Contents

Shaping Sound with Filters

Filters remove or emphasize certain frequencies. A raw saw or square is harmonically dense — bright, buzzy, hard to listen to for long. A filter is how you carve that into a tone that sits in a mix.

Your first lowpass filter

The lowpass filter (lp) is the most common. It passes low frequencies and cuts high ones:

// Raw sawtooth - bright and buzzy
saw(110) |> out(@)
// Filtered sawtooth - warmer and darker
saw(110)
    |> lp(@, 800)
    |> out(@)

The 800 is the cutoff frequency: frequencies above this get quieter.

The pipe and hole pattern

|> lp(@, 800) reads: pipe the saw into lp, drop it into the @ slot, set cutoff to 800. Every effect in Akkado uses the same shape — pipe in, name the hole, pass parameters.

Moving the cutoff

Lower cutoffs sound darker. Higher cutoffs sound brighter:

// Very dark - cutoff at 200 Hz
saw(110)
    |> lp(@, 200)
    |> out(@)
// Bright - cutoff at 2000 Hz
saw(110)
    |> lp(@, 2000)
    |> out(@)

Adding resonance

The third parameter adds resonance, a boost at the cutoff frequency:

// Q of 0.707 (default) - no resonance
saw(110)
    |> lp(@, 800, 0.707)
    |> out(@)
// Q of 4 - noticeable peak
saw(110)
    |> lp(@, 800, 4)
    |> out(@)
// Q of 10 - strong resonance
saw(110)
    |> lp(@, 800, 10)
    |> out(@)

Filter sweeps

Modulate the cutoff with an LFO for the classic synth sweep:

// Slow sweep using an LFO
saw(110)
    |> lp(@, 400 + sine(0.5) * 800)
    |> out(@)

The cutoff moves between 400 and 1200 Hz following a sine wave.

Envelope-controlled filter

For percussive sounds, use an envelope to control the filter:

// Filter opens on each trigger, then closes
saw(110)
    |> lp(@, 200 + ar(trigger(2)) * 2000)
    |> out(@)

Highpass filter

The highpass (hp) does the opposite: it removes low frequencies:

// Remove the bass
saw(110)
    |> hp(@, 500)
    |> out(@)

Useful for hi-hats and thinning out sounds:

// Hi-hat from filtered noise
noise()
    |> hp(@, 8000)
    * ar(trigger(8), 0.001, 0.05)
    |> out(@)

The Moog filter

The Moog ladder is the classic 24-dB analog filter — fatter than lp, with characteristic resonance:

// Classic Moog bass
saw(55)
    |> moog(@, 400, 2)
    |> out(@)
// Self-oscillating filter - acts as an oscillator
noise() * 0.01
    |> moog(@, 440, 3.9)
    |> out(@)

Chaining filters

Multiple filters in series:

// Remove lows and highs
saw(110)
    |> hp(@, 200)
    |> lp(@, 2000)
    |> out(@)

Next steps