The phase reversal and Amplitude Modulation that occurs around the 50% range of the SHAPE parameter
value is useful on it’s own (before FOLDing occurs) for subtle and pleasing modulations via LFO. The
SHAPE circuit is slow and smooth with a unique response quite unlike the typical balanced modulator or
VCA. When this element of the SHAPE circuit is utilized with FOLDing, the AM and Phase Reversal will act
to drop and/ or reverse folds resulting in deeper animation of the Timbre. When combined with slow modula-
tion of the FOLD and ANGLE parameters, it is possible to achieve extremely animated sounds with just a
single modulation source.
The ANGLE parameter injects a signal into the FOLD circuit at a node that results in pushing or tilting the
circuit to one side or another. The net result is quite dependent upon the SHAPE and FOLD parameters.
SINE shape results in Asymmetrical folding and additionally, thresholds of the FOLD circuit may be pre-ma-
turely exceeded resulting in linear amplitude loss in some FOLDs. It is almost subtractive in nature.
Where the ANGLE parameter really shines, is in the animation of the higher order harmonics added to the
signal by the SHAPE control. Slow modulation of the ANGLE parameter will push the SPIKE shape through-
out the entire wave cycle continuously, and the result sounds like a combination of Phase Shifting and deep
Pulse Width Modulation. The Glitched Triangle is a combination of the Asymmetrical folding and this Phase
Shift/ PWM effect. Again, slow modulation is the key here, giving the ear a strong and entertaining harmonic
to follow as it dances atop the long wave-cycles of the lower octaves. Perfect for animating bass lines. It
also adds shimmer to the upper octaves, especially when the rate of modulation is increased to the lower
audio registers.
The FOLD parameter is the final stage of the Timbre section and its behavior is greatly determined by the
SHAPE and ANGLE parameters. The first 30% or the parameter value will act as a VCA, and is useful for
creating percussive sounds. The after about 30% the FOLD circuit will reach its first threshold and from this
point on is nothing like a VCA.
When SHAPE is set to 0% and ANGLE is set to around 50%, the FOLD circuit is fed a symmetrical SINE
wave and increasing the FOLD parameter beyond 30% will result in the continuous introduction of lower-or-
der harmonics. This Additive process was unique to the Buchla instruments developed in the early days of
synthesis (Music Easel and 259 module) and is opposite to the process of filtering utilized for Subtractive
synthesis popularized by the Moog synthesizers (Minimoog). The sound is large and quite aggressive. While
it is the opposite of the filtering process it responds to modulations is a very similar way, with sweeping
envelopes, SINE or Triangle LFOs and Audio Rate modulations being quite effective.
When Shape is set to SPIKE or Glitched Triangle, there will be fewer of the lower order harmonics audible
and the higher order harmonics present in the SPIKE and Glitched Triangle signals will smear the sound
with soft noise. The FOLD circuit is not able to work perfectly with these signals, and the results are very
interesting.
On the reception of a Gate or Clock Pulse, STRIKE will very briefly open the FOLD circuit to 100%. STRIKE
is useful for creating percussive sounds, accents and audio rate modulation of the FOLD circuit.
Summary of Contents for DPO
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