tone color refers mainly to the harmonic over tone structure of
each musical note. Tone color or timbre is a complex acoustical
phenomenon, and we are limited by present day technology in our
ability to sense it or represent it as a control voltage. The closest
thing to a "timbre" extractor that we have in present
day musical products is a vocoder, which samples the signal's overtone
structure in a number of different frequency bands, and converts
the output of each frequency band into a control voltage. This would
present an information overload in present instrument-controlled
synthesizer architectures. A simpler method of approximating a "tone
color" parameter makes use of the fact that, in most musical
instruments, the overtone structure is "brighter" (contains
more harmonics) as the instrument 's loudness increases. The relationship
between brightness and loudness is not simple, but we can link loudness
and timbre together and obtain pleasing results. So the bright-
ness parameter is a control voltage derived from the loudness parameters.
In figure 1,
the system components for parameter extraction in an instrument-controlled
synthesizer are shown. In Figure 2, a musical sequence and its associated
control parameters are displayed. By studying these diagrams, you
will have a good idea of the process of parameter extraction.
ARCHITECTURE OF AN INSTRUMENT-CONTROLLED SYNTHESIZER
In the last
section and in Figure 1, we constructed a system to derive control
parameters from a musical signal input. This system is essentially
the front end of an instrument-controlled synthesizer. It functions
as the interface between the input signal and the synthesizer guts
the same way as the mouthpiece and buttons on a saxophone function
as the performer interface. You play the saxophone with your lungs,
embouchure and fingers through the mouthpiece and buttons; and in
the same way you play the instrument-controlled synthesizer with
the output of your saxophone through the instrument-interface system.
The rest of
the instrument-controlled synthesizer is essentially a voltage-controlled
synthesizer, similar in many ways to all the synthesizers produced
since Moog put out his first one in the 1960's. The available products
differ markedly in their approach to synthesis systems, but they
all employ adaptations of basic synthesizer elements. (In Part 2
of this article, we will go into specifics.)
synthesis section connects to the instrument-control interface by
means of the control parameters derived from the musical instrument
input. Figure 3 shows this basic system, while figure 4 provides
a detailed representation of the subsystem components.
section consists of one or more voltage controlled oscillators,
a voltage-controlled filter, voltage-controlled amplifier, and one
or two envelope generators. The interconnection between the synthesis
components and the control interface components is dependent on
the complexity of the synthesizer. The system of figure 4 represents
a complex system which makes full use of all the information we
have gathered about the musical sound, as described earlier.
oscillators, which form the basic tone-generation system for the
synthesizer, are controlled by the output of the pitch follower.
Thus, the synthesizer will provide tones which track the pitch of
the input signal, either in unison or at some musical interval selected
by the user.
VCO outputs are filtered by the voltage-controlled filter to provide
the desired tone color. In a standard synthesizer, the voltage-controlled
filter is swept by an envelope generator to create a spectral envelope.
In the instrument-controlled synthesizer depicted here, we have
the option to make the filter much more responsive to the musical
information we derived from the input signal. By controlling the
amplitude of the filter envelope with the brightness control voltage,
we can make the synthesizer's tone color more life-like, responsive
to the musical expression contained in the brightness of the original
signal. Alternatively, we can control the voltage-controlled filter
by the output the envelope follower, so that the filter's "contour"
exactly duplicates the instrument's loudness envelope. This would
simulate the familiar "envelope-controlled filter" musical
effect, except that in this case a synthesized signal is filtered
instead of the controlling instrument's own signal. Both methods
of dynamic filtering are found on currently available instrument-controlled
amplifier, which provides the amplitude contour of the filtered
signal, is driven by a control voltage from the VCA envelope generator.
Once again, the envelope generator can be controlled by the loudness
parameters detected by the instrument parameter extraction system.
This kind of control will give the instrument-controlled synthesizer
a realistic set of loudness dynamics responsive to the input signal.
Not all instrument-controlled
synthesizers have this degree of sophistication and dynamic interaction
with the controlling musical instrument. The essential elements
of instrument-controlled synthesis systems, as described, are the
basis for all product designs that have appeared.
USING AN INSTRUMENT-
At a recent
NAMM convention, Don Tavel of Musico (makers of the Resynator Instrument
Controlled Synthesizer) made a comment which sums up the essence
of the proper use of instrument-controlled synthesizers. "A
guy comes up to play the Resynator, which is set up to sound like
a trumpet. He is playing it with the guitar, but instead of playing
with trumpet dynamics and trumpet phrasing, he is using guitar dynamics
and guitar phrasing. How does he expect it to sound like a trumpet
unless he plays it like a trumpet? "That is a very subtle statement,
actually. It means that you want to play "through" the
whole system with the end product in mind. It implies a knowledge
and "pre-visualization" of the final sound and articulation
you want to convey. Most important, it calls for a musical technique
which en- compasses the characteristics and limitations of both
your native instrument and your instrument-controlled synthesizer.
Guidelines for playing instrument-controlled synthesizers are very
similar to guidelines for playing any musical instrument, once you
understand that your musical instrument's output (rather than your
fingers) is playing the synthesizer. Playing "clean" and
"distinctly" will yield the best results. You really,
at first, have to "tell" the instrument exactly what you
want. If you are a wind player, remember that breath noise and indistinct
note transitions will provide misleading information to the pitch
and envelope-follower circuits. If you are a guitar or keyboard
player, remember that you need to play one note at a time. This
may seem easy; but you should realize that strings can vibrate from
harmonic excitation, or shocks to the musical instrument, or imprecise
playing. Any of these additional "noises" will throw off
even the best pitch-to-voltage converter. On the guitar, you can
learn to "damp" strings with the fleshy parts of either
hand, allowing only the melody string to vibrate. Pickups and tone
controls on the instrument should be adjusted to provide maximum
volume and a strong fundamental. On a guitar, the center pickup
is usually best. Sometimes, on an instrument with a low output level,
preamplification can help. Each available instrument-controlled
synthesizer has one or more "sensitivity" or input controls.
Finding the optimum settings of your instrument's controls and the
synthesizer controls will pay for the time spent. Once you master
the techniques to make the synthesizer track your instrument optimally,
you will be ready to explore the subtleties of the synthesizer.
Many differences exist in the form and layout of the "synthesizer"
controls on different instrument-controlled synthesizers. In fact,
some notable advancements in synthesis technology have appeared
in these products. In the next article, I will discuss some of the
commercially available products with the objective of exploring
their different approaches to synthesis techniques. I hope your
interest in these new products has been stimulated, and that you
will help bring them into the musician's repertoire of performing
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