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Improving Recording Timing Nuances
==================================
This chart converts Tempos (BPMs) from 40-330 into Millisecond delays for 1
clock tick PPQN settings from 96-1024. It is useful for maximizing your
sequencers resolution PPQN settings for obtaining the best "nuance" recording
within MIDI's bandwith limitation limit, i.e. one MIDI byte takes a minimum of
(10 bits divided by 31,250 bits per second rate) .32 milliseconds to be sent.
It can be used by the more versatile computer sequencers but also for hardware
fixed PPQN sequencers such as the XPs.
Because the XP-50 and XP-80 internal sequencer resolutions are fixed at 96
PPQN, a way to get around the recording bandwith for better live "timing
nuance" recording, is to "manipulate" the tempo to "virtually" improve the
MIDI data's timing accurancy. In other words, to obtain notably improved
sequencer recording functionality at slow tempos especially, use a multiple of
the "actual" tempo to record with thereby perceptably minimizing the delay
times of note events.
For example, if recording a piece whose actual tempo is 60 BPM, to obtain
better recording PPQN resolution, use a "virtual" tempo of perhaps 240 to
minimize the delay of 1 PPQN from 10.4178ms to 2.604ms. I recommend always
trying to, since the ear can perceive timing fluctuations as small as from
5-10ms, use the chart to "compensate" for better PPQN resolutions based on
tempo.
Time for PPQNs with 1 PPQN Delay Time in Milleseconds (ms)
Tempo Beat/Sec 96 120 192 240 384 480 768 1024
40 1.500000 15.625 12.500 7.813 6.250 3.906 3.125 1.953 1.465
50 1.200000 12.500 10.000 6.250 5.000 3.125 2.500 1.563 1.172
60 1.000000 10.417 8.333 5.208 4.167 2.604 2.083 1.302 0.977
70 0.857143 8.929 7.143 4.464 3.571 2.232 1.786 1.116 0.837
80 0.750000 7.813 6.250 3.906 3.125 1.953 1.563 0.977 0.732
90 0.666667 6.944 5.556 3.472 2.778 1.736 1.389 0.868 0.651
100 0.600000 6.250 5.000 3.125 2.500 1.563 1.250 0.781 0.586
110 0.545455 5.682 4.545 2.841 2.273 1.420 1.136 0.710 0.533
120 0.500000 5.208 4.167 2.604 2.083 1.302 1.042 0.651 0.488
130 0.461538 4.808 3.846 2.404 1.923 1.202 0.962 0.601 0.451
140 0.428571 4.464 3.571 2.232 1.786 1.116 0.893 0.558 0.419
150 0.400000 4.167 3.333 2.083 1.667 1.042 0.833 0.521 0.391
160 0.375000 3.906 3.125 1.953 1.563 0.977 0.781 0.488 0.366
170 0.352941 3.676 2.941 1.838 1.471 0.919 0.735 0.460 0.345
180 0.333333 3.472 2.778 1.736 1.389 0.868 0.694 0.434 0.326
190 0.315789 3.289 2.632 1.645 1.316 0.822 0.658 0.411 0.308
200 0.300000 3.125 2.500 1.563 1.250 0.781 0.625 0.391 0.293
210 0.285714 2.976 2.381 1.488 1.190 0.744 0.595 0.372 0.279
220 0.272727 2.841 2.273 1.420 1.136 0.710 0.568 0.355 0.266
230 0.260870 2.717 2.174 1.359 1.087 0.679 0.543 0.340 0.255
240 0.250000 2.604 2.083 1.302 1.042 0.651 0.521 0.326 0.244
250 0.240000 2.500 2.000 1.250 1.000 0.625 0.500 0.313 0.234
260 0.230769 2.404 1.923 1.202 0.962 0.601 0.481 0.300 0.225
270 0.222222 2.315 1.852 1.157 0.926 0.579 0.463 0.289 0.217
280 0.214286 2.232 1.786 1.116 0.893 0.558 0.446 0.279 0.209
290 0.206897 2.155 1.724 1.078 0.862 0.539 0.431 0.269 0.202
300 0.200000 2.083 1.667 1.042 0.833 0.521 0.417 0.260 0.195
210 0.285714 2.976 2.381 1.488 1.190 0.744 0.595 0.372 0.279
320 0.187500 1.953 1.563 0.977 0.781 0.488 0.391 0.244 0.183
330 0.181818 1.894 1.515 0.947 0.758 0.473 0.379 0.237 0.178
Because the MIDI bandwith is limited to .33ms for a one byte message, but more
practically is limited to .96ms for note on messages without "intermittent"
running status, all PPQNs for tempos whose 1 PPQN is less that .33ms are NOT
possible and less than .96ms are NOT practical. Also, for "realistic"
recording, quintuplet factorable PPQNs such as 120, 240, 240, should IMHO be
avoided to prevent "false" quantization errors which I don't believe human
performances ever use! Multiples of 2 and 3 are the most "natural" and basic
prime quantizations.
Due consideration for maximum polyphonic delays should be made. Consider the
following delays REQUIRED for various simultaneous polyphony between clock
ticks:
Polyphony Notes at .96ms per NoteOn
========= ==========================
1 .96 ms
4 3.84 ms
8 7.68 ms
16 15.36 ms
32 30.72 ms
64 61.44 ms
More expressive controller and note recordings when adequate but practical
PPQNs are used to increase the efficiency of use of the sequencer's PPQN
resolution. Using for example a PPQN of 1024 at a tempo of 330 BPM causes
unnecessary CPU overheard and unrealizeable for MIDI's bandwith, since the 1
PPQN resolution is .178ms which is less than the .33ms that MIDI supports for
transmission/reception. On the otherhand, using a PPQN of 96 for a tempo of 40
BPM prevents recording/sending of any data whose timing is less than the 1
PPQN resolution of 15.625ms! Controller events especially can "suffer",
besides NoteOn event start/end times, from their recording/playback "nuance"
expressiveness.
Benjamin Tubb
[email protected]
http://www.cybertron.com/~brtubb
