The next set of components I would like to talk about are Thor’s
filters. Each filter has a unique
function that can be used to cut harmonic content and shape a sound (called
subtractive synthesis).
So lets take a look at the filters:
Low Pass Ladder Filter
This filter is just a “simple” low pass filter. I say “simple” because it only has a single
function: filtering out high-frequency content.
On the filter you have the capability to set the filter frequency and
resonance level. There are also controls
that alter how the filter is effected by the filter envelope, velocity, and
keyboard position. You can also invert
these functions as well as increase the amplitude with a linear slider labeled
“drive”. In addition, there is a
selector switch that alters the slope (2x 24dB/18dB/12dB/6dB per octave).
The final selection switch turns on the ability for this
filter to self-oscillate. A
self-oscillating filter can create a sine wave when the resonant frequency is
high enough to oscillate itself.
State Variable Filter
The state variable filter is more of jack-of-all-trades
filter. In addition to the common
modulator functions, frequency/resonance selectors and “drive”, the State
Variable filter allows you to change its function between Low Pass filter, High
Pass filter, Band Pass filter, Notch filter or Peak filter. You can also alter how close to
high-pass/low-pass the peak and notch filters act.
Comb Filter
The comb filter is an interesting component that is normally
used to add a chorus/flange-like effect to a sound. This effect is achieved by taking a clone of
the incoming signal, and delaying it slightly before summing the two signals
back together. This causes phase
summation and cancellation at different intervals (when used with a pure sine
wave). When using more complex wave
forms, more interesting “resonant regeneration” occurs. There is a +/- selector that allows you to
invert the resonant peaks caused by the phase modulation creating a slightly
different sound.
Formant Filter
The formant filter is similar to the “wha” guitar effect
pedal in that it can emulate the consonant “w” along with different vowel
sounds (based on the spectral content of
the input signal). The formant
filter in thor allows you to replicate different consonants and vowel sound (albeit
on a limited scale – nowhere near the ca[abilities of the human voice) in
addition to changing the “gender” of the signal (most likely by altering the amplitudes
of the lower frequencies). The filter
itself is controlled by a virtual X/Y pad, which can be manipulated (and even
modulated via Thor or automation) to sweep through multiple consonants and
vowels. So how is this achieved? Formant filters act like multiple band-pass
filters acting on the same signal at the same time.
This is just a brief look at Thor’s filters. For more in-depth information, visit
Propelloheads’ series called Thor Demystified,
or this article from Reason Experts.
Next week I will take a closer look at modulation sources
and the modulation bus matrix. Thanks
for reading and I hope you get a chance to play around with Thor!
