Previously we defined what an Equalizer is, in regards to audio. Now we’ll be talking about different methods of implementation for this process.

By definition, EQ’s are filters, and that is one of their most important uses. “Muddiness” is a common term used to describe when a mix is unintelligible due to the presence of too many overlapping low frequencies. Cutting out excessive low frequencies with a High-Pass (or Low-Cut) EQ, and reducing overly-resonant frequencies across your tracks is a good step on the path towards clarity in your mix. In some cases, it is necessary to remove other unwanted sounds from a recording too, like wind.



EQ’s can also be used to remove annoying hisses or high pitched ringing, like old CRT TV’s used to emit, by using a notch filter to cut the problematic frequency.



By using a shelving or a wide bell-curved EQ, you could also bring out different sonic characteristics in your tracks, like giving the bass more presence by boosting the low frequencies (20-120 Hz), or making them more “airy” by boosting the highest frequencies (5000 – 20,000 Hz).



EQ also has fun sound-design applications as well. For example, by using High-Pass and Low-Pass EQ curves together and narrowing the frequency bandwidth of your mix, you can get a cool “Classic Radio” effect. And by cutting only the high frequencies, you can fake the sound of somebody being behind a wall or far away (though sometimes it is better to simply record the real thing!).



These same principles can be applied creatively to add effects or to add depth to your music mixes. In the next example, I’ve simply taken the sound of a moving river and applied the aforementioned “Radio Effect” to get an underwater sound effect.



Another thing to keep in mind about EQ’s is that there is no need to keep them stationary. EQ’s can be automated and moved around just like many other effects. Sweeping (or moving steadily in one direction) a Low-Pass EQ’s is a very common effect in electronic music. You have most likely heard this effect to cause tension before “the beat drops”.



Many synthesizers will also allow you to bind different EQ’s to an LFO, or Low-Frequency Oscillator, to allow it to move independently with the synth. Even subtle EQ modulation on the LFO can give more life and variety to an ordinary synth sound.



As you can see, EQ is an incredibly versatile audio effect, and should be learned and explored by every budding audio professional.

Glossary: EQ Terminology

BAND – b) A range of frequencies, often identified by the center frequency of the range.

BAND WIDTH (Q) – b) Stands for “Quality Factor,” defining the bandwidth of frequencies that will be affected by an equalizer. The lower the Q, the broader the bandwidth curve of frequencies that will be boosted or cut.

BAND PASS FILTER – a) reduces both high and low frequencies, leaving a middle band of frequencies unaffected.
b) A device, circuit or plug-in that allows a narrow band of frequencies to pass through the circuit, rejecting or attenuating frequencies that are either higher or lower than the specified range.

BELL EQ – a) boosts or cuts energy with a peaked response.

CENTRE FREQUENCY – a) the point on the frequency spectrum where boost or attenuation is applied.
b) The frequency of an audio signal that is most affected by an equalizer, either boosting or attenuating the frequency. Drawn graphically, this is the very top or bottom (the “peak”) of the frequency bell-shaped curve.

GAIN – a) the amount of boost or cut applied to the centre frequency (measured in dB).

HIGH PASS FILTER – a) reduces low frequencies, leaving high frequencies unaffected.

LOW PASS FILTER – a) reduces high frequencies, leaving low frequencies unaffected.

NOTCH FILTER – a) cuts a very narrow range of frequencies.

SHELF EQ – a) boosts or cuts energy at the centre frequency and all frequencies above (high frequency shelf) or below (low frequency shelf).

Low-Frequency Oscillator (LFO) – b) A circuit that emits low-frequency electronic waveforms below the audible level of human hearing (20 Hz or less). This low-frequency waveform creates a rhythmic pulse that is used to modulate various parameters in the audio signal, such as pitch or volume. LFOs are frequently used in samplers, synthesizers and signal processors to create such effects as vibrato, tremolo, and phasing.

Modulation – b) Refers to any process in which a parameter of one signal is systematically affected by the introduction of another signal. In audio, this results in a change in the sound.

Source: a) Glossary b) Glossary

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