Yamaha P-2200 Owner's Manual - Page 44
Parametric Equalizers, Other Equalizers, Equalizer Problems
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medium. At the same time, the studio monitors or audience foldback system might require graphic equalization to suit very different ends. Professional graphic equalizers are usually more durable than hi-fi type units, and they operate at nominal +4dB (1.23 volts) line levels. The input of a hi-fi type graphic equalizer will probably require padding for use with professional type mixers such as the Yamaha PMMixers, and its output level may be too low to drive some common power amplifiers (the P-2200's sensitivity is high enough to allow it to be driven by most hi-fi type graphic equalizers). Aside from level and impedance criteria, some graphic equalizers have characteristics that cause the overall response curve to change drastically when one frequency band is adjusted, so two or more bands must be adjusted to preserve a smooth response. Other equalizers maintain a smooth transition to adjacent bands when just one control is adjusted. Parametric Equalizers A parametric equalizer is one whose "parameters" can be varied to suit the application. The parameters include such factors as filter bandwidth ("Q"), center frequency, and amount of boost or cut. Usually there are several filters, and some "parametrics" are set up for stereo operation. Each filter section in the equalizer can either cut or boost frequencies within its band, and the ranges of center frequencies available from adjacent filters usually overlap. pedals," "phasers," "flangers," etc. Each of these devices was designed for a special purpose. Fig. 69 - Actions of Tone Controls High pass and low pass filters are special purpose devices. They are sometimes called "horizontal" filters because they do not boost or cut in the same manner as a graphic or parametric equalizer (which would be a "vertical" filter). High pass filters, which pass frequencies only above their "cut off" frequency, are used to cut low or subsonic frequencies from a sound system. Using a 40Hz or 80Hz high pass filter, for example, reduces dangerous dropped-mic, or turn-on, turn-off transients, etc., but allows all significant program frequencies to pass. A low pass filter, which passes frequencies only below its "cut off" frequency, can stop high frequency oscillations and certain RF interference from reaching the speakers. In commercial sound systems, high and low pass filters cut unneeded frequencies from the system, and thus increase the total capacity of the system to reproduce the frequencies of interest. Fig. 68 - Actions of a Parametric Equalizer By adjusting a filter for wide band rejection characteristics (low Q), it can perform room equalization in a similar manner to a graphic equalizer, or it can act as a variable frequency cut or boost tone control. In a narrow band reject mode (high Q), a parametric equalizer can be used for feedback control, or to notch out hum frequencies without subtracting much of the adjacent program material. Used carefully, a parametric equalizer can be an extremely helpful tool for sound reinforcement or for recording. It should be remembered that, like a graphic equalizer, excessive boost may reduce system headroom, create clipping and make extreme power demands on amplifiers and speakers. In addition, a parametric equalizer may "ring" at high-Q (narrow bandwidth) settings. Ringing is caused when a filter begins to act like an oscillator. While ringing may be useful as an effect, it may cause unwanted peaks in the system's frequency response curve. Other Equalizers Tone controls are another type of equalizer. So are a number of the special effects devices, like "wah-wah Fig. 70 - Actions of High and Low-Pass Filters Equalizer Problems The previous discussions illustrate some of the many uses of the various types of equalizers. Like any signal processing device, equalizers can also cause problems. From the power amplifier's viewpoint, the most significant problem that can be caused by an equalizer is clipping of frequencies that have been boosted to extremes. If these boosted frequencies are in the treble