Equalization / Equalisation (EQ)

Background

380_sudio_spectrum_2Use EQ to assist in the production of a quality recording, without changing the fundamental quality of the sound. This is good recording practice.

The term ‘Equalization’ or ‘Equalisation’, abbreviated as EQ, comes from the original intent of the invention – to make the recorded sound match the original source. EQ units are essentially a collection of frequency filters, often of different types, that provide the ability to reduce (attenuate) or boost (amplify) the signal strength of selected frequency bandwidths within a source signal. EQ is used to make up for inadequacies in the equipment and the recording environment, but it can also be used as a deliberate effect.

EQ types

There are various different EQ types:

 

Fixed Frequency

This is an Equalizer that operates at one or more specified frequencies, allowing the engineer to apply boost or cut at the specified frequency.

 

Graphic

This is an equalizer that operates on a number of fixed, preset frequencies. Any of these frequencies can be boosted or cut independently of the other frequencies. Graphic equalisers are normally composed of peaking type equalisers.

 

Paragraphic

This is a special type of Graphic Equaliser that allows the adjustment of the center frequency of each band to be adjusted by the engineer. Some also provide the ability to adjust the 'Q' or bandwidth of each filter.

 

Parametric

This is an equalizer that has a continuously variable center frequency, over a given frequency range. The 'Q' is also adjustable. If the 'Q' is not adjustable, the EQ is described as 'Sweepable', 'Tunable' or 'Quasi-parametric'.

 

Peaking

This kind of equalizer allows boost or cut to be applied to a source signal, using a bell shaped response curve. The Q setting determines the width of the bell while boost or cut determine the height or depth of the bell.

 

Shelving

This type of equalizer applieds boost or cut evenly to all frequencies beyond a threshold frequency using a shelf shaped response curve.

 

Sweepable

This kind of equalizer has a variable center frequency bu the 'Q' remains fixed.

 

Three Band

This kind of equalizer provides three separate frequency ranges that can be boosted or cut at the same time. Usually these are divided into low, mid, and high frequency ranges.

 

Two Band

This kind of equalizer provides two separate frequency ranges that can be boosted or cut at the same time. Usually these are assigned low and high frequency ranges.

 

EQ Techniques When Recording

 

Working with EQ

Generally, try and work quickly. Don't spend too much time on any one problem as changes you make as you progress through the mix could solve the problem anyway. It is improtant to remember that it is not each sound in isolation that is important, but the perception of each sound as part of the overall mix. Spending a lot of time getting a sound perfect on its own can be wasted effort as the changes you make may not be audible when the sound is combined with others as part of a mix.

 

Noise Reduction

The purpose is to obtain the best recording possible. When noise can't be removed by other means EQ may be able to sort it out.

 

Low Frequency Rumbles

Sensitive high quality microphones can pick up low frequency noise like traffic or household appliances air conditioning or heating systems. These sounds can be almost undetectable when using nearfield monitors, like Yamaha NS 10s.

Whenever it is possible listen to the input signal initially using large main monitors. Once you are satisfied that the effect of low level rumbles has been minimised you can continue using nearfield monitors.

To use EQ to address the problem use the low frequency roll-off filter on either your mixing console or, if it has one, the microphone. This should not effect the overall tonal quality of the sound unless you are recording something that contains a great deal of low frequency sounds like a bass or cello.

 

Mains Hum

Mains hum normally contains far more than just the obvious 50hz hum. It also contains some audible harmonics. To minimise any mains hum effects:

  1. Keep unbalanced cables as short as you can
  2. Don't use fluorescent lighting
  3. Keep Computer monitors away from your audio cables
  4. Don't use dimmer switches
  5. Separate your mains cables from your audio cables and keep them apart!
  6. Instead of standard guitar cables use guitar DI boxes and balanced mike leads

 

Hiss

Hiss is a common problem, especially when you are layering tracks in a multi-track recording. This is primarily because the individual tracks each contain an element of high frequency hiss. The best way to manage hiss is to remove it whenever you can from each individual tracks. For bass instruments, noisy guitars and electric pianos try applying a low pass filter at about 8 kHz. Otherwise use noise gates to suppress signals and therefor reduce hiss.

 

Interference

Unwanted interference has ruined many takes. When this occurs you can try filtering the high frequency content of the signal. Applying cut to the signal, lower the roll-off frequency until the sound appears muffled. Now raise the roll off frequency until the essence of the sound appears unaffected. It will reduce high frequency content but at least it should reduce any spillage from radio sources.

 

Noise Spillage

This comes down to learning from experience. You will need to learn the characteristics of different types of microphones and where and when to use them. The fundamental guides to microphone usage are the sensitivity and polar pattern of the microphone.

