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Re: Rhythm

> This is a question about the ability to perceive irregularity in
> rhythm. It comes from Boogie Bob, Lansing's foremost rhythm and blues
> artist.
> What is the JND for perceiving an unequal division of a beat into
> two notes?

Another relevant article by Repp is in the latest issue of Musicae
Scientiae (vol. 1 no 2, fall 1997), "Expressive Timing in a Debussy
Prelude".  Eric Clarke ("Levels of Structure", Contemporary Music Review
1987) cites Kristofferson's estimate of 8% but suggests that "we can
expect them to become sharper with appropriate context" (p.224); David
Epstein (Beyond Orpheus, 1979; see also Shaping Time, 1995) also talks
about this issue and proposes a large range, quoting Getty and Mach
estimates of 5% to 33% (!) depending on specific durations: 33% was for
15-sec. durations. Hirsh et al ("Studies in Auditory Timing", Perception
& Pyschophysics 47 (1990) suggest 5%-10%.

The problem is certainly contextual, as it seems likely that two
different types of information are gleaned by the listener from the
rhythm: the basic rhythmic configuration (dotted quarter followed by
sixteenth, for ex.), and the modification of that for expressive reasons
and/or indications of the motive's position within the bar, phrase,
etc.  (see for ex. Eric Clarke's research about the slowing down of the
pulse towards the "group boundary", op.cit. 225).

Another contextual influence would be register, and (to a lesser
extent?) timbre, as the tracking would be affected if there exists a
wide registral &/or timbral distance between 2 sequential notes (though
this effect would probably diminish with increased repetition).

> Presumably the answer depends somehow on the tempo. How?

My own research, which is not based directly on laboratory research but
rather on analysis & listening, accompanied by a study of the current
research in rhythmic perception (and info. theory, etc.), indicates that
the perception of periodicities is extremely tempo-related -- i.e. that
a periodic event which happens roughly faster than about 0.50 sec.
(120/min) is no longer perceived as a pulse, no matter what the score
might say, and likewise that slower than about 1.50 sec. (40/min) will
be interpreted as a pulse-grouping.  This seems to relate to simple
physiological factors with leg and arm movements acting as a reference.

In other words, I agree with Steve Boker:
> As is often the case, the answer to your question seems to be "it depends".

Dr. Rosemary Mountain
Communication & Art
Universidade de Aveiro
3810 Aveiro - Portugal

e-mail: mountain@ua.pt

Fax:    +351-34-370868