Electrifying Duets
Mathematician Strives to Teach
PCs to Play Accompaniment
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By Paul Eng


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Oct. 4 - Could a computer ever
play music as well as a human
musician? 

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Some would argue that
computers already far
surpass any human
performer when it comes to
producing pristine tunes.
Music described in the
absolute digital code of ones and zeros
guarantees that a computer will play a
particular score the same way every
time. 

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But for Christopher Raphael, an
accomplished oboist, such an
unyielding musical performer would
hardly be an ideal partner for a human
musician to practice and possibly
perform with. The human player would
always have to conform to the
computer's pace of performance, for
example, and thus stifling the
individual's musical interpretation.

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So Raphael, a professor in the
department of mathematics and
statistics at the University of
Massachusetts at Amherst, has been
working on a software program that
would essentially give computers
human-like flexibility when it comes to
playing alongside flesh-and-blood
performers. 

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Listen, Analyze, Predict, and Play

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His software, Music Plus One, is
composed of over 40,000 lines of
complex computer code developed over ten years of research.
And how it works is based on how a real musician thinks and
processes audio information.

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First, data that describes the musical score to be played by the
human and the accompaniment part to be played by the
computer is keyed into the machine. In other words, the
computer is programmed with the digital equivalent of sheet
music which outlines every note of a musical performance.
 As the human instrumentalist plays his part, the computer
picks up the sounds via a microphone. Then by using
processing techniques similar to those used to recognize
speech, the computer analyzes what it "hears," and determines
what notes have been played and when they were played. 

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After several practice sessions, the computer develops an idea
of how a person plays that particular piece of music. What's
more, artificial intelligence algorithms in the Music Plus One
software allows the computer to "predict" how that performer
will play any particular note at any given point in the piece. In
turn, the computer can then anticipate how it needs to play its
corresponding musical part.

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Real-Time, Real Easy

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Raphael says the predictive capability of Music Plus One is
what sets his approach from other accompaniment programs
out there. 

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"If you're going to synchronize playing with another musician,
you just can't listen and react," says Raphael. "You need to do
what humans do: Take information about what you heard in
the past and predict what you need to do in the future."

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And Raphael says the software can do all of these tasks in "real
time." In other words, the program is listening, analyzing,
predicting and playing its part all in the same instant the
human instrumentalist is performing.

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What's more, Raphael says the Music Plus One software
doesn't require heavy-duty computer systems. He claims to run
the program, whimsically named in relation to the old Music
Minus One accompaniment records he use to practice with, on
a plain four-year old laptop with a standard Pentium-class
microprocessor. 

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Roger Dannenberg, a research computer scientist at Carnegie
Mellon University in Pitsburgh, Penn., has seen Raphael's work
at a recent gathering of the Acoustical Society of America and
is impressed.

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"Chris' work is some of the more advanced in terms of
developing performance systems," says Dannenberg who has
done similar research work several years ago and now holds
several patents in related music systems. "His system works
and I find it striking how it works so well."

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Is It Live Or Is It...?

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Raphael says that for now, Music Plus One remains a beloved
research project. "My main purpose is to see how far I can go
with this," he says. "My belief is that it can go a lot further." 

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How much further? 

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According to Raphael's research paper, the ultimate milestone
for Music Plus One would be to "pass the musical equivalent of
the Turing Test." In other words, could the software be refined
to such a degree that it can fool the listener into believing it's a
human and not a machine performing alongside a live
performer?

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To hear examples of Music Plus One in action, Raphael has
samples on his Web site:
http://fafner.math.umass.edu/music_plus_one.

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But in addition to working toward that goal, Raphael says it's
possible a version of Music Plus One could become available
for sale to musicians - some day. "I've worked very hard on this
and would like the world to use what I build," he says.

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For now, however, he hasn't broached any software companies
to convert his research into a commercial product.