Mastering EQ - Air Band Processing

How to process the Air Band using equalisation - add sparkle and space to your mixes.

Dynamic Processors

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Mastering EQ – Air Band Processing
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Mastering EQ – Air Band Processing video tutorial explains how to use an equaliser to process the elusive air band of a mix.

When using equalisation to master a stereo mix one area that can make or break your master is that of the crucial air band. Knowing how to process this area of the frequency spectrum involves understanding how to ‘listen’ and then taking appropriate equalisation decisions to best process it. One of the most powerful features an equaliser can offer is that of splitting frequency bands and then using panning techniques to spread the air band into a wide and more spacious texture.

But first, we must clean the audio using corrective equalisation.

Corrective or Compensatory eq

Actually the first ever instances of equalisation was in the communications industry. EQ was used to counteract some of the problems in telephone systems. It then transgressed into the broadcasting industry.

Tone controls were created and used to compensate technical inaccuracies in the recording chain, more notably, compensating for microphone colouration and room acoustics. EQ was used as a means of controlling the gain of a range of frequencies.

This form of equalisation is termed as ‘corrective or compensatory’ EQ.

We use the same principles when using equalisation to remove problematic or redundant frequencies and the filter type we use to perform corrective processing on any sound is band-pass equalisation.

Band-pass filtering

I always start by inserting hi pass and low pass filters at either end of the spectrum. In effect I am using band-pass filtering/equalisation.

linear phase versus minimum phase screen displaying an eq response

A filter that passes frequencies between two limits is known as a band-pass filter.

A band-pass filter attenuates frequencies below and above the cut-off and leaves the frequencies at the cut-off. It is, in effect, a low-pass and a hi-pass together. The cool thing about this filter is that you can eliminate the lower and higher frequencies and be left with a band of frequencies that you can then process without the worry of redundant frequencies creeping up on you and summing gains and tripping compressors.

A filter that adjusts the levels of frequencies between a pair of values is known as a peaking filter.

Once I have the two filters in place I start to move them around until I have cut all the frequencies not needed.

Once we have tidied up the frequency spectrum of the sound we can start to work on the airband.

Air Band

The air band is a range that loosely lies between 4 kHz – 20 kHz. This is the area of the spectrum that displays detail and clarity for the top end of many sounds. I find that using shelves to boost the air band range yields far better results than using peaking bell-shaped filters. However, you can make the bell filters work for you instead of against you as there are frequencies that are in the upper-frequency spectrum that we cannot hear so using a shelf to boost this particular area yields no usable results.

Splitting Bands

Some equalisers come with a function that I think is extremely powerful – that of splitting filter bands into two distinct copies (left and right) that can then be moved along the frequency spectrum. This is a great way to add width to an existing sound. Splitting and widening the airband can dramatically alter your mixes and I urge you to try this technique on all stereo sources.

In the Mastering EQ – Air Band Processing video I explain what band-pass equalisation is and how we use it to remove redundant frequencies. After the cleaning process, I show you, in detail, how to find the right frequencies to process and how to select the right slopes to ensure smooth transitions from band to band. Finally, I show you how to split the air band into two copies and pan each copy to achieve a wide spacious texture.

Plugins used in this video:

FabFilter Pro Q2

SSL Stereo Bus Compressor

Topics covered in this video are: