Re: A Couple of Midi Tempo and TimeSig Questions
Re: A Couple of Midi Tempo and TimeSig Questions
- Subject: Re: A Couple of Midi Tempo and TimeSig Questions
- From: Doug Wyatt <email@hidden>
- Date: Thu, 15 Apr 2004 17:57:17 -0700
On Apr 15, 2004, at 11:06, William Stewart wrote:
On 14/04/2004, at 8:02 PM, Brian Willoughby wrote:
Peter,
I believe that the theoretical maximum Tempo would be 60,000,000 BPM.
The
Standard MIDI File encodes a Tempo Meta Event in microseconds per
quarter-note,
as a 24-bit integer. The lowest Tempo would be 0.27962 BPM. However,
the
Tempo is also effectively modified by the Time Signature Meta Event,
which
includes a byte for "Clocks Per Metronome Click" [0-255] and "Notated
32nd-notes Per MIDI Quarter-Note" [0-255]. The math for that is left
to the
reader. I couldn't find the SMF spec on hand, and I cannot remember
if the
usec count is allowed to range from 1 to 16,777,216 as allowed by the
bits
allocated.
No. Tempo events are not modified by Time Sig events. Time Sig events
are purely informational, and have no baring on Tempo.
The reason for this is that MIDI File tempos are described in
microseconds per quarter note. MusicPlayer's "beats," as in MIDI, are
actually quarter notes. So the denominator of the time signature is
indeed not necessary for interpreting tempo events.
Doug
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