All the cable connections in a modular synth represent the passing of voltages. We have already been using these, both audio and triggers are defined as a voltage and can be viewed on the Scope module.
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Voltages are used to control parameters, where you see a parameter with a Large knob, a small knob and an input jack grouped the parameter can be controlled by connecting a cable and turning the small attenuverter knob to adjust how much influence the control voltage has.
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In the above image, we have the top row where two signals are generated, the LFO, Low-Frequency Oscillator is producing a slow sinewave that we shall use as our control voltage (CV), as displayed in the blue plot on the top scope. The Wavetable oscillator is producing an audio signal, as shown in the red trace on the top scope module
On the second row, we have a Voltage Controlled Amplifier (VCA), the red cable carrying the audio signal is passed to the input. The blue cable's control voltage(CV) is connected to the level input on the VCA, and the attenuverter is turned fully clockwise. This is akin to the blue signal turning the volume control up and down. The result can be seen on the lower scope.
I highly encourage you to make this patch and experiment until you understand this concept, as voltage-controlled parameters and Control Voltages are fundamental to using a modular synth.
Pitch information
Pitch information as expected is very common in a modular patch, so common we always use a yellow cable. MooMu Modular uses a 1 Volt per Octave system, this is the same system as used in the popular Eurorack, and Kosmos formats. It is usually labelled V/Oct and will be labelled as such on the output of sequencers, and the input of sound generators.
So what does 1 Volt per octave mean, imagine an oscillator, with no input, that is tuned to a pitch, if it has hot been adjusted will be Middle C, C4, 261.63hz, if the input is increased by 1V it would be C5, set to -1V it would be C3. If you want to adjust the tunning by 1 semitone, it would be 1/12 Volts.
Now we know what V/Oct means we can put it to the back of our minds, this is a synth with knobs, we are not going to be getting our calculator out and typing in numbers, but more like the analogue hardware, turn a knob until it sounds right.
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Let's test this out. Make a patch to match the image above. The PTK module, Push, Moment, Knob, has some controls we can use, in this case, we want the bottom knob, marked Level, with the range set at its default, 1V, turning the knob will produce the range -1v to +1v. Turn the knob, and you will be able to see on the tuner the pitch, with the knob turned fully counterclockwise you will get C3, in the centre position C4, and fully clockwise, C5. Just like when you move your finger on a string, all pitches can be played, not just the notes.
We can add a quantizer to snap the pitch to selected notes. It is common if you come from a non-modular background to think of quantization as correcting timing, here it is correcting pitch. Imagine adding fretts to a single-stringed instrument, just on the notes you want to play.
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If we now add a quantizer to the patch as shown In the image above, and twist the bottom knob on the PTK module, you will see that the output snaps to the notes of the chromatic scale. The push buttons on the Quantizer module panel are arranged to mimic an octave on a keyboard. If we set the buttons to match that of a scale, C Major being just the white keys, and again turn the bottom knob on the PTK module, you will see just the notes of a major scale.
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Sequencing Notes
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Using our last patch, delete the PTK module, by selecting it, then in the toolbar, Edit, Erase.
From the Module Browser Tab, drag a Clock module, and a Seq Oct Cv module to the patch, as shown in the image above.
Using green cables, connect the 1/16 output of the Clock, to the Trigger input on the Seq Oct Cv module, and connect the resets between the same modules. Using a yellow cable, connect the Out of the Seq Oct Cv to the In of the quantize module.
Press run on the Clock, and turn the knobs on the Seq Oct Cv module, Congratulations you have just made your first melodic patch.