ï~~GRAPHICS INTERFACES FOR MIDI-EQUIPPED SYNTHESIZERS
Przemyslaw Prusinkiewicz
Department of Computer Science
University of Regina
Regina, Saskatchewan, Canada
ABSTRACT
This paper explores methods of controlling synthesizer
parameters based on manipulating graphics objects on a
bit-mapped screen. A variety of computer generated
graphical controls is proposed. Programs implementing
graphical controls on a Macintosh microcomputer interfaced with a DX7 synthesizer are outlined.
1. INTRODUCTION
"Mathematics and electronics afford us increasingly powerful
means of dealing with data. But at the same time they multiply the number of arbitrary choices without changing our
natural means of perception the slightest. It thus comes down
to utilizing these natural means the best way."
Jacques Bertin (1983)
"The most important factors in the computer's seduction have
to do with the specificity of the computer as a medium to
support the desire, the needs and in extreme cases the obsession for 'perfect mastery'."
Sherry Turkle (1984)
Creating new voices (patches, instruments) using many
contemporary synthesizers is difficult. There are several
reasons for this. The number of controllable parameters
is large - often more than one hundred. This is
intended to maximize the flexibility of the instrument.
At the same time, the number of physically manipulable knobs (or slide potentiometers) is kept small in
order to minimize the instrument cost. Consequently,
one knob can be used to input values of many parameters. This creates two problems. First, a parameter cannot be immediately accessed - a knob must be assigned
to a parameter before its value can be changed. This
routing may involve changing the state of several
switches. Second, it is no longer possible to discern
current values of parameters just by looking at the control panel because the assignment of knobs to parameters is not fixed. At the same time the user needs a particularly clear, well-organized and comprehensive
access to data because of the large number of parameters involved. The need for a good user interface is
reinforced if some parameters have a nonintuitive character and their impact on the final sound is difficult to
conceptualize. If parameters cannot be made intuitively
obvious, they should at least be easily controllable in
order to facilitate experimentation.
In contemporary MIDI-equipped synthesizers, all or
most parameters can be remotely controlled by a computer. This opens a world of new interactive techniques
applicable to the design of interfaces between man and
synthesizer. The purpose of this paper is to present
some techniques based on manipulating graphical
objects on a bit-mapped screen.
The idea of of using a graphics interface to control
sound synthesis parameters is not new. Buxton et al.
(1982) described the application of "graphic potentiometers", bar graphs and function plots for this purpose. A
graphics interface was also included in the console for
the Lucasfilm audio signal processor (Snell 1982). However, the growing availability of workstations and
microcomputers with powerful interaction-handling
hardware and software encourages further research in
this area. Due to the decreasing cost of computer
hardware, graphics interfaces need no longer to be
confined to expensive computer music studios. They
may become the standard tool for controlling commercially available synthesizers.
This paper presents five approaches to the design of
graphical interfaces between man and synthesizer.
They were implemented on a 512K Macintosh (*) controlling a DX7 synthesizer. An Apple IIe (**) with a
Roland MPU-401 MIDI Processing Unit provided the
RS-232 - MIDI interface (Fig. 1). (For debugging purposes, the exchanged messages were also displayed on
the Apple He screen.) New controls were first drafted
using MacPaint (**) and after a satisfactory appearance
was achieved, they were implemented in software. All
programs were written in C (Manx 1983, 1984, 1985)
and rely heavily on the Macintosh firmware (Apple
1984, 1985).
(*) Macintosh is a trademark licenced to Apple Computer, Inc.
(**) Apple Hle and MacPaint are trademarks of Apple Computer, Inc.
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ICMC '85 Proceedings
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