Re: Rhythm

[Mark DeWitt <dewitt@xxxxxxxxxxxxxxxxxxxxx>]

Bill Hartmann writes:

>Dear List,

>This is a question about the ability to perceive irregularity in
>rhythm. It comes from Boogie Bob, Lansing's foremost rhythm and blues
>artist.

Most of the answers to the questions below have been of the "it depends"
variety, but so far no one has mentioned that cultural expectations for
what the music should sound like have a role to play.

Since the question comes from an R&B musician, it would make sense to look
at studies that have been done on the concept of "swing" in jazz, in
which the question is less of inter-onset intervals played by a single
musician than it is, how do all of the parts (bass, drums, piano, soloists)
fit together?  Ethnomusicologist Charles Keil has dubbed the term,
"participatory discrepancies," to cover the kinds of real-time rhythmic
and metrical negotiations that musicians do in an ensemble.  The Winter
1995 issue of the journal *Ethnomusicology* was devoted to this subject,
including two measurement studies (Vol. 39, No. 1).  Jeff Bilmes wrote
a masters' thesis on a related topic at the MIT Media Lab in the early
1990s, and Desain & Honing in the Netherlands have also been working
on expressive timing issues.

>
>        What is the JND for perceiving an unequal division of a beat into
>        two notes?
>

I wonder how Boogie Bob worded the question.  In a musical
situation such as he would find himself in, one part would not be
heard by itself.  How many of the studies cited by the list thus
far used a multi-part stimulus, such as an isochronous beat track as
a ground against which to judge the rhythmic figure?  What then happens
when the ground is de-isochronized, such as record producers do in the
studio with drum machines by adding a "feel formula" (Progler 1995:23)?

>        A quarter note beat could be divided into two eighth notes.
>        Theoretically, that would be a 50-50 division.
>
>        It could be divided into a dotted quarter and a sixteenth.
>        That would be a 75-25 division, clearly different from 50-50.
>
>        Can you distinguish between 75-25 and 67-33? How about 75-25
>        vs 70-30?

In jazz and pop music, one interesting "emic" boundary would be the
one between what is judged to be even versus long-short, e.g., Latin vs.
swing rhythm in jazz.  50-50 is even, but what about 60-40?  Also,
two performances could be judged to use even eighth notes, yet one
judged to be square and one to swing, which I suppose is the difference
between categorization and discrimination.

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

David Wessel would be one to ask on this.  If I recall a conversation
correctly, he did some work at IRCAM in the 1970s that showed faster tempos
to create a tendency to more even beat subdivisions, regardless of the
intention that might be represented by notation.  Progler's measurements
of one drummer's short notes in a long short pattern bear this out.  Tempo
is in beats per minute (bpm):

Tempo   Short note duration in a long-short pattern
-----   -------------------------------------------
 60 bpm 20% of beat length
120     25%
240     33%

Music notation in jazz has never settled on how to handle "swing eighths;"
it is not uncommon for an editor to notate almost everything in straight
eighth notes and simply note "Latin" or "swing" at the top of the score.

>Because this is a question about rhythm and not about the perception of tone
>duration, there needs to be a context. Probably it's best to think of a
>regular and indefinite repetition of the two-note sequence in question.
>That establishes the tempo and context.

>Anybody out there with information on this subject?

>Next: how about the ability to reliably PRODUCE such a division?

Progler reports that one musician "hadn't always played what he thought he
had," but cites experiments by Reinholdsson that indicate players can
control what they do in relation to a given beat.  If what you're talking
about, though, is the rhythmic equivalent of microtonal composition, I'd
say no, you may be able to devise a notation that differentiates between
75-25 and 70-30, but good luck training performers to play it.

Mark DeWitt


References

Bilmes, Jeffrey A. 1993. *Timing Is of the Essence: Perceptual and
Computational Techniques for Representing, Learning, and Reproducing
Expressive Timing in Percussive Rhythm.* [M.S. thesis].  Cambridge,
MA: Massachusetts Institute of Technology.

Desain, Peter and Henkjan Honing. 1992.  *Music, Mind, and Machine:
Studies in Computer Music, Music Cognition and Artificial
Intelligence*.  Amsterdam: Thesis Publishers, P.O. Box 14791, 1001 LG
Amsterdam, The Netherlands.

Proegler, J. A.  1995.  "Searching for Swing: Participatory
Discrepancies in the Jazz Rhythm Section."  *Ethnomusicology*
39/1:21-54.

Reinholdsson, Peter. 1987.  "Approaching Jazz Performances
Empirically: Some Reflections on Methods and Problems."  In *Action and
Perception in Rhythm and Music*, ed. Alf Gabrielsson, 81-103.  Royal
Swedish Academy of Music No. 55.  Stockholm: Royal Swedish Academy of
Music.