Jos discussed time signatures with his usual
clarity and insight.  One point: you can actually
have as many quarter notes as you want in a
bar marked with (say) 4/4 time.  In fact, it has
become common practice from the 1970s onward
in serious modern music and in some prog rock
and progressive jazz to squeeze lots more 
quarter notes into a bar of 4/4 than a mere 4.
    How is this done?
    By using n-tuplets.
    Those of you with high-end modern music
scoring programs know that one of the more
intriguing features of these programs is the
facility to grab a set of notes with your mouse
and turn 'em into n-tuplets. For example,
you could enter 5 quarter notes into a bar
of 4/4 and grab 'em and use the various 
keystroke commands to make 'em into
a 5-tuplet.  In other words, "5 quarter
notes in the time of 4."
   Triplets are familiar to us all from as early
as the 14th century with well-known 
compositions like Tout Par Compas by
Baud Cordier and Fumer Fumeaux by
Petrus de Goldescalc. Triplets soon
became a staple of Western music,
used by such notables as Monteverdi,
Bach, Beethoven, and Gershwin. By
the 20th century, however, n-tuplets
had expanded far beyond triplets into
4-tuplets (4 in the time of 3), 5-tuplets
(5 in teh time of 4), 6-tuplets (6 in the
time of 4, typically), 7-tuplets (7 in the
time of 6), and so on. 
    The real metric complexities arise when
you start embedding tuplets. For example,
you could embed triplet eighth notes into
5-tuplet quarter notes.  Meaning: 5 quarter
notes in the time of 4, but one of those 5
quarter notes gets borken into 3 eighth
notes.
    This kind of embedded tuplet metrical
complexity can be heard in jazz in Dave
Brubeck's spectacular "Unsquare Dance,"
also in some of the solo lines of John
Coltrane and Charlie Parker. In classical
20th century music, Bartok and Stravinsky
made extensive use of embedded n-tuplets.
However, the real explosion in the use of
embedded n-tuplets occurred after 1970.
Steve Reich makes extravagant use of 
embedded n-tuplets in such pieces as 
"New York Counterpoint" and "Four Organs,"
while Michael Gordon's "Yo, Shakespeare!"
and a number of pieces by Julia Wolfe
(both of Bang On A Can fame) employ 
n-tuplets in almost all their recent
compositions. A number of modern
Netherlands composers also make use
of embedded tuplets. Perhaps the king
of embedded tuplets in modern music
is Brian Ferneyhough, whose music 
remains as unplayable as it is laughable
to read in score. I handed a friend a page
from Ferneyhough's Ciaconna for solo
violin and he thought it was a joke. Alas,
no. Just embedded n-tuplets carried
way, wayyyy too far (11-tuplets inside
17-tuplets inside 19-tuplets inside 13-tuplets
inside 7-tuplets inside...  You get the idea.)
    Arguably the great sea-change in post
WW II music involves the use of successively
more copmlex metrical relationships. 
    How does any of this relate to the Atari
ST and MIDI?
    It turns out Dr.. T's KCS allows the composer
to specify variable fractional tempo relationships
of one sequence to another.  This is effectively
the same thing as n-tuplets.  To give one example,
5 in the time of 4 is equivalent to playing a sequence
of 5 quarter notes with a tempo of 100% against
4 quarter notes with a tempo of 80%. KCS makes
much more complex tempo relationships possible,
and also includes the option to change the tempo
of the entire playback in real time by grabbing
the tempo slider.
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--mclaren