In order to notate 60 BPM where the actual duration of the sounded pitch lasts only 1/2 second, you would notate uses pairs of eighth notes and eight rests.
X: 1
T: 60 BPM Example #1
T: Sounding durations = 1/2 sec.
M: 4/4
K: none
Q: 1/4=60
!tenuto!B z !tenuto!B z !tenuto!B z !tenuto!B z |
The lines above the notes are "tenuto" marks, which mean to be sure to hold the note for its full length.
This could also be notated using staccato markings on quarter notes. A common interpretation for staccato notes is that they take up half the notated length.
X: 1
T: 60 BPM Example #2
T: Sounding durations = 1/2 sec.
M: 4/4
K: none
Q: 1/4=60
L: 1/4
.B .B .B .B |
My personal preference would be the eighth-note/eighth-rest notation. I find it more precise, especially since I don't adhere to the "staccato = 1/2 length" convention.
The BPM designation and the time signature "beat note" need not be the same. Tempi can be given in terms of BPM (corresponding to the time signature's "beat note") or in terms of a note type.
For example, in 6/8 time, it's common to give the speed in dotted quarter notes, even though the time signature indicates eighth notes as the "beat note". 3/4 time, when the speed is fast, is often given in terms of dotted half notes per minute. 2/2 time is sometimes given in quarter notes or whole notes.
I think the confusion is that there are two somewhat independent notations. 1/4 = 60 means "there are 60 quarter notes per minute." dotted-quarter = 120 means "there are 120 dotted quarter notes per minute." These notations can be independent of the time signature — or rather can be adjusted to the time signature.
BPM is specific to the designated "beat note". So, in 3/4 time, the following notations would all result in exactly the same overall speed:
- dotted half-note = 40
- quarter-note = 120
- 120 BPM