I have learned that MML (Music Macro Language) and our PLAY command comes from GW-Basic. Per the GW-Basic Users Manual (Quite a lot of the GWBasic documentation applies to EngineBASIC):
Note: any references to hardware limitations wont apply to our BASIC Engine. I have not tried all of these commands yet.
To play music by embedding a music macro language into the string data type.
PLAY string expression
The single-character commands in PLAY are as follows:
A-G [#,+,-] A-G are notes. # or + following a note produces a sharp; - produces a flat.
Any note followed by #,+, or - must refer to a black key on a piano.
L(n) - Sets the length of each note. L4 is a quarter note, L1 is a whole note, and so on. n
may be from 1 to 64.
Length may also follow the note to change the length for that note only. A16 is
equivalent to L16A.
MF - Music foreground. PLAY and SOUND statements are to run in foreground. That is,
each subsequent note or sound is not started until the previous note or sound is
finished. This is the initial default.
MB - Music background. PLAY and SOUND statements are to run in background. That
is, each note or sound is placed in a buffer allowing the BASIC program to
continue execution while music plays in the background. As many as 32 notes
(or rests) can be played in background at one time.
MN - Music normal. Each note plays seven-eighths of the time determined by L
ML - Music legato. Each note plays the full period set by L.
MS - Music staccato. Each note plays three-quarters of the time determined by L.
N(n) - Play note n. n may range from 0 to 84. In the 7 possible octaves, there are 84
notes. n set to 0 indicates a rest.
O(n) - Octave 0 sets the current octave. There are 7 octaves (0 through 6). Default is 4.
Middle C is at the beginning of octave 3.
P(n) - Pause. P may range from 1-64.
T(n) - Tempo. T sets the number of L4s in a minute. n may range from 32-255. Default
. (period) - A period after a note increases the playing time of the note by 3/2 times the
period determined by L (length of note) times T (tempo). Multiple periods can
appear after a note, and the playing time is scaled accordingly. For example, A.
will cause the note A to play one and half times the playing time determined by
L (length of the note) times T (the tempo); two periods placed after A (A..) will
cause the note to be played at 9/4 times its ascribed value; an A with three
periods (A...) at 27/8, etc.
Periods may also appear after a P (pause), and increase the pause length as
Xstring; Executes a substring, where string is a variable assigned to a string of PLAY
Because of the slow clock interrupt rate, some notes do not play at higher
tempos; for example, 1.64 at T255. These note/tempo combinations must be
determined through experimentation.
">n" - A greater-than symbol preceding the note n plays the note in the next higher
"<n" - A less-than symbol preceding the note n plays the note in the next lower octave.
Numeric arguments follow the same syntax described under the DRAW statement.
n as an argument can be a constant, or it can be a variable with = in front of it ( = variable ). A
semicolon is required after the variable and also after the variable in Xstring .