Filter slots
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” parameter 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 parameters, will be kept even if you change the filter type.
Ladder LP Filter
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 another to Filter 2). The pre-defined routings of the three oscillators into the Filter 1-2 sections is described in the “Basic connections - a tutorial” passage.
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 reproduced 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 output but before the feedback loop. • Type II - The shaper (controlled with the Drive parameter) is placed at the filter input 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 clockwise will produce 12 semitones/octave tracking.
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) parameter 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.
THOR POLYSONIC SYNTHESIZER
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