|AudioMulch Help > Contraption Reference > Filters
SouthPole applies a resonant low-pass filter and gain control to an audio input. Gain, along with the filter's cutoff frequency and resonance can be controlled by a number of built in modulators. The modulators are:
- 3 ADSR envelope generators that can be triggered by clock-synchronized patterns, external audio input, or a combination of both.
- 2 LFOs (low frequency oscillators) that can be clock synchronized or free running.
- Envelope followers that follow the amplitude of an audio input.
This contraption synchronizes to the global clock. Remember to press play (applies to clock sync low frequency oscillators and pattern triggered ADSR envelope).
See the Adjusting Contraption Properties section for information about using sliders, knobs, presets etc.
Base Parameters and Modulation
The Cutoff, Resonance and Gain knobs, all in the Base column, control the base levels of these parameters.
Cutoff controls which frequencies will be audible from your input sound. As Cutoff controls a low-pass filter in SouthPole, frequencies above the set level are attenuated, thereby allowing the lower frequencies to pass. This affects the timbre of the sound, i.e. how bright or mellow it sounds.
Resonance controls how much the frequencies around the Cutoff frequency are increased in volume. This parameter also affects the timbre of the sound, and can be used to add a more nasal quality to the filtering.
Gain controls the overall volume of the sound before it leaves the contraption.
Each of these parameters can be modulated by a combination of modulation sources using the 24 knob modulation mixer at the bottom of SouthPole's Property Editor. Each source has a mixer knob on the same row as each of the Base parameters. The modulation sources are: Input Follower, Side Chain Follower, Envelopes 1-3, and Low Frequency Oscillators 1 and 2 (LFOs).
The modulation sources are summed with (added to or subtracted from) the base value of each parameter by an amount determined by the corresponding mixer knob.
Base parameter values are expressed in the natural units of the parameter (Hz for frequency, dB for gain), but modulation knobs specify a modulation amount ranging from -1.0 to +1.0, which represents a proportion of the full scale Base parameter range. When set to 0.0, the modulation knob has no effect on the parameter. Turning clockwise (+ values) adds the modulation source to the corresponding base parameter. Turning anti-clockwise (- values) subtracts the modulation source from the corresponding base parameter.
Envelopes (Env 1 – Env 3, Attack (A) Decay (D) Sustain (S) and Release (R) knobs, Gate Duration, Trigger Source)
There are three identical, pattern-sequenced ADSR envelopes in SouthPole (Envelope 1, 2 and 3). With the Attack (A), Decay (D), Sustain (S) and Release (R) knobs you can control the attack, decay, and release times, as well as the sustain level. You can also control the Gate Duration (the time from when the envelope is triggered until the start of the release segment.)
The envelope can be triggered by the Pattern Editor, or by an external input, or a combination of the two. See the following sections for a discussion of external input triggering and the Pattern Editor used for pattern sequencing.
Envelopes can be positive or negative, depending on the relative settings of the Base Cutoff and Env 1-3 Cutoff. Positive Envelope amounts cause the envelope to sweep upwards, and negative values cause it to sweep downwards.
Envelope Trigger Source
Trigger Source lets you trigger the envelope in a number of ways: Pattern (triggers the envelope with the pattern in the Pattern Editor); Input Trigger (derived from the main audio input signal and controlled by the Input Trigger section at the top of the editor); Side Chain Trigger (derived from the side-chain input and controlled by the Side Chain Trigger section at the top of the editor); or by combining the pattern with the external triggers (Input, Side Chain) so that the envelope only triggers when both a pattern trigger is present and an external trigger is also detected (Pattern * Input Trigger and Pattern * Side Chain Trigger).
External Audio Triggers (Input Trigger and Side Chain Trigger)
SouthPole's external audio triggers are simple mechanisms that can be used to trigger an envelope when the incoming audio signal exceeds a threshold. For example, the threshold can be set to detect the onset of percussive sounds such as a drum beat. The Input trigger responds to the audio signal which feeds SouthPole's filter. The Side Chain Trigger responds to SouthPole's second “Side Chain” input.
