Audio Control Richter Scale Series Three III Bass equalizer/analyzer electronic crossover

The Audio Control "Richter Scale" (henceforth referred to as the RS) is a special-purpose five-band graphic equalizer and wave analyzer that operates only at frequencies below about 200 Hz. Its filters, spaced at half-octave intervals, have center frequencies of 31.5, 45, 63, 90, and 125 Hz. Each slider control adjusts the gain in its own frequency band over a ± 12-dB range. Adjusting any graphic equalizer by ear can be difficult, and to simplify the process the RS contains a tunable warble-tone generator covering the range from 31.5 to 250 Hz. Its frequency is adjusted by a small front-panel knob whose calibration points correspond to the filter center frequencies (the 250-Hz point serves as a reference level to which the response at the other frequencies can be matched by use of the slider controls).