Equalization is a fundamental processes in music production.
Every music producer should have various types of EQ in their arsenal.
These may be studio based or can be used in live performance rigs.
Equalizers are basically filters. They influence the volume of audio at specified frequencies.
Note that the audible frequency spectrum range lies between 20Hz and 20KHz.
There are many types of EQ. The most common are:
parametric, dynamic, graphic, and shelving.
Parametric Equalizers
Parametric EQs are the most common and I think the most flexible.
They take many shapes and forms. They can be a digital software plugin, can be part of a mixing console, or be a hardware device.
Parametric EQs all have common controls.
Frequency, Resonance or bandwidth (Q) , Gain, Filter type, Filter Slope.
(the left pic is of Abelton's EQ8)
Dynamic
These combine an equalizer with a compressor.
They can cut or boost frequencies depending on the amplitude of the signal at its input.
A traditional EQ is static. Dynamic EQ combines equalization with selective
compression/expansion and sidechain triggers. It kicks in only when the
signal you’re EQing goes above certain threshold which you pick.
Graphic Equalizers
These boost or attenuate a range of fixed frequencies using a bank of evenly spaced slider controls.
You can have up to 31 of these. The more sliders, the more accurate they are.
However, the frequencies are fixed and you have no control over the filter shape or bandwidth.
Shelving Equalizers.
These are very basic EQs which boost or attenuate frequencies above or below a specified cutoff point.
Most shelving equalizers have high and low shelving filters like in the Shelves module below.
Filter types & Slope:
The most common types are Bell, Bandpass, notch, High Shelf & Low Shelf.
We can also add High Cut & Low Cut to this list.
Abelton's EQ 8 is a great equalizer and a great way to explore these filter types.
EQ 8 has 8 parametric filters. Each filter can be one of 8 types.
This is a low cut or high pass filter
It passes all high frequencies above the cutoff point.
It's x4 meaning it is 4 pole
This is another low cut / HP filter
It has a gentiler slope than the previous one.
Use a low cut filter to remove low frequencies or automate the frequency to create sweeping effects.
This is a high cut filter. Also known as a Low Pass.
it passes all low frequencies below the cutoff point.
It's fun to automate the frequency to create sweeping effects.
This is another LP filter (or high cut)
The 4X indicates a Steeper slope than the previous filter.
This is a Notch filter. Also sometimes referred to as a Band Stop.
It attenuates and removes a range of frequencies around a specified
center frequency point. It will pass all the other frequencies unaltered.
Modulating notch filters creates interesting shaping effects.
It's the opposite of a bandpass filter.
This is a bandpass filter.
This has been made using a LP & HP filter.
Low and high frequencies outside the range are attenuated or cut..
Multiband equalizers often use multiple band pass filters to divide the audio spectrum into sections.
Here we have two bell filters. They are also known as peak filters. Use them to boost or reduce a range of frequencies with precision.
The bandwidth/resonance (Q) sets the width of the bell curve.
These are two shelf filters
On the left is a left shelf.
On the right we have a right shelf filter.
These are useful for boosting or reducing certain frequencies without totally cutting them out as you would have if you used a LP/HP filter combo.
You can make the filter slope less steep by dragging down the Q knob, or do the opposite by reducing gain.
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Enough theory.
Here are some of my favorite Equalizers
The Cwejman VCEQ-3
This is in Eurorack format.
The vceq-3 consists of 3 individual parametric equalizers.
the
frequency, bandwidth and amplitude can be controlled by dedicated knobs
and/or by external signals, individually for each band.
Serge Resonant Equalizer CGS
Serge Resonant EQ/Filter - Euro format (CGS 202)
It's a a comb filter based module. There is no CV control, but it has 10 bands of frequency to mix. The frequencies are fixed. It's closer to a Graphic Equalizer in design.
There is no control over the filter shape and bandwidth of each band.
Below is a pic of a vintage Serge Res equaliser.
It's the 3rd module from the left. It's very compact in comparison to the Euro version and doesn't have
the extra outs from the 10 filter bands. And pot's are used instead for sliders.
It's a really simple but beautiful module.
The 4 channel EQ has independent level, bandwidth and frequency controls that span a wide frequency spectrum from 20 Hz all the way up to 20 kHz.
Using the two outputs of this section, you can then patch signals to two
different modules for some extra modulation and waveform sculpting
possibilities and even switch between EQ’d and Bypass modes for a quick
comparison.
Mutable Instruments Shelves
4 Channels.
It's a mix of low-shelf, high-shelf, and parametric sections.
All share the same control ranges and scales
All channels have frequency & gain controls.
The middle two channels have resonance (q) controls.
These are the parametric sections.
The first band is a low-pass shelving filter & the fourth band a high-pass shelving filter
The good old Doepfer 128 filter bank.
(Fixed Filter Bank) is a filter bank,
made up of 15 parallel band pass filters, all with fixed middle frequencies and bandwidth
(50 Hz / 75Hz / 110Hz / 150Hz / 220Hz / 350Hz / 500Hz / 750Hz / 1.1kHz / 1.6kHz / 2.2kHz /
3.6kHz / 5.2kHz / 7.5kHz / 11 kHz).
Each band pass filter has its own amplitude control knob
If you want to add a single audio output for each
filter we have instructions for this modification available
L1 Quad VC Resonant EQ
4 channels of Parametric EQ
Also first band is switchable to LP mode and fourth band to HP to
make low and high shelves. Also each band is switchable to boost or cut
modes.
Every parameter has voltage control, also master CV ins for all bands
Trautonium Formant Filter
This was used in the Mixtur Trautonium by Oskar Sala. It is made of four parallel
resonance filters, each filter can be switched to low pass or band pass
or off.
There is no VC.
Frequency, Q & Vol are all manually controlled.
Its a graphic EQ
Music Thing Modular
A compact, clean seven band Eurorack graphic equaliser inspired
by the classic Boss GE-7 pedal.
