EWMOD - An Envelope and Waveform Modification Module for the Music
This document describes a software module which enables modification of
envelopes and waveforms for the Music 5000 synthesiser.
This document and the program described in it are copyright (C) 1989-1995,
Angus J. C. Duggan.
A tar archive containing a PostScript version of this document and
the program itself is available from
This document describes a software module which enables modification of
envelopes and waveforms for the Music 5000 synthesiser. The module requires
the M5 module from the Music 5000 Release 2 software to be available.
The EWMOD module is designed as a core module for use by envelope and
waveform editors, presenting a minimal set of words for use. Conversion of
parameters from easily understandable forms are described in the cases where
data is required in awkward forms.
Envelopes are used to modify the amplitude or pitch of notes as they play.
Envelopes in the Music 5000 system consist of three sections, each of which
may be as simple or complex as required. The pitch or amplitude of an envelope
at any point is referred to as the level of the envelope.
The on section defines what happens to the level of the envelope when
a note is started. When the on section has finished, the note enters
the repeat section, which is continually repeated until the note
is turned off or on again.
When the note is signalled to turn off, the envelope enters the off
section, and when the off section has finished the envelope level
returns to zero until the note is turned on again.
Each section of an envelope is made up of zero or more segments. Each
segment has a gradient and a target level. The gradient
defines how quickly the envelope level changes to the target level from its
current level. An envelope will never overshoot the target level, and the
envelope will always wait until the target level is reached before moving on
to the next segment.
The M5 module provides 110 segments to be shared between 34 envelopes.
There are no restrictions on the number of segments allowed in any individual
envelope or section except the overall total. The envelopes are numbered from
0 to 33, and the M5 module assumes a convention by which envelopes 0-15
are pitch envelopes, envelopes 16-31 are amplitude envelopes, and envelopes
32 and 33 are default envelopes which should not be modified. It is suggested
that this convention is followed, to prevent confusion between pitch and
The words in the EWMOD module which operate on envelopes are -
Waveforms define the pressure fluctuations which characterise a sound. The
Music 5000 synthesiser is capable of storing 14 waveforms of 128 points each,
and modulating these waveforms using a variety of special effects. The
waveform defining system provided by EWMOD allows more waveforms to be
prepared and loaded into the Music 5000 as desired. The waveforms are numbered
from 0 to 13.
- first last Eclr
- This word clears the envelopes from first to last,
freeing the segments used by them for use. Envelopes can be redefined
without clearing them first, but if a large number of segments are
required extra envelopes may have to be cleared to make space.
- on repeat off scale envnum Emake
- This word redefines the envelope specified by envnum. Any
segments used by envelope envnum are freed for use, and then
the number of segments specified by on, repeat, and
off parameters are allocated to the envelope. The number of
segments allocated to any section can be zero, in which case the section
is ignored. If zero repeat segments are specified, the level of the
envelope will remain constant at the final level of the on section until
the note is turned off.
The scale parameter indicates whether the levels should be
magnified. A negative scale indicates that no magnification should be
performed, zero indicates that levels should be multiplied by 4, and a
positive scale indicates that levels should be multiplied by 16. Scaling
is especially useful for pitch envelopes which are required to sweep a
large pitch range.
No initialisation of the segments allocated is performed, so all segments
must be redefined for the envelope.
Note that most envelopes will have a segment at the start of the on
section which resets the level to zero immediately, so that all
subsequent changes can take place on a know timescale.
- gradient level segnum Eseg
- This word redefines the segment number segnum, in the envelope
last initialised by Emake. Segments are
numbered from 0 up to
one less than the total number of segments in the on, repeat, and off
sections. The level parameter specifies the target level at
the end of the segment, and the gradient parameter specifies
the rate at which to alter the level.
The level parameter is the target volume or pitch change plus 127. For
amplitude envelopes, only values in the range 127-255 are meaningful,
corresponding to amplitudes of 0-128. For pitch envelopes, the full range
of 0-255 can be used, corresponding to -127 to +128 pitch units. The size
of the pitch units depends upon the scale set by Emake - it will be 1/16 semitones for a negative
scale, 1/4 semitones for a zero
scale, or 1 semitone for a positive scale.
The gradient can be calculated by multiplying the magnitude of
the level change desired by 256, and dividing the result by the number of
time units over which the change is to take place. Each time unit is
approximately 10 milliseconds. Note that the gradient is not signed; the
direction in which the level will change is defined by the difference
between the current level and the target level.
A gradient of zero should not be specified; if a long period with no
change is desired, a level difference of 1 should be specified, with a
gradient sufficiently shallow to take up the time required.
- envnum Eset
- This word sets the envelope indicated by envnum to be the
pitch or amplitude envelope for the current channel selection. The M5
words AEN and PEN should be used to distinguish
whether the envelope is to be set as the amplitude or pitch envelope.
