Operation Manual

THOR POLYSONIC SYNTHESIZER
211
Filter slots
Thor has three open Filter slots, two in the Voice section (which act per-voice) and
one in the Global section which is global for all voices (see “Global Filter slot”).
D You select (or change) filter type for a slot by clicking the arrow button in
the top left corner of a slot.
On the pop-up you can select between 4 filter types and bypass mode. Available
filter types are Ladder LP, State Variable, Comb and Formant, each described
separately below.
The following general rules apply:
D Filters are pre-wired to the Filter Envelope (see “Filter Envelope”).
• Filters 1 & 2 can be used serially (i.e. the output of Filter 1 goes (via the Shaper) to
the input of Filter 2, or in parallel (meaning that one signal goes to Filter 1 and an-
other to Filter 2).
The pre-defined routings of the three oscillators into the Filter 1-2 sections is de-
scribed in the “Basic connections - a tutorial” passage.
Common parameters
As with the open oscillator slots, there are certain parameters which are common for
all filter types.
These are as follows:
D All the filter types have large knobs for the filter frequency (FREQ) pa-
rameter and the filter resonance (RES) parameter.
This works slightly differently for the Formant filter - see “Formant filter”.
D The “KBD” parameter sets how the filter frequency tracks incoming note
pitch data.
Some filter types (Ladder/State Variable/Comb) can “self oscillate” and be used
as extra oscillator sources.
D The “ENV” parameter sets how much the filter frequency responds to the
Filter Envelope.
D The “VEL” parameter sets how much incoming note velocity affects the
Filter Envelope Amount.
In other words, for this parameter to have any effect it requires that the “ENV” pa-
rameter is set to a value other than zero.
D The “INV” button inverts how the filter frequency responds to Envelope
settings.
D The “Drive” parameter allows you to adjust the input gain to the filter.
By driving the filter harder you can add further character to the sound.
D Any parameter settings, as well as any modulation assigned to parame-
ters, will be kept even if you change the filter type.
Ladder LP Filter
The Ladder LP filter is a low-pass filter inspired by the famous voltage controlled filter
patented by Dr. Robert Moog in 1965. The name originates from the ladder-like shape
of the original transistor/capacitor circuit diagram.
The original filter also had certain non-linear characteristics which contributed to the
warm, musical sound it is renowned for. These characteristics are faithfully repro-
duced in the Ladder LP filter.
There is also a built-in shaper in the feedback (self-oscillation) loop. If self-oscillation is
activated (see below), the shaper will distort the sound to produce these non-linear
characteristics. To adjust the intensity of this distortion you use the Drive parameter.
D There are 4 different Filter slopes available; 24, 18, 12 and 6 dB/oct.
24dB slope comes in two different types:
• Type I - The shaper (controlled with the Drive parameter) is placed at the filter out-
put but before the feedback loop.
• Type II - The shaper (controlled with the Drive parameter) is placed at the filter in-
put after the feedback loop.
Note that “Self Osc” (see below) must be activated for the shaper to operate.
D This filter can self-oscillate and will produce a playable note pitch with
high Resonance settings if this is activated.
Self-oscillation can be switched on or off by using the “SELF OSC” button. The
“KBD” knob governs how the frequency tracks the keyboard, turned fully clock-
wise will produce 12 semitones/octave tracking.