Filter slope steepness is measured in dB/octave; each pole adds 6 dB/oct of attenuation

A filter’s slope describes how quickly it attenuates frequencies beyond the cutoff point, measured in decibels per octave (dB/oct). Each filter pole contributes 6 dB/oct: a one-pole (6 dB/oct) filter barely attenuates harmonics; a two-pole (12 dB/oct) is more pronounced; a four-pole (24 dB/oct) is the most dramatic, producing the fat, closed sound of classic Moog and Roland filters. The 12 dB/oct filter appears in many vintage Arp, Korg, and Oberheim instruments; 24 dB/oct is associated with the Moog ladder filter. The slope choice affects the character of timbre change as a filter sweeps: gentle curves (6/12 dB) blend continuously; steeper curves (24 dB) create a dramatic opening/closing effect.

Examples

Moog-style 24 dB/oct LPF: dramatic, woody close. SEM-style 12 dB/oct: smoother, less dramatic but wide stereo character. A 6 dB/oct gentle roll-off barely changes tone — used for subtle EQ rather than synthesis.

Assessment

A harmonic lies 2 octaves above a filter’s cutoff. Calculate the attenuation at that harmonic for 6 dB/oct, 12 dB/oct, and 24 dB/oct slopes. Name one synthesizer associated with each of the 12 dB/oct and 24 dB/oct filter slopes.