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EQ (part 2)

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If Figure 1 shows a flat response between about 20Hz and 20kHz, Figure 2 and
Figure 3 show two of the curves you might expect to get from a mixing console
EQ. Oddly enough, measuring the EQ and plotting the curve is something that
only 0.001% of recording and sound engineers ever get round to doing at any
stage in their creative careers, and only 0.0001% have their own equipment to
do it to any reasonable accuracy. Even if it’s hardly ever done except
on the test bench, it’s a useful concept which you can carry around in
your head without ever bringing to the forefront of your mind. So if a producer
ever says to you, “Let’s have a little more presence in the vocal”,
your subconscious mind will retrieve the bell shaped curve of Figure 2 from
your memory bank while your conscious mind adjusts the controls and judges the
sound. In Figure 2 we are adding an EQ boost, and there are three parameters
that we would like to be able to control (if the EQ has knobs for all three).
First and foremost is the frequency: this boost could be centred on any frequency
according to the instrument and according to which characteristics you want
to accentuate. Second is the gain, which is the degree of boost and can be measured
in decibels at the centre frequency. Some mixing consoles even calibrate this
control in dB, and a good thing too! You might like to have a range of up to
12 or 15dB as a maximum. Gain can also be negative to produce an EQ cut, which
would be written as a gain of -6dB, or whatever, at the centre frequency, so
the curve would dip downwards. EQ cut, by the way, is a vastly underutilised
resource on many consoles, but more on this later. The third parameter which
is only occasionally offered on a console EQ is Q. Q, as well as being the star
of the last ever episode of Star Trek The Next Generation, or so my crystal
ball informs me, is a measure of the width of the bell shaped curve – the bandwidth
as some might say. A low Q – 0.3 is low – will allow the EQ to cover a wide
range of frequencies while a higher Q – 5 is high – will allow you to home in
on a particular feature of the sound.


The bell shaped curve of Figure 2 is often referred to as ‘peaking’
EQ, and applies to all mid frequency range EQ sections and a good proportion
of high and low frequency EQ sections too. Figure 3 shows a ‘shelving’
EQ where the boost – or cut – extends from the set EQ frequency all the way
to the extreme end of the range. I have shown a low frequency shelving EQ in
boost mode, but it could have been a high frequency cut with a similarly shaped
but differently orientated curve. It isn’t possible to say which type of
curve is better, it depends on what you want to achieve and some consoles have
a button to allow you to choose.

David Mellor

Mix Digital, Sound Analog!

Mix Digital, Sound Analog!

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David Mellor