ELECTROMAGNETIC SPECTRUM & EQUALIZERS

Radio waves are a form of electromagnetic radiation: Electromagnetic radiation is the transmission of energy in the form of waves that have electrical and magnetic components. Where scientists once thought magnetism and electricity were entirely unlinked phenomena, research over the last few centuries proved beyond a doubt that not only were the two linked, in many cases they were simply different expressions of the same energy.
 
The most familiar forms of electromagnetic radiation are radio waves and visible light waves. They differ primarily only in the frequency and wavelength of the radiation.

All electromagnetic waves travel through empty space at the same velocity (speed) – namely the speed of light. The speed of light (often denoted by the symbol ‘c’) is 2,99,792,458 metres per second. For most calculations the approximate value of 3,00,000 km/s is used. This is true whether we are talking about radio waves or visible light.

Mathematically, electromagnetic waves are represented by sine waves. The sine wave is a graphical representation of wave phenomena. As we have seen earlier, the wavelength and frequency of any electromagnetic wave are related to one another inversely; that is, when one increases, the other decreases.
We can now quantify this as an equation as:

Wavelength = Speed of light / frequency
 
Different forms of electromagnetic radiation are characterized by their wavelength and frequency. When electromagnetic waves are ordered by frequency or wavelength, this ordered array is called the electromagnetic spectrum.
 
The electromagnetic spectrum represents all electromagnetic signals, from very low frequency (long wavelength) to very high frequency (low wavelength). Note that even visible light, the electromagnetic radiation that our eyes have evolved to perceive, is itself composed of a variety of frequencies of light: The colours of the rainbow that we see when sunlight is refracted or broken up by a glass prism are the different frequencies of light that together make up (white) sunlight.

EQUALIZERS

Many of us are already familiar with the treble and bass controls on our home stereos, that let us control whether the sound is higher or deeper in pitch.

Consumer grade equalization controls

The tone and bass controls are the most basic equalisers, allowing you to change the overall mix of frequencies in the audio to suit our listening experience, the listening area we are hearing the audio in - or to emphasize specific instruments or voices in the audio. Essentially, they act as a sort of electronic filter, allowing you to turn up certain frequencies in the audio, and turn down others.

A slightly more advanced version of the treble and bass knobs is the graphic equalizer, which is often found as a set of sliders on hi-fi consumer equipment. Each slider controls a specific band of frequencies, with the entire range from 50 Hz to 20000 Hz divided among 6 or 8 sliders. These are better than simple tone knobs or controls.

Professional grade equalizer controls

The equalizer controls on professional equipment are a lot more precise than the band equalisers found on home and consumer grade equipment. (Band equalizers are so named because they are not very precise, affecting a large group of frequencies together rather than a single frequency or a small range of frequencies.)
On studio mixers, one typically sees an equalization section that includes HI, MID and LO knobs, as well as an EQ button. Pressing the button activates the equalization section, and using the three knobs turns up or turns down the gain for the three equalization/filtration units.
 
The LO knob is a high-pass filter, which means it only low frequencies.

The HI knob is a low-pass filter, which means it cuts or boosts only high frequencies.

The MID knob is a bandpass equalizer. It typically affects frequencies between 500 Hz and 5000 Hz (the frequencies most commonly falling within the human vocal range). On many mixers the MID equalizer is also tunable, in that the centre frequency can be changed: This is the frequency in the exact middle of the range that this knob controls. This form of EQ is also known as a sweep equaliser.

Parametric equalization

The parametric EQ is very like the sweep equalizer in that it controls a band of frequencies. In addition, it has a third control that allows the width of the band to be adjusted. This is referred to as the ‘Q’ of the control: A higher Q means a wider band of frequencies is being controlled, and a lower Q means a smaller band of frequencies is being controlled.

Software based equalization

Many audio editing and processing software now include equalization sections where you can perform the same function, sometimes in an even more precise way. Often these softwares have graphical representations of the equalization controls, to make them comfortable for those used to hardware mixers.


Don’t use equalization when recording audio unless there is no other way. Most of the time, audio is poor only because our microphone position or recording area is not up to scratch. Use equalization only at the post-production stage – and in moderate amounts.