Resonance, slope and the classic types
Three controls turn a simple tone knob into an instrument. Resonance adds a singing peak at the cutoff, the slope decides how sharply the filter cuts, and the filter type decides which part of the sound you keep.
- Use resonance for focus, a vocal “wah” or a singing peak
- Hear the difference between 12 dB and 24 dB slopes
- Pick the right classic type: low-pass, high-pass, band-pass or notch
01Resonance: a peak at the edge
Turn up Resonance and the filter stops being a plain slope. It adds a peak exactly at the cutoff, boosting whichever harmonics sit there: the filter’s resonance.
At 0% the curve simply bends down. As you raise it, a bump grows at the cutoff, and the frequencies just below it get louder than the rest. The ear hears that as focus: the sound becomes more nasal, more vocal, more “synth”. Push it further and the peak starts to sing a pitch of its own at the cutoff frequency.
Resonance: a peak at the cutoff
Look at the bottom row. At 85% the waveform gains a fast ripple on every cycle. That ripple is the filter ringing at 1 kHz, the way a glass rings when you tap it. The higher the resonance, the longer the ring lasts.
Edit›Filter 1›Resonance runs from 0% to 90%, and the knob is not evenly spread. Up to about 60% it adds gentle focus: the peak never passes +1 dB. Above 60% it climbs quickly: +10 dB at 70%, +23 dB at 85%, +26 dB at 90%. Most musical settings live in the first two thirds; the last third is for singing, whistling peaks. Even at 90% the four classic types never run away into a howl: their ring always dies away. (Some of the other types do sing on their own, such as the Ladder: Module 6.)
Resonance and “Q” Deeper theory
Engineers describe a resonant filter by its Q, the sharpness of the peak. KiMiA’s Resonance 0% is a gentle Q of 0.5, where the curve is already 6 dB down at the cutoff. The Q rises slowly to 1.1 at 60%, then steeply: 3.3 at 70%, 14 at 85%, 20 at 90%. A filter with a Q of 20 boosts the cutoff frequency twenty times in amplitude, which is +26 dB. In 24 dB mode two filter sections run one after the other, and only the second takes the steep part of the resonance, so a 24 dB peak is about as tall as a 12 dB one.
02The resonant sweep: where “wah” comes from
A resonant peak really comes alive when it moves. As the cutoff sweeps down, the peak passes over each harmonic in turn and makes it flare up for a moment. Your ear follows that moving peak like a voice saying “weeoww”.
A resonant sweep: the peak lights up each harmonic in turn
This one effect is behind the talking basses of acid house, the “quack” of funky clavinets played through a wah, and the vowel-like shimmer of countless leads. In Lesson 5.4 you will make the cutoff move by itself, with every note you play.
High resonance boosts whatever sits at the cutoff. On bass notes with a low cutoff, the boosted frequency can be the fundamental itself, and at 85% that means a jump of more than 20 dB. When you raise resonance, play the lowest notes you will use and lower Level if they jump out.
03Slope: 12 dB or 24 dB
The slope is how quickly the filter turns harmonics down once they are above the cutoff. It is measured in decibels per octave. KiMiA’s filters have two:
- 12 dB: a gentle cut that leaves some buzz and edge. It suits brass, strings, organs and sounds that should stay open.
- 24 dB: twice as steep: rounder, darker, “fatter”, and sweeps sound more dramatic. It is the classic choice for basses, pads and anything that should be warm without fizz.
12 dB versus 24 dB at the same cutoff (700 Hz)
Notice how the two curves agree well below the cutoff and then part company. Right at the cutoff the 12 dB curve is already 6 dB down and the 24 dB curve 12 dB. At the same cutoff the 24 dB version always sounds darker, so after switching slope you will often raise the cutoff a little to get the brightness back.
04The four classic types
Filter 1›Type has nineteen buttons. The first four, LP, HP, BP and Notch, are the classic shapes every synthesizer shares, and each keeps a different part of the sound. The other fifteen are flavors: famous filter circuits and special shapes, each with a character of its own. They get Module 6; everything you learn here about cutoff, resonance and slope carries over to them.
The four classic types, one saw wave, cutoff at 1 kHz
Each type, swept
| Type | Keeps | Sounds | Reach for it when |
|---|---|---|---|
| Low-pass (LP) | Everything below the cutoff | Warm, dark, round | Almost always: it is the “brightness” filter behind most patches |
| High-pass (HP) | Everything above the cutoff | Thin, airy, light | A pad or string layer must not muddy your piano’s left hand, or you want a “small” sound |
| Band-pass (BP) | A slice around the cutoff | Nasal, telephone, radio | Lo-fi colors, vowel-like leads, wah effects when swept |
| Notch | Everything except a slice | Hollow, slightly phasey | Taking the honk out of a sound; swept slowly, it sounds like a phaser |
Pianists who layer a synth pad over an acoustic piano often high-pass the pad at 200–400 Hz. The pad then adds color to the right hand without thickening the bass register, where the piano is already full. Keep the strong low end for the bass part alone, and any two sounds will layer without turning to mud.
05Try it
- Hear resonance grow. Load 05 · Resonant Saw. Hold C3, set Cutoff to about 900 Hz and move Resonance from 0% to 90%. Notice how little changes until about 60%, and how fast it grows after. Then set Resonance to 80% and sweep the cutoff slowly: listen for the “wah”.
- Compare slopes. Set Resonance to 20% and Cutoff to 700 Hz. Switch Slope between 12 dB and 24 dB. Then find the 24 dB cutoff that sounds as bright as 12 dB at 700 Hz. It is usually noticeably higher.
- Walk through the types. Set Cutoff to 1 kHz and click LP, HP, BP and Notch in turn. Describe each in one word before you check the table above.