The Tangle Oscillator block is based on a type of synthesis called phase distortion. This form of synthesis takes a simple waveform like a sine wave (a simple waveform that produces a pure tone) and then bends, repeats and distorts the shape in various ways to produce more complex and rich waveforms. 3 of the knobs on the block: REPEAT, BEND and PW (PULSE WIDTH) use phase distortion to distort the waveform in various ways.
The REPEAT knob repeats the waveform so that multiple copies of it fit the space of a single waveform, this repeat function is only applied to the sine and cosine shapes (the cosine shape is the same as the sine shape except it starts at a different place in the waveform). The REPEAT knob creates lots of very high harmonics but as it’s only applied to the sine and cosine shapes it can be blended with the other shapes for more subtle effects. By finding these in-between shapes many complex waveforms can be produced.
For example, the waveform shape below is produced by using the SHAPE knob to blend the square waveform with the cosine waveform, the REPEAT knob is set so that the cosine waveform is repeated a bunch of times. As you can see, the repeated cosine waveform blended with the square creates a ripple effect on the top and bottom of the square shape:
The PW (PULSE WIDTH) knob bends the waveform shape to the left and right, squashing it up to one side or the other. It can sound similar to the pulse width control on an analog oscillator.
The BEND knob is similar to the PW knob except it bends the waveform inwards towards the middle or outwards towards the edge of the waveform, resulting in a different change in timbre.
FM (Frequency Modulation)
In addition to the 3 phase distortion knobs the blocks has an FM knob in the top left hand corner, this knob applies frequency modulation to the oscillator. Frequency modulation takes the signal from one source, for example from a separate oscillator connected to the FM input, and uses this signal to modulate the frequency or the phase of the oscillator. This form of synthesis, called ‘FM synthesis’ produces very rich and complex tones with lots of extra harmonics. If the pitch of the modulating signal and the pitch of the oscillator are different then metallic and dissonant tones can be produced. All of this, when combined with the block’s phase distortion functions can result in many interesting, harmonically rich sounds.
The FM knob sets the depth of frequency or phase modulation from the FM input port. If the FM input port is not connected then the FM knob will apply internal modulation, depending on the setting of the FM MODE control, either from a secondary internal oscillator or from the output of the oscillator itself (resulting in ‘FM feedback’).
FM Mode Switch
This switch below the FM Knob toggles between 6 different modes of modulation:
- PHASE (PHASE MODULATION) = Phase modulation (similar to FM hardware synths) where the ‘playback position’ of the waveform is modulated by the signal from the FM input port. If the FM input port is not connected then the output of the oscillator is feedback to the FM input instead, resulting in FM feedback, a technique that often results in quite noisy, raucous sounds.
- FREQ (FREQUENCY MODULATION) = Linear-through-zero frequency modulation. If the FM input port is not connected then in this mode a secondary internal sine-wave oscillator is connected to the FM input instead. In this mode the secondary oscillator is tuned an octave above the main oscillator.
- P RECT (PHASE RECTIFIED) = Same as PHASE except the modulating signal is rectified (negative part of the waveform made positive). This results in a different timbre than regular phase modulation. If the FM input port is not connected then in this mode the rectified output of the oscillator is feedback to the FM input instead, resulting in rectified FM feedback.
- F RECT (FREQUENCY RECTIFIED) = Same as FREQ except the modulating signal is rectified. If the FM input port is not connected then in this mode a secondary internal sine-wave oscillator is connected to the FM input instead. The secondary oscillator in this mode is tuned an octave below the main oscillator.
- FB (FEEDBACK) = The raw output of the oscillator is feedback, unmodified to the FM input. This feedback occurs within the oversampled engine resulting in a less noisy result than regular FM Feedback.
- S&H (SAMPLE & HOLD) = The oscillator's signal is sampled and then held at that value whenever the FM input is positive. If the FM input port is not connected then in this mode a secondary internal oscillator is connected to the FM input instead. The secondary oscillator in this mode is tuned 2 octaves below the main oscillator.
- HOLD = Similar to S&H except the oscillator signal is 'sampled and held' whenever the FM input is positive, and left unchanged when it's negative. If the FM input port is not connected then in this mode a secondary internal oscillator is connected to the FM input instead. The secondary oscillator in this mode is tuned 2 octaves below the main oscillator.
Finally the block features a LO-FI section that accurately models the behaviour of a variety of vintage digital circuits. Applying these lo-fi modes brings a completely different character to the oscillator.
Internally the oscillator uses a form of anti-aliasing called 'Infinite Linear Oversampling' developed by Efflam Le Bivic and Vadim Zavalishin. This from of anti-aliasing gives the oscillator a very clean, analog character and permits more extreme warping and distortion than would otherwise be possible.