The system used in EWMOD revolves around waveform buffers. These
are 128 word arrays which are provided by the programmer (possibly by writing
128 DIM ARRAY). If waveforms are set at the start of a program and
never altered afterwards, one buffer can be used to build all of the waveforms
in turn. If waveforms are to be altered during execution of a program it is
better to build all of the waveforms required in different buffers, and then
load them from the buffers when required. Another advantage of using buffers
is that words can be written using the normal load and store operators to
perform filtering or other operations on
partially generated waveforms. Note: the size of the buffer provided is not
checked by any of these words, and so use with a wrongly sized or addressed
buffer will probably corrupt the program. It is recommended that programs
modifying waveforms are saved before running.
- buffer Wclr
- This word resets the waveform in buffer to be zero at all
points. This is usually necessary before using Wharm.
- size harmonic buffer Wharm
- This word adds a harmonic component to the waveform in buffer.
The harmonic specified by harmonic should be in the range
1-16. The size of the smallest component specified by size
should be 256, where possible. Wmax can be
used to rescale to waveform.
- height1 height2 length from Wline
- This word creates a straight line segment in a waveform. The start
address of the segment is passed in the parameter from, and
the length of the segment is specified by length. The
parameters height1 and height2 specify the levels
at the start and end of the line segment respectively. Wline
allows waveforms which could not be created by Wharm to be created easily. Note: from
is the segment start address, not the buffer start address.
- buffer wavenum Wmake
- This word loads the waveform specified by buffer into the
Music 5000 as waveform number wavenum. It also performs a
Wset to set the waveform on the current
- buffer Wmax
- This word rescales the waveform stored in buffer, so that the
largest amplitude of any point on the waveform is &7F00. This gives
the largest sensitivity to amplitude changes that the waveform can have.
Wmax is not needed in cases where the
maximum amplitude is known to be &7F00 already.
- wavenum Wset
- This word sets the waveform indicated by wavenum to be the
waveform used by the current channel selection.
Here are some examples of words which use EWMOD - the first two words
define a pitch envelope for an increasing vibrato and a soft-edged amplitude
- Invalid envelope
- This error occurs when an envelope number outside the range 0-33 is used
with Eclr, Emake or Eset.
- Invalid harmonic
- This error occurs when a harmonic number outside the range 1-16 is used
- Invalid length
- This error occurs when the length parameter to
Wline is outside the range 1-128.
- Invalid segment
- This error occurs when a segment number is used which is outside the
range 0 to x-1, where x is the total number of on,
repeat and off segments in the current envelope. The current envelope is
the envelope specified by the last Emake.
- Invalid waveform
- This error occurs when a waveform number outside the range 0-13 is used
in Wset or Wmake.
- Too many segments
- This error indicates that all of the free envelope segments have been
used up. Segments can be freed by clearing unwanted envelopes with
Eclr. If there are still not enough
segments, one or more
envelope definitions may have to be simplified. If envelopes are not used
simultaneously they can share the same envelope number, but care must be
taken to ensure that notes using the previous envelope have finished
playing before re-using the envelope number.
"incvib" [ % increasing vibrato
6 2 0 ON 0 Emake % no off section, normal scale
&7F00 127 0 Eseg % pitch 0 immediately
&0010 126 1 Eseg % pitch -1 in 16 steps
&0030 129 2 Eseg % pitch +2 in 16 steps
&0060 123 3 Eseg % pitch -4 in 16 steps
&00A0 133 4 Eseg % pitch +6 in 16 steps
&00E0 119 5 Eseg % pitch -8 in 16 steps
&0200 135 6 Eseg % pitch +8 in 16 steps
&0200 119 7 Eseg % pitch -8 in 16 steps
0 PEN Eset % make current pitch envelope
"soft" [ % soft attack
3 0 2 ON 16 Emake % no repeat section, normal scale
&7F00 127 0 Eseg % start at 0 amplitude
&3800 239 1 Eseg % amplitude 112 in 2 steps
&0200 255 2 Eseg % amplitude 128 in 8 steps
&2000 158 3 Eseg % amplitude 31 in 3 steps
&0100 127 4 Eseg % amplitude 0 in 31 steps
16 AEN Eset % make current amplitude envelope
The next words define a triangular wave and a ``reedy'' wave (waveforms with
odd harmonics tend to produce sounds similar to reed instruments). Both of the
words use the same waveform buffer, but separate buffers could be used if
"buffer" [ % waveform buffer
128 DIM ARRAY
"triangle" [ % triangular wave
0 100 32 1 buffer Wline % rise until 1/4 wave
100 -100 64 32 buffer Wline % fall until 3/4 wave
-100 0 32 96 buffer Wline % rise until end of wave
1 buffer Wmax % scale wave
"reedy" [ % reed like sound
1 buffer Wclr % clear buffer
100 1 1 buffer Wharm % strong first harmonic
80 3 1 buffer Wharm % strongish third harmonic
60 5 1 buffer Wharm % medium fifth harmonic
40 7 1 buffer Wharm % weakish seventh harmonic
1 buffer Wmax % scale wave
"select" [ % select buffer as wave 1
1 buffer 1 Wmake % set waveform and select
Last modified on 12th February 2004 by email@example.com