Richard Bettis
The Music 5000 environment provides 14 standard waveforms -
Bright, Broad, Clear, and so on. These are defined during the start-up of the
system. Unlike its predecessor (the Music 500) there is no facility to alter
these waveforms, or to change their names.
In some ways this is an advantage - using the Music 5000
approach is certainly much simpler, and the pre-defined waveforms cover many of
the sound types that one might want to produce.
In some circumstances, however, it would be nice to have
some wave definition abilities. For example, I really like a good strong square
wave sound, which 'Hollow' just doesn't quite produce.
In AMPLINEX 009, Ian Guinan described the relationship
between the Music 500 and 5000 waveforms, and demonstrated a method for using
the Music 500 waveforms on the Music 5000. The big disadvantage of this method
is that you need to run the Music 500 software to set up the waves. (I hardly remember
how to do it, and others won't have a copy).
I have therefore written the U.Wave program, which allows
any (or all) of the Music 5000 waveforms to be redefined.
Using U.Wave
1) The main screen
When U.Wave is RUN it gives a mode 4 screen divided into
three windows.
At the top is a graph in which a waveform can be displayed.
Below that, to the right, is a chart of harmonic levels for a waveform. These
are similar to the charts on pages 127-129 of the Music 5000 User Guide.
The third window is for AMPLE, and serves to confine user
activity to one area of the screen. It is in this window that you control the
actions of U.Wave.
2) Seeing it work
There are 4 waveforms built into the program. In each case
they replace the 'Hollow' waveform with the new one. An instrument definition (imaginatively
called 'ins') puts the wave to work.
The 4 waveforms are: Square, Saw, Pulse and Hwave. Entering
the wave name causes the whole redefinition process to be carried out.
3) Doing it yourself
A waveform definition consists of 128 points which describe
one cycle of the wave. Each point can have a value between -127 and 127.
For example, the Square wave has points 1 to 64 all at 127,
and points 65 to 128 all at -127.
As an alternative, a wave can be described using the
relative strengths of the first sixteen harmonics. Each harmonic strength can
be at any value from 0 to 255.
For example, a pure sine wave would have a first harmonic of
strength 255, and all the others at 0.
The waveform defining words are compatible with those on the
Music 500 and are all defined in upper case. This means that Music 500 wave definitions
can be imported although some preparation may be needed to cope with other
AMPLE BCE to Nucleus discrepancies (such as RAND? versus RAND).
4) Wave definition vocabulary
The syntax of each word is shown below using lower case
letters to indicate numerical values. There is also a short description of its
use.
WZERO initialises the
wave and harmonic buffers,
setting all values to 0
x WMOD specifies which
wave is to be changed (see table 1)
x = 0 to 13
vv nn WG! sets the value
of wave point nn to vv
nn = 1 to 128
vv = -127 to 127
nn WG? puts the value
of wave point nn on to the stack
nn = 1 to 128
(e.g. 100 WG? NOUT will print
the value of point 100)
WGC moves the
waveform from the computer to the synthesiser unit
Once this is done the new waveform can be used
ss hh WH! sets the
strength of harmonic hh to spreadsheet
hh = 1 to 16
ss = 0 to 255
WHG This makes a
waveform from the harmonics specified by WH!
This must be done prior to a
WGC command to put the waveform
into the synthesiser unit.
5) Other U.Wave commands
There are some other commands in the U.Wave program which
are for interactive use.
wdraw displays the
current waveform
Any waveform created by a user
word or by direct entry of
wave change commands in the AMPLE window can
be seen using
this method.
edit loads the
Notepad editor so that the predefined waveforms
may be examined and altered.
(In mode 4 on a standard BBC
Model B there is so little room left that many
extra
waveforms are impossible)
graph gets back to the
mode 4 graphics screen,
QUITting and MDELETEing the
editor.
dump spools all the
words needed for wave manipulation out to a
file called E.WaveUse. This can then be
*EXECed into other
programs. None of the
functionality is lost, but the
graphical displays are!
(When *EXECed into another program
the wave change system
needs nearly 2500 bytes, 1800+
for words and the rest for
its run time arrays).
6) To get started...
First of all, RUN the program and check that the Pulse
waveform has been selected. (Type in a few note letters, or use a Music 4000
keyboard if you have one).
The screen should show the Pulse waveform plotted in the top
left of the screen, and indicate that the current waveform is a Geometric one
in the Harmonics window. (This just means that the current wave hasn't been defined
using harmonics).
Now enter 'Saw' at the % prompt.
The waveform should be redrawn, and playing a few notes
should confirm that a change has been made in the synthesiser waveform (the
tone will have changed markedly, into one that is much richer in high
frequencies).
Try the other two waveforms too. If you type 'help' at the %
prompt a list of the supplied waveforms is displayed. When you try Hwave you
will notice that a message is given as the three harmonics are processed.
To illustrate the use of harmonics use WZERO to initialise
the current waveform and then enter
127 1 WH!
80 2 WH!
40 4 WH!
20 6 WH!
WHG
WGC
wdraw
As each harmonic is processed a message is given. (This just
proves that the machine is working, as it does take a little time to do the processing!)
The new waveform will they be shown and can be played.
You can use 'edit' to get to Notepad and alter any of the
defined waveform words. (See notes below before starting!)
You will see that Square and Pulse use similar techniques,
while Saw has a little more maths to it. Hwave uses harmonic waveform creation.
Apart from the obvious range of facilities for experimenting
with waveforms that is provided, you can also create harmonic waveforms then, following
a WHG command, each value can be extracted using WG? for further changes.
To produce a range of more complex waveforms you may need to
'dump' the wave change words into your own program, to give extra working
space.
Notes
As the program stands, it uses quite a lot of the available
memory at run-time.
If you wish to create any new words, you must first create
some space by deleting existing ones. (The prime candidates must be the 'dump
facility' words 'dump', 'dump2' and 'dump3').
Note that, because of the way AMPLE works, you can create
new words when using Notepad, or even at the mode 4 prompt under some
circumstances, but get a '!No room' error when the program is RUN. You have
been warned!
I should like to acknowledge the contribution of Mike
Mellors, who both tested my program for the problem found in the
Soundsculptures software (see AMPLINEX 012), and provided the solution in the
form of the 'trans' word.
Related files on this disc:
U.Wave - Richard Bettis' waveform design and editing program
U.Preset1 - EXEC file of Music 500 waveform definitions courtesy
of Hybrid Technology
