An equalizer is one of the most powerful tools available to us to modify, restructure and design sound by adjusting frequency responses.

The flat response

If you find this article useful, you may find the Article on Effective Equalization + compressor + reverb useful too.

Any sound equipment aims to have a flat frequency response, trying to preserve the balance of frequencies of the original signal in the same proportion at the output.

An audio equipment with a flat response will let out a vocal sound preserving its qualities – boomy, nasal, muddy, sizzling or pleasant – as it entered the equipment through the mic and preamp.

For example, a cymbal naturally has strong high frequencies, and that emphasis towards HF (high frequency) will be preserved by a flat response audio device. If an electric guitar is muddy, that sound will be preserved perfectly by an audio device with a flat response.

An EQ lets us change the flat response

The figure shows a state of the art Equalizer plugin interface by Waves.

eq-interface

Place an Eq in the signal chain and work with the parameters of an EQ to design sound by changing the frequency responses.

Vocals recorded with SM58

Shure SM58 is the most popular stage vocal mic. It can be used in budget recording situations to give decent results.

When you are mixing vocals recorded with the SM58, you want to make it sound good individually while making it fit in the mix.

Use an equalizer to work with the frequencies. Vocal recordings with an SM58 mic needs

  • cut in the bass frequency region
  • modification in the mid area
  • some work with the hi mid frequencies for clarity and intelligibility
  • and raise in the higher frequencies to give it the 'air'.

How to start using the equalizer?

How do we make the changes? To begin with, know the parts of an equalizer.

The Three Parts of an Equalizer

three-parts-equalizer-curve

There are three parameters we want to control:

Frequency

The frequency parameter is used to set the center frequency.

Once the center frequency is set, change the width of the frequency curve or change the gain keeping the frequency as the center.

We set the center frequency for each band of equalizer used.

For eg: we could have four bands with

  • one centre frequency at 200Hz
  • another at 2000 Hz
  • one more at 8000 Hz
  • and the last one at 16000 Hz.

The EQ band will have an option to change the Gain and Width at the particular center frequency.

Gain

We cut or boost the presence of a frequency using the Gain parameter.

Boost or cut according to the instrument and according to which characteristics you want to highlight.

We may cut down the vocals at around 600 Hz to reduce the muddy nature or room boom out of it. The mid frequencies can be carved away from the drum overhead mic tracks to reduce the clutter while using the highs.

Use the gain parameter to boost the 8000 Hz frequency in a SM58 vocal recording to increase the legibility of the recording.

Gain is the degree of boost, at the centre frequency (the frequency value that we set in the frequency parameter part). The gain is measured in decibels (dB),
A range of 12 to 15 db is maximum. The gain can be negative : -6db for example. Negative gain reduces the presence of a particular frequency.

Bandwidth Q

Bandwidth is a measure of the width of the bell-shaped curve. It is represented by the letter Q.

  • A lower Q (a Q value of 0.3 is low, for example) will allow the equalizing to cover a wide range of frequencies.
  • a higher Q (e.g. Q value of 5 or 7 is on the higher side) will allow you to home in on a particular feature of the sound.

Inverse relation: Q vs range

  • Lower the Q value, more the range of frequencies you affect with your gain change.
  • Higher the Q value, lesser bandwidth, less the range of frequencies affected.

Q is the extend – how wide or narrow the range of frequencies affected.

  • Lower Q – wider curve – more frequencies affected
  • Higher Q – narrow curve – less frequencies affected

When you want to remove a particular frequency with precision, use a high q, which makes the cut narrow.

When using additive equalization (boosting frequencies to make the change instead of cutting away unwanted), we need to be specific with the frequency so that the degradation of the original signal is kept to a minimum. So we choose a narrow band (higher Q value) when making additive frequency response changes.

Different kinds of equalization filters and curves

These are kinds of filters and curves available in equalizers

High pass filter

High pass filter section reduces low frequencies, allowing the higher frequencies to pass through.

For example, to cut away the bass frequencies in a vocal recording, use a high pass filter, which cuts off the lower frequencies.

You will be able to choose the frequency from where the cut is active, and the curve will slope down instead of an abrupt cut off.

Low pass filter

A filter section that reduces high frequencies, allowing the lower frequencies to pass through.

Band pass filter

A filter section that reduces both high and low frequencies. We adjust the Q, the center frequency and the gain to use band pass as needed.

Shelf

A high or low frequency EQ where the center frequency is selected and the bandwidth can be varied to extend the effect of the EQ to any frequency in the whole audio spectrum.

A shelving filter can be used anywhere in the frequency spectrum, to boost or gain a band width of frequencies.

Gain and Q parameters change the shape of the shelving curve as you need:

  • Choose the frequency
  • set the width Q
  • change the gain as needed.

Notch filter

A filter that cuts out a very narrow range of frequencies. We sweep (described below) and find out the frequencies and cut out the unwanted frequency with a very narrow band width. With this sort of precision, nearby frequencies are not disturbed while the sound is improved.

Peaking filter

A narrow band width filter that boosts a narrow range of frequencies.
All good equalizers will have the high pass, low pass and shelving or band pass filter.
Look at the shape of the curve when you choose each option and you will find what is best for the situation.

Parametric equalizers offer good control over all three EQ parameters. There are good parametric equalizer plugins with 2 to 10 number of equalizer bands. The first image of the equalizer interface is of the Renaissance EQ which comes with Waves Gold Bundle.

Get the complete short e-book Effective Equalization ($4.95). It is a 20 page downloadable pdf that starts you from the basics and then gives step by step best practices. It has sufficient density of information to keep a beginner practice for a few months at least. The information will form a good basis for all the equalization you will ever do. Emphasis given on Vocal EQ, SM58 vocals.

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