[ddots-l] Re: Graphic versus Other EQ Types
- From: "Sean A. Cummins" <seanacummins@xxxxxxxxx>
- To: <ddots-l@xxxxxxxxxxxxx>
- Date: Tue, 21 Dec 2010 11:50:50 -0700
Chris,
Are you the Chris that is looking for mastering work? If so, write me off
list.
Sincerely,
Sean A. Cummins
Consultant
InVision Technical
PO Box 2015
Cottonwood, AZ 86326
(928) 646-7233
SeanACummins@xxxxxxxxx
Leading the edge of technology for over 27 years.
----- Original Message -----
From: "Chris Smart" <chris_s@xxxxxxxxxxxx>
To: <ddots-l@xxxxxxxxxxxxx>
Sent: Tuesday, December 21, 2010 11:37 AM
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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