Akai S5000 Operator's Manual download pdf (Page 123)

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There is one further aspect to filters one has to consider, however, and that is ROLL-OFF.

You will see filters referred to as 1-POLE, 2-POLE or 4-POLE - maybe even 6-POLE. A ‘pole’ is

equal to 6dB of attenuation per octave. Thus, a 2-POLE filter offers 12dB/Octave roll-off whilst a 4-

POLE offers 24dB/Octave rolloff. A 6-POLE filter offers a theoretical 36dB/Octave roll-off but these

are unusual largely because the difference between 4- and 6-POLE is so subtle that it is largely

inaudible in a properly designed filter - most of the ‘classic’ analogue synthesisers only offered 2-

or 4-POLE filters (i.e. 12dB/Octave and 24dB/Octave roll-offs). You can see the difference between

a 2-POLE and a 4-POLE lowpass filter in the following diagram:

FREQUENCY

Cutoff

A 2-POLE or 12dB/Octave lowpass filter

FREQUENCY

Cutoff

A 4-POLE or 24dB/Octave lowpass filter

Although the cutoff frequencies in both diagrams are the same, the roll-off on the 4-POLE is slightly

steeper. The effect is that the 2-POLE filter is a little ‘fizzier’ sounding than the 4-POLE as extra

harmonics are passing through because its roll-off is less severe.

In the ‘good old days’ of analogue synths, some manufacturers used 2-pole filters, others used 4-

pole filters. Moog synthesisers had 4-pole filters and many people attribute the classic MiniMoog’s

punchy bass end to this (other factors are actually responsible as well, as it happens). Sequential

Circuit’s Prophet 5 and Pro-1 also used 4-pole filters.

However, Oberheim synths typically had 2-pole filters and yet no-one accuses them of lacking any

‘punch’! Some synths offered a switch to choose the cutoff frequency’s response slope.

The S6000 offers both options and a wealth of other filter types besides.

So, with the theory out of the way, let’s now look at the filters’ parameters.

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Akai S5000 Operator's Manual Page 123