Pixie Attaché
– an EDP WASP clone
ELBY Designs
– Laurie Biddulph
Kariong, NSW 2250, Australia
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SECTION II - The Oscillators
An oscillator can be considered to be any medium that is vibrating. A ruler
that is twanged over the edge of a desk, or a string on a guitar when plucked,
are both examples of oscillators. In the case of the Pixie Attaché the medium
involved is electricity. The oscillator is the basic building block of all
synthesisers.
In the Pixie Attaché there are two separate oscillators. The pitch of the
Oscillator (its rate of vibration) is determined by several factors:
(1) The keyboard, which controls the oscillator over a three-octave
range (C to C).
(2) The transpose control (4), which steps the oscillator over five
octaves. To see it's effect, hold down middle C and turn the
[TRANSPOSE] control (4) down to '-2', up to '+2' and then back to
'0'.
(3) The [MASTER TUNE] control (1); see Section V.
All these parameters affect the pitch of Oscillator DCO 1. In addition to having
variable pitch, the actual way in which the oscillator vibrates, known as the
wave shape or waveform, can be modified.
The five-position [WAVEFORM] selector (6) is used to switch the oscillator to
give square, sawtooth, triangular or sine wave shapes. These wave shapes
are shown in Figure 2
.
Figure 2 Oscillator Wave Shapes
A fifth waveform provides a fixed pulse-width modulated square wave.
ACTION:
Set the controls as per Figure 1. Only DCO 1 should be heard when playing a note.
ACTION:
Switch between the different wave shapes (6) and listen to the difference in tonal quality
between the waveforms. The sawtooth wave, for example, has a reedy sound while the
rectangular wave has a hollow quality to it. In addition, the rectangular wave can be modified
using the WIDTH control (5).
ACTION:
Select the square wave (6) and then turn up the [PULSE WIDTH] control (5). This has the
effect of increasing the positive period of the vibration cycle whilst increasing the period of the
negative part (see Figure 3).
As you turn up the [PULSE WIDTH] control (5) the tone of DCO 1 will become thinner with
more complex harmonics.
