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filters as precise and clean as possible. For controlled
generation of distortions we recommend using enhancers or
any other specialised processors with proper built-in anti-
aliasing technology.
4.4 Non- Linear Phase EQ
Phase shift in equipment is probably one of the most
misunderstood topics in audio. Phase shifts often get blamed
for anything that is not classed as typical distortion. The reality
is that all analogue EQs produce a deviation from linear phase
which is specifically related to the shape of the EQ curve, and
it is precisely these phase changes which produce the required
gain reductions. This is a very natural process which can be
found in the audio characteristics of rooms, materials and
elsewhere.
Though it is not possible for us to detect phase in isolation,
the phase shift of an EQ can often be the cause of the ‘magical’
sound of that device once the EQ’d signal is added back into
the mix. For example, the Duende channel EQ derived from
the SSL analogue consoles – plenty of phase shift and plenty
of magic!
In contrast, a linear-phase EQ delays all frequencies by the
same amount. This can only be achieved in the digital domain
by using special techniques. While this process is very
effective in certain situations (eg. ‘surgically’ removing
troublesome frequencies), it should not be considered as a
superior tool for the majority of EQ tasks.
Linear phase equalisers have become popular over the past
few years due to the proliferation of powerful digital
processors. We decided not to go down that route with X-EQ
and we think you’ll agree with that decision. Maybe linear
phase EQ is something we will explore in the future but…
who knows? An equaliser not only changes the relative
frequency balance of a signal but also its phase. If you EQ a
sound until it sounds right or natural, then the chances are that
you are EQing to make it sound in phase with the rest of the
mix. We need say no more on this subject.
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