Phil Taylor posted the following & I see no problem with his reasoning.

>Q:300 means 300 default notes/min. Tune is 32 bars long, each bar
>containing 4 default notes, so 128 defnotes in all. It should
>therefore take 128 * 60 / 300 = 25.6 seconds to play through once.

Below is the tune I want to play back. It plays at the desired speed
when pasted into ABC2Win. The program automatically selects 1/8 as the
default note length for playback (L:1/8) Abcedit seems to use 1/4 note
as the default (M:2/4) I can force the playback by editing Q:300
(Q:1/8=300)
This is only way I know that playback will work in each of my
applications.

X: 041262
T: Dan O'Connell's
S: "Johnny O'Leary of Sliabh Luachra" (#221)
Z: B.Black
L: 1/8
M: 2/4
R: polka
Q: 300
K: D
F2 ED|dc/d/ ed|cA AF|G2 GA/G/|
FD FE/D/|dc/d/ ed|cA BG/B/|A2 A2 :|
af/a/ ge|fd e/f/e/d/|c>d ef|g2 fg|
a>f g>e|fd e/f/e/d/|cA BG|A2 A2 :|