SamMaEl <rimsky@teleport.com> wrote:

>	"Higher" frequency, lower pitch. Just like when you pluck a
>string, then shorten the string by a half, the note will sound an octave
>higher. Or, so said Pythagoras. And just the same, cutting the
>frequency in half raises the pitch an octave. So, 880 Hz would be the A
>above middle C, and 440 Hz would be the A an octave higher than the 880 A.

Actually, Doubling the pitch raises the frequency one octave.  Under a
given tension and linear density, cutting the distance by one half will
double frequency.

Think of a guitarist.  The further up on the neck he/she plays
(ie--shortening the effective length of the vibrating string) the higher
the pitch.

For tension--think of tuning a stringed instrument.  Tightening the pegs
(more tension = higher pitch).

Similarly for the volume of a closed resonant structure--lownger is lower.
Think trombone.

And BTW A=440 Hz is the a above middle 'C' (second space on a treble clef).
A=880 lies on the first ledger line above the treble clef.

In terms of MIDI, Middle 'C' equates to note #60 (base-10).  As the MIDI
note increases (by integer), pitch increases one half step.  (61= C#, 62 =
D).  Going back to the guitar analogy, a half step is the musical distance
attained by going up/down one fret on a given string.  Or, on a piano, by
going to the next adjacent black or white key.


Most synthesizer manufacturers equate this with 'C3', the notable exception
being Yamaha, who calls Middle C 'C4'.  MIDI 'plays notes' with a series of
Channel Voice Messages.  A note is played by sending a 'note on' message
whose data flags indicate which MIDI channel (1-16) should play the note,
the pitch of the note, and the velocity (loudness of the note).  Duration
is not specified.

The note will continue to play until a 'Note Off' message comes along.
'Note Off', like Note On must specify MIDI channel and Note #.

If you've ever used a sequencing app, you've probablyu seen a command
called 'panic/all notes off', which when invoked seems to send a wall of
MIDI data out.  What i'ts doing is sending a MIDI Note Off message for each
possible note value on each MIDI channel.

End of today's tangental lecture on music technology.

Steve Revilak
revilak@umbsky.cc.umb.edu