identifying each voice would be a considerably harder task, however, if the notational clues were removed. The musicologist would rely on much information within the piece, such as the pitch of the notes and the rhythmical structure. They would use this information in conjunction with their knowledge of how Bach typically structured fugal voices.

Can a computer learn how to perform the same task of extracting the constituent voices from a Bach fugue? I suggest that, given minimal (if any) human assistance and a training set of fugues with the fugal voices already identified, patterns of vocal movement can be identified and learnt. Such patterns can then be used as background knowledge of Bach's fugal voice-writing, to assist the computer in identifying individual voices in a previously unseen Bach fugue.
I'm sure that introduction to the problem area will get extensively re-written but currently I am at the stage of a first draft of a paper describing my solution to this task.

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