What is dynamic EQ?

Equalisation is the audio engineer's most widely used processing tool. However, the equalisation applied is usually static -- it remains the same over time.

This is often undesirable! For example, a presence boost which was appropriate during one section of a performance may become harsh during another section.

The two most common solutions are automation and multi-band dynamics processing. Automation is only convenient when the spectral changes occur over a long period of time, and aren't repetitive. Typical multi-band dynamics processors work to some extent, but with inconvenient downsides.

Multi-band dynamics vs. dynamic EQ

Multi-band compressors/expanders and dynamic EQs work in a similar way. They both split the input signal into multiple parallel paths. Each path is filtered to restrict its frequency range, then sent into a compressor or expander.

A dynamic EQ applies the gain reduction/expansion to the gain parameter of a parametric equaliser which processes the original input signal.

Multi-band compressor/expanders apply their gain reduction directly to each filtered signal, then combine them to reconstruct the original wide-band input signal.

This reconstruction approach has some downsides:

Static phase shift

When the band-limited signals are combined to reconstruct the input signal, a static phase shift is present at their cross-over point. The band-limiting can be achieved using linear-phase filters, however these incur high latency and can degrade transient response at lower frequencies.

Spectral shape

Multi-band processors typically afford less precise frequency adjustment than a parametric equaliser. If steeper filters are used to provide greater precision, phase shift at the crossover points increases.

Bands cannot overlap

Some multi-band processors get around the phase response issue, but are still left with a problem -- the bands cannot be overlapped! This can pose significant problems when a combination of gentle character modification and precise correction is required.

But Multi-band processors do have an advantage over most dynamic EQs. As a boost or cut increases, the width reduces. This is similar to the proportional Q response or gain / Q dependency of many well loved analogue EQ processors.

When using an EQ which does not have this gain / Q dependent response, gain changes often require Q changes to maintain the desired effect. Of course, this is highly undesirable if the gain is being modulated dynamically! See Gain-Q Dependency for details.

The Oxford Dynamic EQ combines the benefits of dynamic EQ with the Oxford EQ's Type 3 gain / Q dependency, giving you the best of both!

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