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The Orban/Parasound 621 Parametric Equalizer represents a significant price/performance breakthrough in the professional audio Equalizer field. The 621 uses a proprietary Orban/Parasound circuit to provide the user with continuously variable control of the three parameters of equalization: frequency of maximum equalization, bandwidth, and amount of peaking or dipping. Each channel of the 621 provides four such equalization sections connected in series, so that the total equalA sophisticated "peak-stretching" overload indicator circuit continuously monitors the output of each section, and flashes a front-panel LED overload indicator for 1/2 second if peak clipping occurs at the output of any section. Approximately 12 dB of gain is available, as well as an input level control. Thus the 621 can be used to make up gain, or to interface medium-level circuits with line-level circuits. The input level control also permits instant and straightforward correction of overloads. Each section of the 621 tunes over a 20:1 (4.3 octave) frequency range. For versatility, the frequency coverages of the various sections overlap widely. The equalization control permits a maximum boost of 16 dB, and a maximum dip of minus infinity. This notching provision permits the 621 to be used to remove hum or other fixed-pitch interference with negligible effect on the sound quality. In sound-reinforcement applications, it permits extremely easy removal of major ring modes. The use of "active R-C" circuitry means that the 621 is resistant to magnetically induced hum. Overload-to-noise ratio is typically 106 dB, and harmonic distortion at most frequencies and output levels is less than 0.03%. The 621 is an ideal replacement for any kind of Equalizer currently used in professional sound, with the exception of l/3-octave types used for "room tuning". The 621 can even do a surprisingly effective job in that application, partcularly if a dual-channel 62IB is used, with one channel notching the four major ring modes and the other channel providing broadband equalization.