The ES22 is a unique ten-band filter designed specifically for electronic sound synthesis and processing. Except for the top and bottom frequency bands, all other bands are spaced at an interval of a major seventh. This non-standard spacing avoids the very common effect of an accentuated resonance in one key, as will be the effect from graphic equalizers with octave or third-octave spacing between bands. Spacing by octaves will reinforce regular overtone formants accentuating a particular tonality. The ES22's band spacings are much more interesting, producing formant peaks and valleys that are similar to those in acoustic instrument sounds.
There are three equalized outputs, two of which mix the alternate filter bands, and one which is a mix of all filter bands. The UPPER COMB lets pass the outputs of frequency bands 61Hz. 218Hz, 777Hz, 2.8kHz and 11kHz. The LOWER COMB mixes the bands 29Hz, 115Hz, 411Hz, 1.5kHz and 5.2kHz. The LOWER and UPPER combs are not totally independent and there will be interaction between the 2 comb outputs.
This equalizer is different from other equalizers in that bands can be set to resonant. When the knobs are in the middle position, the response at the ALL OUT output is flat. When the knobs are positioned between -3 and +3, up to 2dB of boost or cut is set at the band. If the knob is set below the -3 position, the band will become resonant, simulating the natural resonance of acoustic instrument formant structures. Above the +3 position, increased band rejection is achieved.