Both the Input Trigger and the Side Chain Trigger may be used to trigger any of the three envelopes by selecting them using the Trigger Source settings described above. The controls for the triggers are located at the top of the contraption editor. Each trigger has two parameters: Threshold and Delay. Threshold determines the lowest input level that causes a trigger to be generated. Delay determines the time that the trigger generator waits after generating a trigger before generating another trigger - this may be useful with some types of input to prevent multiple triggering.
The pattern editor displays a rhythmic matrix, which determines the rhythmic pattern used to trigger the envelope (if Trigger Source is set to Pattern – see above). The pattern consists of a matrix of equally spaced cells. You can vary the spacing of the cells, the pattern (loop) length and include one or more time signature changes. Bar and beat numbers are marked along the top of the matrix. By default, the cells are spaced a sixteenth note (semiquaver) apart within a two bar loop of 4/4 time.
The Triggers row indicates the on/off state of each note in the rhythmic pattern. The Ties row indicates whether a note is tied to the following note. Cells in each row can be toggled on and off by clicking on cells. Click on a cell and drag to "paint" (toggle) multiple cells without releasing the mouse.
To select a different rhythmic value (instead of semiquavers) for the cell spacing, click on the drop down list at the upper left of the pattern editor and select the desired value. You can also add customized rhythmic values by selecting Other... from the list and entering new values.
There are two identical LFOs (low frequency oscillators) in South Pole. As the name suggests, a low frequency oscillator oscillates slowly, typically slower than the speed we usually associate with audio frequencies, i.e. slower than 20 cycles per second, and often much slower. Thus, they're useful for creating rhythmical or slowly modulating changes to the filter settings.
Each LFO has a variety of waveforms that you can choose from the drop-down menu. Each LFO also has two basic modes: Clock Synchronous and Asynchronous.
The Clock Synchronous mode lets you create LFOs that stay in time with the beat (cycling every 8 bars for example). The Period parameter determines the duration of a single LFO cycle, expressed in rhythmic units. Select the unit you want from the drop-down menu. By default, the unit is 1/16, a sixteenth note (semiquaver).
Use the Phase setting to adjust the phase of the oscillator. When set to 0.0 (default), the waveform is aligned with clock time. The phase is expressed in the same unit as the period. Changing this setting offsets the waveform by this amount, moving the start of each cycle forward or backwards in time, so that it is out of phase with the clock.
Asynchronous mode provides a more traditional, free-running oscillator. Use the Async Rate knob to control the oscillation rate (frequency). The asynchronous LFO rate is specified in Hz.
Envelope Followers (Input Follower (In Fol.), Side Chain follower (S.C. Fol.))
Each input – the main audio input and the side chain audio input - has an envelope follower that is available as a modulation source in the In Fol. and S.C. Fol. columns on the modulation mixer.
The envelope tracks the overall amplitude of the input signal. This can be used to impart the amplitude profile of one sound onto another, for example. Each envelope follower has a Smoothing parameter (knobs located at the top of the Property Editor) that controls how rapidly the envelope follower tracks the input signal.
Relevant Example Files
The following files provide some examples of how SouthPole can be used:
GrungeDrumOne.amh, HappyPenguins.amh, SidechainingSouthPole.amh, SimplePlugnPlay.amh, MetaSSpatosaurus.amh & StayingSane.amh
To open the Example Files directory, go to the File menu, select Open, and double-click on the Examples folder. Read descriptions of the example files here.
The name SouthPole was a logical choice given that the contraption was inspired by NorthPole, a free plugin from Prosoniq. While the GUIs of the two contraptions are rather different, the basic idea is the same: a resonant low-pass filter with some modulation sources. Actually, NorthPole also includes a delay effect; you could easily add that in AudioMulch with a separate SDelay contraption.