[Class]
midi-tempo-change

A MIDI tempo change event.

midi-tempo-change supports the following slot initializations:

:time number
The start time of the object.
:usecs integer
Number of microseconds (usecs) per MIDI quarter note. See Example 2 for how to convert musical tempo to usecs.

Examples:

Example 1. The midi-tempo-change event. 

;;; tempo 120 quarters per minute
(new midi-tempo-change :time 0 :usecs 500000)

;;; tempo 90 quarters per minute
(new midi-tempo-change :time 0 :usecs 666667)

Example 2. Converting quarter notes per minute to usecs. 

(define (qpm->usecs bpm )
  (inexact->exact (round (* (/ 60 bpm) 1000000))))

(define (accel num tempo1 tempo2)
  ;; accelerate in num quarters from tempo1 to tempo2
  (process for i below num
           for r = (interp i 0 tempo1 (- num 1) tempo2)
           output (new midi-tempo-change :time (now)
                       :usecs (qpm->usecs r))
           output (new midi :time (now)
                       :duration .5 
                       :keynum (between 60 72))
           wait 1))

(events (accel 20 60 240) "test.mid")
⇒ "test.mid"

See also: