Equalizer

Equalizer, or EQ is sophisticated frequency control, which allow you to boost or minimize a range of frequencies, At its simplest, an equalizer divides audio signals into low, mid, and high frequencies. For example, you could increase the gain on the bass (the low frequencies) in your favorite dance music.

A common type of equalizer is the 1/3 octave equalizer, sometimes called a graphic equalizer. The graphic equalizer has 31 control points over the 10 octave to raise and lower the gain of the center frequency labeled above the control.

Limiter

Limiter are the same as compressor except that signals exceeding the threshold level are reduced at ratios of 10:1 or greater. Limiter can be set to prevent all signal from going above the given amplitude. Prevent the audio signal from being too intense, causing distortion or damage to the loudspeakers.

An example showing the use of a limiter:
The sound of a dropped microphone may be too intense, and cause damage to the audio system's loudspeaker.

Compressor

Compressor control the overall amplitude of a signal by reducing that part of the signal which exceeds an adjustable level (threshold) se by the user. When the signal exceeds the threshold level, the overall amplitude is reduced by a ratio, also usually adjustable by the user. For example, if the ratio of compression is set for 2:1, any part of the signal exceeding the threshold level is reduced by one-half. Compressor are used for reducing the overall dynamic range between the loudest and quietest signals. Compressor has ratio settings that are typically anything above 1:1 up to 10:1

Audio Signal Distortion

In any part of a system (amplifier, equalizer, cable, etc), there is an ideal, expected output signal waveform. Any false reproduction of audio is considered signal distortion.

The most common example of distortion occurs in analog equipment when the capabilities of the gear that receives of delivers the signal are exceeded. The amplitude of a signal must fall in a certain range to be accurately received by the device. The better quality the device, the more accurately it will handle the signal (less distortion).

The original signal is beyond the threshold, so the resulting signal is squared off.

If the amplitude of the sugnal is too low or to high for the device, it may be less inteleligible because of signal distrortion. The distorted sound is actually the odd harmonics of the signal being amplified and then added back into the signal.

Manufacturers generally specifify their product to be within a certain allowable tolerance of total harmonic distortion (THD). THD is generally given as a small percentage of the total signal, and measured at the maximum specifies output of the device.

Telephone conversations, not known for their audio quality, generally tolerate up to 10 percent distortion. In professional AV systems, a 1 pecent THD is noticeable to most.

It is up to the AV systems professional to assure that the installed system adheres to this tolerance by assuring the system is designed, set up and adjusted so that each item of equipment is getting and delifering the signal levels within the limits stated by the manufactures.