[Coco] music synth on speed

[Kevin Diggs]

Hi,

	If you want to run your synth at high speed:

<div class="moz-text-flowed" style="font-family: 
-moz-fixed">ORCHESTRA-90/CC WITH FAST COCO

By Bryan Eggers
Software Affair, Ltd.


YOU MAY BE ABLE TO RUN YOUR
COCO AT DOUBLE-SPEED TO ENHANCE
THE MUSIC QUALITY OF TANDY'S
ORCHESTRA-90/CC MUSIC SYSTEM -
BY USING AN UNDOCUMENTED
COMMAND IN THE CARTRIDGE!


IMPORTANT:

READ THIS ARTICLE COMPLETELY
FIRST!!!


The quality of sound produced
by any digital synthesizer is
directly proportional to its
sampling rate. The sampling
rate is primarily determined by
the efficiency and clock rate
of the host processor. Tandy's
ORCHESTRA-90/CC is no exception
to this rule. The 6809 used in
the Color Computer is certainly
one of the best processors that
could ever be used for music
synthesis, and we are very
happy with the sound produced
by the ORCH-90/CC when used on
a standard Color Computer at
normal speed.

Many Color Computers will run
at TWICE the normal speed, and
will do so without any hardware
modifications whatsoever. If
you are lucky enough to have
one of these computers, you can
enable your CoCo's faster clock
by using a special undocumented
command from within ORCH-90/CC.
This will make a significant
improvement in the overall
sound quality produced by the
ORCH-90/CC music synthesizer!

Using the faster speed lets you
play in 4- and 5-part harmony
and almost never worry about
aliasing. The ORCH-90/CC will
automatically make all tempo
and transposition adjustments,
resulting in a better sound
quality improved by the higher
sampling rate. You can play
higher and cleaner notes, and
define more partial harmonics
than were possible running at
normal speed. Best of all, it
won't cost you a cent to try
it!


   ****** IMPORTANT ******

Tandy designed the Color
Computer to operate at NORMAL
speed, not at double speed!

Tandy does not in any way,
shape or form, support,
warranty or otherwise guarantee
that the Color Computer will
run at any faster speed!!
Therefore, if your system does
not run reliably at double
speed, you CANNOT blame Tandy!
Do it at your own risk. You are
attempting to run your system
outside of published specs, so
keep that in mind. If your
system does not run at
double-speed, it does NOT mean
that you have a defective
computer or a defective
ORCH-90/CC cartridge!!!


ENABLING THE FASTER CLOCK

In an effort to make sure that
no one would accidentally
invoke the undocumented
command, and perhaps lock-up
their system and get totally
confused, we devised a special
keystroke sequence that must be
followed exactly.


STEP 1

When you first plug in
ORCH-90/CC and turn on the
computer, you'll see the
copyright and licensing
information. Before pressing
any other keys, hold down the
<SHIFT> key and press <ENTER>
once. The demo tune is
displayed. Other than that, it
didn't look like the command
did anything special, did it?
Well, that keystroke toggles an
internal switch that now gives
you the OPTION of using the
speed-up command along with
certain other commands. In
other words, by configuring
ORCH-90/CC with this initial
keystroke of <SHIFT><ENTER>,
you're telling the system that
you MIGHT use the special high
speed enable command. But,
unless you press these keys
when you first turn on the
system, you will not be able to
use the speed-up command at
all. We expect that this
special way of configuring the
system will prevent any
accidents.

The <RESET> button has no
effect whatsoever on this
feature. If you press <RESET>
later to break a printer
lockup, for example, you'll
still be able to use the
speed-up command. By the way,
you can press <RESET> at any
time without losing the current
music file in ORCH-90/CC's
buffer.


STEP 2

At this point, all commands
still work normally. Keep in
mind that you only need the
fast clock during the actual
playing of a song. The normal
clock rate provides plenty of
speed for all other features.

The commands that we let you
enhance, therefore, are the
GET, PLAY, and MULTI commands,
since they are all used to play
music. These commands are
normally followed <ENTER> to
execute the command. An
optional string of filenames
may also follow these commands,
also eventually terminated by
<ENTER>. All this is normal
operation so far.

Everything works normally until
you use <SHIFT><ENTER> instead
of <ENTER> to terminate these
commands! Using <SHIFT><ENTER>
instead of <ENTER> enables the
fast clock mode and executes
the desired command
simultaneously!

For example, suppose you wanted
to play the three files BACH,
BACH2, and XYZ. Normally, you
would type:

G BACH BACH2 XYZ <ENTER>

But, to play the songs with the
faster clock, you'd type:

G BACH BACH2 XYZ <SHIFT><ENTER>

The system would load and score
each tune automatically, then
just as it begins playing the
tune, ORCH-90/CC switches your
system's clock to high speed.
The fast clock is turned off at
the end of the tune, and the
system loads the next tune,
plays it with the fast clock,
etc.

As another example, you could
type:

M * <SHIFT><ENTER>

This MULTI command, combined
with the "*" wildcard
character, will automatically
play all songs on the disk,
switching to the fast clock
while playing each!

You could still execute any
of these commands with <ENTER>
to play the tunes normally.

Same is true of the PLAY
command (P). Just use:

P <ENTER> to play the current
tune normally, or:

P <SHIFT><ENTER> to play the
current tune using the fast
clock.


IF IT WORKS...

If your system can run reliably
at double speed, the screen
display will temporarily blank
out while the music file is
playing, sounding even better
than before. All available
processor time is now used
for synthesis - no time for
screen displays. This is a
side-effect of the way the CoCo
hardware handles the speed-up,
not a problem with the
ORCH-90/CC cartridge. Sorta
makes an interesting light
show, though!

After the music finishes
playing, the speed is switched
back to normal, the screen
image is restored, and the
music file has not been lost.


IF IT DOESN'T WORK...

If your system can't handle the
faster speed, the results can
be unpredictable, but usually
one of the following will
happen:

(1) The system locks up.

(2) Screen fills with garbage.

(3) The music plays OK, but the
file in memory is now full of
garbage when you return to the
editor. You can still use your
CoCo to play music with the
fast clock, even with this
problem, but if you are editing
or creating files, remember to
save your music file to disk
BEFORE playing it!). You'll
have to test your system
thoroughly to make sure that
the music file itself remains
intact.


If your system doesn't run
reliably at high speed, it may
be possible to modify it to do
so, but that is a project for a
real hardware expert. You might
check with your local user
group for such a person. Also,
check the ads in the CoCo
magazines. You might find
someone who can supply or
install a modification for you.
Let us know what you find out
and we'll post it in the
database! If you really
like music synthesis, any
effort it takes to get your
system running at double speed
will be worth it in terms of
the enhanced sound quality.

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