In any type of step-entry MIDI file, tempo is an important
contributor to the overall effect and I don't just mean in the obvious
sense of general speed of a work or section of a work. I mean rather
that, just as the loudness of notes can have different degrees and
shadings, so can tempo.
In many cases a single tempo can last through many measures
but often notes may be drawn out more or less subtly as in the classic
"tempo rubato" ("robbed time") where more time can be given in one
place and then made up for by accelerating (the "payback").
In a piano piece such as a Chopin Nocturne or even a Mozart
slow movement, for example, this can mean that the right hand goes
behind or ahead while the left hand keeps strict time. The results of
the hands not being together sounds sloppy to modern ears, so the left
hand tempo is now generally changed to accommodate the right.
But, in fact, I have used the classic technique in a few
spots (rarely in the Elgar Violin Concerto where it might be expected)
such as at rehearsal number 79 in the slow movement of the Elgar Second
Symphony for the oboe solo where I probably inserted the notes in
realtime and then edited them. Here the high notes, mostly, and the
tenuto notes, even more, hold out. Then the rest goes faster to make up
the time so it finishes together with the other tracks which remain at
the stricter slow-march tempo. (Elgar marks the oboe solo "molto
rubato, quasi ad lib".) Also the violin solo near the end of the slow
movement of the Brahms First Symphony where I did something similar.
In the Overture "In the South" there was a problem with many
of the eighth notes especially those marked with tenutos. In order to
make sense, they needed to be slowed down in comparison to the rest of
the tempo but not to the point of distortion!
And here I'd like to make a few comments on tenuto. The
meaning of the term is like its English cognate "tenacious" ("sticking"
to the notes or, standard definition, holding them for their full
length.). Of course, it's often used on notes in a staccato passage
which are to be non-staccato and that is its most obvious meaning. But
aside from that, what does Elgar mean when he marks dashes above or
below the notes? Paradoxically, in practice, it seems to mean that the
notes should be not quite legato unless slurs are also present!
Mainly I think it often means to slow down slightly but make
the notes slightly detached. Sometimes it seems to mean a slight
fermata or sometimes just less phrased. And, at other times a very
slight accent is also implied. I would advise a sequencer to try to
perceive the real musical meaning and to be flexible about how it is
accomplished. I adopted a rather free tempo for the theme of the Enigma
Variations because of the tenuti and think, at least in that brief
instance, I was more expressive than, say, Adrian Boult who seems to
ignore many of these markings. (Elgar's own recording is, of course,
I've written at length about the sequencing of the Violin
Concerto cadenza and how an extra beat may be added if necessary and
the actual time adjusted with tempo when a long break is desired. But
in many works, shorter breaks are wanted, between sections for
instance. Here, I usually use the procedure of shortening the final
note or chord slightly before the break and again adjusting the tempo
to increase the break time, if desired. Not doing this can give an
effect similar to a run-on sentence in grammar. The tempo change can
increase the held time (as in a fermata) or break time or both,
depending on where and to what degree the slower tempo is inserted.