[ddots-l] Re: Graphic versus Other EQ Types
- From: "Farfar Carlson" <dgcarlson@xxxxxxxxxxxxx>
- To: <ddots-l@xxxxxxxxxxxxx>
- Date: Tue, 21 Dec 2010 11:03:34 -0800
Chris,
Very nice! Thanks for the tutorial.
Dave
Composed on a Dell Latitude 630 in the general vicinity of my Audio
Recording and Mixing Studios, San Francisco Bay Area.
----- Original Message -----
From: "Chris Smart" <chris_s@xxxxxxxxxxxx>
To: <ddots-l@xxxxxxxxxxxxx>
Sent: Tuesday, December 21, 2010 10:37
Subject: [ddots-l] Graphic versus Other EQ Types
Here are some more thoughts on EQ types, starting with those that
affect a more broad frequency range.
High and Low Pass filters (hpf, lpf) allow frequencies above or
below a cut-off frequency to pass through, hence their name. For
example, a high pass filter set to 200HZ, will let everything above
that frequency through, and will drastically attenuate things below
that frequency. Note that in most designs, the cut-off frequency is
where things are attenuated by 3dB, so don't think of the effected
area as starting exactly at that point.
HPF and LPF are very useful for, say, getting rid of some lows on
guitars or keyboards, so they don't interfere with the upper bass
notes or the bottom part of the vocals.
Shelving EQ affects a wide range of frequencies, but a lot less
drastically than hpf/lpf. If you want to roll off highs or lows,
but not get rid of them entirely, this is the tool to
use. Adjusting the Q parameter on a shelving EQ specifies the
relative steepness of the slope.
An example might be a low frequency shelf that attenuates by around
6dB per octave.
Parametric EQ (called peak/dip in the Sonitus plug-in), is a tool
for very precise adjustments. Let's compare parametric and graphic
EQ types.
On a thirty-one band graphic equaliser, each band covers one third
of an octave. You can work this out from the fact that one octave
represents a doubling
- or halving - of frequency, and there are ten octaves between 20Hz
and 20kHz.
What if you want to get more precise than that?
What if, for example, you want to boost slightly around 450HZ but
you only have bands at 400 and 500 HZ? What if you have a spike in
the vocals at 3.7K but only have bands whose center frequencies are
3.1 and 4K? What if the attack of your kick drum is around 3.6K and
you want to boost just that by a couple dB?
Think of each band on a graphical EQ as having a fixed Q parameter
or slope you cannot change. A frequency slider on a graphic EQ
affects a fixed range of frequencies above and below it.
Q represents the shape of the EQ response curve. It's the ratio of
the center frequency to the difference of the upper and lower
frequencies that are being affected.
The upper & lower frequency's are defined as the point where they
are 3 dB different in level than the center frequency.
using a single band of a parametric EQ, Here's an example. If we
are boosting 6 kHz by 12 dB , and the EQ filter curve shows we are
boosting at 9 dB at 4 kHz & 8 kHz respectively, we can calculate
the Q parameter by doing the following:
center frequency divided by upper frequency minus lower frequency.
In this case, 6,000 divided by the result of 8,000 minus 4,000
equals 1.5.
Q = 1.5
So, the Q value that represents this particular equalization curve
is 1.5. This is quite a wide range of frequencies.
A more extreme example would be a Q of 0.4, which would span 3 octaves!
If your EQ plug-in describes this as bandwidth, the important thing
to remember is that Q and bandwidth are of inverse proportion. That
is, the higher the bandwidth number, the lower the Q number. The
higher the Q number, the lower the corresponding bandwidth
number. You can find formulas online to convert bandwidth to Q or
Q to bandwidth, if you absolutely need to know.
The good thing is that you don't have to do math like this to get
the results you want, only listen and practice, practice, practice!
1. Solo the track or tracks you are trying to affect. Loop a
problem area if necessary.
2. Turn the gain up or down drastically, at least 10dB.
3. Keep the Q number fairly low to start.
4. Sweep the frequency value around until you get close to your
target area.
5. Narrow the affected frequency band by raising the Q value, and
zero in on the target as precisely as you can.
6. Back the gain adjustment off to get the desired amount of boost
or attenuation.
7. Listen to the affected track or tracks in the mix, to see if
what you just adjusted improved things or made them worse.
If you are used to thinking in terms of musical pitches and
octaves, as found on a keyboard or other instrument, learn the
frequencies of some notes by their HZ value.
Fourth octave A is 440HZ. Double that and you get 5th octave A, 880
HZ. Cut it in half and you get 3rd octave A, 220 HZ. If you
continue halving, you end up at the lowest A on a piano, way down
at 27.5 HZ.
1KHZ is just above 5th octave B natural. Learn to recognize
doublings or halvings of that frequency, just because the numbers
are easier to work with - 1K 2K 4K etc.
Here's a handy chart that shows the frequencies of our notes, and
their wavelengths.
http://www.phy.mtu.edu/~suits/notefreqs.html
General Tips:
1. Keep in mind that a soloed track that sounds full on its own,
probably takes up too much sonic space inside a mix. Things that
sound small on their own can sound perfect in a mix. That massive
guitar sound you love soloed, might totally obscure the vocals in a
crowded mix.
2. You'd be surprised how our brains can fill in missing
frequencies. We can even imagine the fundamental of a note if the
harmonics are all there, but the fundamental is missing!
3. Carving out frequency space for each instrument is one of the
most important aspects of mixing. If panning things to different
stereo positions doesn't clarify things, consider narrowing the
frequency ranges of some instruments, or mirroring some EQ changes.
For example, if one instrument has a lot of midrange, reducing the
midrange on other instruments might carve out some space for
it. You might want to attenuate some frequencies of the hi-hats
where the crispiness of the snare drum is, or roll off some low
thud of the kick drum, so it interferes less with the bass.
Last but not least, this sort of information is out there for the
taking... books on mixing or recording, manuals for the particular
plug-ins you're using, articles in magazines like Mix or Sound on
Sound, discussions in the Cakewalk forums or those at
www.gearsluts.com etc. etc. etc. Wikipedia and Google are your
friends too!
Chris
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