Knowledge of the recording environment is also essential to the management of noise spill. Removing noisy equipment to a separate area or room and placement of acoustic screens within the recording environment are both useful in reducing the spill from unwanted sources. Screens however can have a detrimental effect on the performance, as it will interfere with any visual communication between performers. Use of too much damping can result in a flat and lifeless recording. Careful application of EQ and a prudent use of acoustics screens can, in combination, resolve the dilemma.

When separating musicians in an attempt to manage spill you will need to be wary of introducing a slap-back echo of each instrument. The resulting sound will be full of echoes and will appear distant. Obviously these kinds of problems cannot be rectified using EQ!

 

Unwanted Harmonics

When recording real instruments unwanted harmonics can cause a ringing sound. Percussive instruments, particularly snare drums, often suffer from this problem. Other instruments can and do suffer from this problem, for example, even when an instrument is played evenly some notes may seem especially loud. Any number of sources can cause unwanted harmonics within the recording environment itself from speaker cabinets, furnishings, to the physical shape of the room. These kinds of issues are best addressed by physical changes to the environment. To reduce the occurrence or severity of unwanted harmonics, using EQ, use either a parametric EQ or a sweepable EQ with a very narrow bandwidth (Q). The EQ on budget mixing consoles is liable to use to broad a bandwidth to be effective. Instead, use a dedicated outboard EQ unit that has a good adjustable Q control.

 

Identifying a frequency

Firstly, be careful! Turn down the volume before you start so that the sound coming from your monitors is pretty quiet. If you don't you run the risk of damaging both your ears and your monitors. Set the Q to a very narrow bandwidth and set the boost to between + 6dB and +12dB. Using the EQ frequency control to sweep the frequency range in question. When you get to the correct frequency it will be obvious because of the jump in volume. Once you have identified the problem frequency change the boost to a cut of -6dB. Set the overall volume back to normal listening. While listening to the track adjust the amount of cut so that the track sounds balanced. Finally, change the Q setting to broaden the affected frequency to achieve a smoother more natural sound. This is unlikely to remove the ringing entirely but it should significantly improve the problem. Be prepared, though, there could be more than one unwanted ringing harmonic.

 

Adding Harmonics

You can also create new harmonics by boosting frequencies in a narrow bandwidth. For example: if a bass drum is sounding dull, try boosting a narrow band of frequencies in the 3 - 4kHz range to get more of a kick to the sound.

 

Flat Frequency Response

If you use a cardoid microphone for close miking you will encounter a colouration of the original sound, called "The Proximity Effect". This means that the bass response of the microphone is exaggerated resulting in a boomy sound. You could move the microphone further away from the source or use an omni-directional microphone but these solutions don't address all situations, for example miking drums. Using EQ you can of course cut some of the bass to make the drums sound more natural. To capture the sound of a drum kit make sure you compare the sound of the real kit with the sound that you hear from monitors. To achieve something that sounds comparable you are likely to need to use both a low frequency shelving EQ and some low frequency roll-off. Drummers can be very particular about the sound of their kit and, after all, it is an essential part of re-creating the sound of the band.

 

Improving the Sound

Avoid any temptation into applying unnecessary EQ during the track-laying phase of the recording. Leave this kind of EQ until all the tracks have been recorded. At this point you should have some idea about how the various tracks will sit in the mix. This means that your EQing will be informed and you will be more likely to get a track sound that fits well in the mix. If you must tinker with the EQ for no other reason than enhancement, be subtle. Use a broad bandwidth and only make small adjustments to bass, mid and treble frequency ranges. Don't roll off the extremities of frequency for any given track unless you are sure you won't need it later in the recording process. Once done it is very difficult to bring these frequencies back. You can always apply the EQ to just the monitor mix and leave you options open.

 

Analog or Analogue

Avoid cutting the high frequencies too much if you are using an analogue tape multi-track because if you need to boost these frequencies later you will most likely add hiss, even if you use noise reduction. Analog tapes also lose high end frequencies when you use them, so it is often a good idea to keep as much of the original high end content as you can. If there are rhythm guitars or any other sharp guitar sounds in the arrangement it can be worthwhile boosting the signal a little between 4 and 8 kHz at mix-down. This should compensate for any losses at the high end as a result of the recording process.

 

Digital

The high frequencies should be approached similarly in the digital domain. This is primarily because of the poor D to A converters on most budget digital systems. These tend to add significant hiss when a lot of high-end boost is applied. General Be careful, if you make a mistake during the track laying process you may not be able to fix the problem later in the engineering process.

Discuss this article in our Music Forum.

 

John Moxey

Site Crew

 

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