Freakier Firmware

The analog filter: Cutoff, Resonance and Type

Open and close the filter, sharpen it with Resonance, and switch between low-pass, band-pass and high-pass.

Do it in the simulator ↗Lesson 6 · 4 min

The oscillator makes a bright sound full of overtones (the high frequencies that make a sound bright), and the filter takes some away. The MicroFreak's filter is a real analog circuit that comes after the digital oscillator. It is a gentle 12 dB-per-octave filter: it fades frequencies out gradually and does not chop them off. Cutoff is where it starts to cut, and Resonance boosts the sound around that point.

  • What a filter does to a sound and why Cutoff is the knob you will use most
  • What Resonance adds and when it starts to whistle
  • How low-pass, band-pass and high-pass differ
  • That the filter is analog while the oscillator is digital
The steps7 steps
  1. Hold a note and turn Cutoff down. The sound gets duller as the filter closes. This is a low-pass filter (check that the LPF light next to the Type button is lit): it lets lows through.
    Stuck?

    Hold a key and drag the Cutoff knob counter-clockwise (down).

  2. Now open it: turn Cutoff all the way up. Everything the oscillator makes comes through.
    Stuck?

    Turn Cutoff clockwise to the top.

  3. Sweep it back and forth a few times while the note rings. This is the most useful move on any synth.
    Stuck?

    Keep holding the key and move Cutoff up and down.

  4. Turn Resonance up. It boosts the sound right at the cutoff. Sweep Cutoff again and you will hear a whistle follow it.
    Stuck?

    Turn Resonance above the middle, then move Cutoff.

  5. Press the Filter Type button once. It is now band-pass: only a slice around the cutoff is heard.
    Stuck?

    Press the Type button in the filter section.

  6. Press it again for high-pass: it cuts the lows and keeps the highs. Sweep Cutoff to hear the bass leave.
    Stuck?

    One more press of Filter Type.

  7. Once more to return to low-pass. Turn Resonance back down, then play a note: the filter is back to where you started.
    Stuck?

    Press Filter Type once, then turn Resonance down.

Cutoff for brightness, Resonance for emphasis, Type for what is removed. Moving the cutoff while a note plays is the oldest synth sound there is.

On the real MicroFreak

Cutoff goes from about 30 Hz to over 15 kHz. With the filter in high-pass and Cutoff at the top there is nothing left to hear. Resonance can push the filter into self-oscillation, where it whistles a pure sine on its own. Cutoff is one of the matrix destinations, and Resonance can be assigned as one.

Questions2

Why does the sound disappear when I turn Cutoff all the way down?

In low-pass, which most sounds use, a closed filter lets only the lowest frequencies through, so the sound becomes dull and then quiet. Turn Cutoff up to let it back in.

What is the difference between 12 dB and 24 dB filters?

The number is how steeply the filter cuts above the cutoff. 12 dB per octave is gentler than 24, so the MicroFreak's sound opens up more gradually and stays a little brighter at the same setting.