THE FILTER

1. Frequency flier

Scot Solida looks into that most important of shapers

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Cherry Audio’s Voltage Modular Nucleus doesn’t give us a lot of choice when it comes to filters – there’s only one such module in the collection. However, it has all the features one might need for most uses. Go ahead and fire up Nucleus and click the New button in the upper-left to clear the rack. 4

Finally, bring in an Envelope Generator and drag it over to the left of your Amplifier. This will allow you to trigger sounds. Let’s begin patching. First, patch the Amplifier’s ‘+’ Output to the Oscilloscope’s Input A jack. Run a second cable from the Amplifier’s ‘+’ Output to the 1L(M) jack in the Main Outs panel up top. 2

To better understand what you hear – and see – you can build a simple synthesiser patch. Start by going to the module library on the left and scrolling down to the Oscillator module. Add it to your rack. Scroll up to the Filter and add that one. Don’t patch them together yet – we’ll get to that soon enough. 5

Go to the CV Sources panel up top and run a cable from the Gate down to the Envelope Generator’s Gate In jack. We can now trigger the envelope with MIDI. Patch the Envelope’s positive output (on the right) to the Amplifier’s CV Amount. Patch the CV Source’s Pitch to the Oscillator’s Pitch CV jack. 3

Next, scroll up in the Library until you see the Amplifier. Again, we’re not quite ready to begin patching. There are still two more modules to bring in. The first is an Oscilloscope. This will allow you to see the signal as you experiment with the Filter. Find that module and add it to your rack. 6

Each of our Oscillators’ outputs produces a different waveform, and all but the two on the left have different harmonics. Let’s run a cable from the bottom-left output to the Filter’s Audio In jack. Next, we’ll run a cable from the Filter’s low-pass output (the leftmost one) to the Amplifier’s Input.

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Go ahead and trigger a note – any note – from your MIDI controller. You will hear the Oscillator’s ramp waveform. You’ll also see its shape depicted in the Oscilloscope’s display. Currently, the Filter is not affecting it in any way. Find the Filter’s Cutoff knob. Play and hold a note, slowly turning that knob anti-clockwise.

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Let’s return to the low-pass output. Set your Cutoff to around 400Hz. Play and hold a note while paying attention to its sound and shape. While holding the note, switch the Filter’s Slope from 24dB over to 12dB. The Slope determines how aggressively the filter works on the harmonics immediately surrounding the selected cutoff frequency.

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You’ll note that the sound becomes less bright as you reduce the Filter’s Cutoff. If you look to the Oscilloscope, you’ll see that it also slowly loses its shape until it becomes a sine wave and then… silence. Try switching to the Filter’s other outputs and see how they affect your ramp waveform.

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Go back to your 24dB Slope. Now, set your Cutoff to around halfway. Find the Filter’s Resonance knob and play and hold a note. Examine the waveform as you gradually increase the Resonance knob until it’s set fully clockwise. Resonance (also called ‘Q’ or ‘emphasis’) boosts the level of the currently selected cutoff frequency.

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Using the low-pass output (the leftmost output), reducing the Cutoff reduces the high frequencies, allowing low frequencies to pass through. The highpass (rightmost output) does the reverse – it allows the highs to pass, filtering out low frequencies. The band-pass (middle) filters anything lower or higher than the Cutoff’s currently dialled-in frequency.

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Turn Resonance back down and the Cutoff fully up. Switch the Osc’s output to the sine wave (second from right). Play a note and turn the Cutoff. It doesn’t do a lot. That’s because it has nothing to grab hold of – the sine wave has no harmonics – only the fundamental frequency. Keep experimenting until next issue when we take a deeper look at filters.