25
The Oscillator Section
16 19 2317 18 20 21 22
The Oscillator section for each of Summit’s two synths consists of three identical
oscillators, each with its own set of controls. Therefore, the following descriptions apply
equally to any of the oscillators.
Oscillator Waveform
The Wave button
19
selects one of five wave shape options: four are the common
fundamental waves, Sine, Triangle, (rising) Sawtooth and Square/Pulse.
The fifth option, more, allows selection from a range of 60 further wavetables, accessed
by the WaveMore parameter in the Osc menu. The LEDs confirm the waveform option
currently selected. Note that the display immediately changes to the Osc menu, showing
the WaveMore parameter for the oscillator being adjusted, as soon as more is selected.
(see xxx).
Oscillator Pitch
The three controls Range
16
, Coarse
17
and Fine
18
sset the Oscillator’s fundamental
frequency (or Pitch). The Range button selects using traditional “organ-stop” units, where
16’ gives the lowest frequency and 2’ the highest. Each doubling of stop length halves
the frequency and thus transposes the pitch of a note played at the same position on a
keyboard down one octave. When Range is set to 8’, the keyboard will be at concert pitch
with Middle C in the centre. The LEDs confirm the stop length currently selected.
The Coarse and Fine rotary controls adjust the pitch over a range of 1 octave and
1 semitone respectively. The OLED display shows the parameter value for Coarse in
semitones (12 semitones = 1 octave) and Fine in cents (100 cents = 1 semitone).
Summit is not limited to traditional “Western” note intervals, nor to the standard equal-
tempered scale. You can reprogram the keyboard in almost any way by using Tuning
Tables; these are described in detail at page 26.
Pitch Modulation
The frequency of each Oscillator may be varied by modulating it with either (or both) LFO
2 or the Mod Env 2 envelope. The two Pitch controls, Mod Env 2 Depth
20
and LFO 2
Depth
21
control the depth – or intensity – of the respective modulation sources. (Many
other pitch modulation possibilities are available by using the Modulation Matrix – see page
38.)
Each Oscillator has a Depth control for modulation by Modulation Envelope 2. Adding
envelope modulation can give some interesting effects, with the oscillator pitch altering
over the duration of the note as it is played. A Mod Env 2 parameter value of 30 shifts the
pitch of one octave for the maximum level of the modulation envelope (e.g., if sustain is
at maximum). Negative values invert the sense of the pitch variation; i.e., the pitch will fall
during the attack phase of the envelope if Mod Env 2 has a negative value.
Each Oscillator also has a Depth control for modulation by LFO 2. Adding LFO Modulation
can add a pleasing vibrato when a triangle LFO waveform is used, and the LFO speed is
set neither too high nor too low. A sawtooth or square LFO waveform will produce rather
more dramatic and unusual effects. Oscillator pitch can be varied by up to five octaves,
but the LFO 2 depth control is calibrated to give finer resolution at lower parameter values
(less than ±12), as these are generally more useful for musical purposes.
Negative values of LFO 2 Depth “invert” the modulating LFO waveform; the effect of this
will be more obvious with non-sinusoidal LFO waveforms, e.g., with positive Depth values a
falling sawtooth LFO waveform will cause the oscillator pitch to lower and then rise sharply
before lowering again, but if Depth has a negative value, the pitch variation will be the
opposite.
Waveform Shape
Summit lets you modify the shape of the selected waveform; this will alter the harmonic
content and thus the timbre of generated sound. The degree of modification – or deviation
from the original waveform shape – can be varied both manually and as a modulation. The
modulation sources available using the panel controls are Mod Env 1 and LFO 1; any other
mod source may be selected using the Modulation Matrix – see page 38
The Source button
23
assigns the Shape Amount control
22
to adjust the amount of
waveform alteration by one of the three sources. Note that all three possible sources –
Manual, Mod Env 1 and LFO 1 may be used in any combination, each with a different
value of Shape: their effect is additive.
When set to Manual, Shape lets you alter the waveform shape directly; the parameter
range is -63 to +63, where 0 results in an unmodified waveform. The sonic effect of Shape
will depend on the waveform in use.
When Sine is selected as the waveform, a non-zero Shape parameter causes the sine
wave to become asymmetric, resulting in the addition of upper harmonics. Varying Shape
with Triangle or Sawtooth waveforms also modifies the wave shape and thus the harmonic
content.
When Square/Pulse is selected as the waveform, Shape will vary the pulse width: a value
of 0 produces a 1:1 square wave. The timbre of the “edgy” square wave sound can be
modified by varying the pulse width, or duty cycle, of the waveform. Extreme clockwise
and anticlockwise settings of Shape produce very narrow positive or negative pulses,
with the sound becoming thinner and more “reedy” as the control is advanced. When
fully anticlockwise (parameter value -64), the square wave assumes a duty cycle of 0%
and is thus “off”. When varied to this degree by, e.g., adding LFO modulation, a rhythmic
character can be added to the oscillator waveform.
When Wave
19
is set to more, Shape sweeps through the wavetable’s waveform
(selected by the WaveMore parameter in the Osc Menu) by interpolating across the five
indexes of the selected wavetable to produce a “morphing” of two adjacent indexes: the
sonic effect of this will vary greatly depending on the active patch and the wavetable in
use. Each wavetable is actually a bank of five waveforms, between which the user can
interpolate with the Shape control. We recommend you experiment altering Shape with
different waveforms to hear the effect. See also the WaveMore menu option described
below.
Waveform shape may be modulated further by either (or both) Mod Env 1 or LFO 1, with
the amount of waveform modification due to each individually adjustable by Shape,
according to the setting of Source. With pulse waveforms, the sonic effect of LFO
modulation is very dependent on the LFO waveform and speed used, while using envelope
modulation can produce some good tonal effects, with the harmonic content of the note
changing over its duration.
The Oscillator Menu
The following additional Oscillator parameters are available in the Osc menu. Each of
the three oscillators has two menu pages; the parameters available for each oscillator
are identical. There are also two further pages (OSC COMN pages, 1/8 and 2/8), with
parameter controls common to all three oscillators.
Common Oscillator pages:
The parameters available on the Common menu pages affect all three oscillators.
The default menu display is shown below:
OSC COMN 1 1/8
Diverge 0 H
Drift 0
TuningTable 0
OSC COMN 2 2/8
KeySync Off H
Noise LPF 127
Noise LPF 0
Diverge
Displayed as: Diverge
Initial value: 0
Range of adjustment: 0 to 127
Each Voice is generated by three oscillators within the FPGA, giving a Summit a total
of 24 oscillators. Diverge applies very small pitch variations independently to each of
these 24 oscillators. The effect of applying this is that each voice will have its own tuning
characteristic. This adds a further interesting colouration to the sound quality and can be
used to bring the synth alive. The parameter sets the degree of variation.
Try setting BendRange to different values for each of the three oscillators.
This can produce some interesting triad chords when the pitch wheel is
moved.
To Next Page
Loading...
