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by Andy
Cahan
Hi , this is Andy Cahan, The Demo Doctor, making another house
call. During the past month, I've received a lot of questions
asking me about Equalization. So I thought I'd focus part
of this column on answering that question.
Equalization
is the term used to describe the process of changing the balance
between high and low frequencies. Equalizers allow us to selectively
boost and/or cut specific frequencies or bands of frequencies.
With regard to equalization of the instruments you are recording,
you must first assign the range of each instrument into its
own frequency so that it won't interfere with any of the other
instrument frequency ranges.
There
are many types of equalizers and they get used in many different
ways by different people. In general, "Parametric Equalizers"
allow for very specific effect with adjustable Q and frequency
control for each frequency band.
"Graphic
Equalizers" feature as many as 31 individual sliders centered
on fixed frequencies and tube equalizers utilize vacuum tubes
in their circuits as opposed to transistors ("solid state")
and are often preferred for their warm sound.
All
mixers provide some kind of EQ, switchable on or off, in the
signal path. These days, semi-pro consoles usually feature
a couple of overlapping bands of semi-parametric EQ on the
low-mids(200-2K) and hi-mids(1.5K-7K), and one EQ each for
the low(100 hz) and high(10K) bands with shelving switches
and low-frequency roll-off. Professional consoles offer fully-
parametric designs and more overall flexibility, as you might
expect. Since we can't all afford Neve VR consoles at home,
another option for small studios is outboard equalizers. Get
a couple of good ones and insert them into the signal path
and print through them to tape. This will definitely take
your sounds up a notch without totally blowing your college
fund.
I've
also received questions inquiring about dynamics. The term,
"dynamics" refers to whether a sound is "soft" or "loud".
The ability of a recording medium to reproduce the difference
between soft and loud is called its "Dynamic Range". Vinyl
records and cassette tapes have a limited dynamic range of
about 20 db, while modern CD's and Digital Audio Tape (DAT)
are capable of full dynamic range- that's 100 db! The limiting
factor of how much of that range you get to actually hear
is determined by the speakers, amplifiers and the room you're
listening in.
We've
all heard terms like "bright", "dull", "deep" and "thin" used
to describe music. Two major factors complicate this affair.
The first is that we all hear the same thing differently;
one person's "bright" is another person's "dull". The second
is the accuracy or lack thereof, of our sound source, i.e.
the speakers and amplifiers. Technically, the audible frequency
range for human hearing is 20 Hertz(Hz) on the low end and
20 Kilohertz(Khz) on the high end. Most people's hearing range
falls between 40Hz and 16 Khz and in fact, the specified frequency
range of FM radio is 50Hz to 15Khz. A typical car radio, boom
box or home stereo has two EQ knobs on it. The "Low" and "High"
knobs are usually centered at 100 Hz and 10 Khz respectively
with a broad "fixed Q".
"Q"
refers to the range of frequencies affected by the boost or
cut and is expressed in octaves. Their effect is not subtle
but for consumer applications this is simple, convenient and
usually sufficient. The loudness button is simply a low frequency
boost that compensates for the apparent lack of low frequencies
at low listening levels. While the human voice is the most
dynamic, all of these instruments present a similar problem
to the engineer. How can we preserve the performance, that
is the soft and loud of it, and get it accurately on tape?
With these instruments, we usually have to use a microphone.
The
two main types of microphones are "dynamic", which have no
active electronics involved in amplifying the input signal,
and "condenser", which require either batteries or "phantom
power" to power their electronics. Both types have a thin
membrane, called the diaphragm, that vibrates and that physical
vibration is translated into an electronic signal.
In
general, condenser mikes are brighter and have a broader frequency
response, but they are more fragile. That's why you usually
see an SM57, a general purpose dynamic mike, in the lead singer's
hands at a concert. They can withstand a lot of abuse. Classic
condenser microphones like the Neumann U-47 and AKG C-12 use
vacuum tube electronics and are treasured for their unique
sound. They are rather large and have diaphragms 2 inches
in diameter.
Ribbon
microphones are another vintage design that incorporate a
thin rectangular strip as its diaphragm, hence the name.
PZM
designs are a relatively new invention. They work on a completely
different principle and don't look anything like traditional
microphones. The signal created by the microphone is very
small and it is the microphone pre-amp that increases this
level to what is known as "line-level" for interfacing with
the mixing board. This is yet another link in the chain with
its opportunity to affect the sound, and they do.
Everyone
has his favorite microphones and pre-amps for different situations
and most do color the sound. The important thing is whether
you like that color and if it's appropriate for the particular
situation at hand. Here again, we run into the concept of
"flat frequency response" and again it is relatively meaningless.
Most microphones are not "flat" and some are better suited
for certain jobs than others. As always, you need a reference,
and in this regard, frequency response charts and the like
can be useful.
That
about does it for this month. If you have any questions about
demo making or recording in general, send them to the Demo
Doctor. If you are on the internet, you can e-mail me at:
andycahan@verizon.net.
My website address is:
http://allentertainment.net.
Or, snail mail me at:
Andy
Cahan
PO
Box 261969
Encino,
CA 91426-1969
Phone:
818/489-4490
Fax:
818/728-9059
Andy
Cahan is a 35-year veteran of the music industry.
As a recording engineer and record producer, Cahan has worked
with such artists as Ringo Starr, Harry Nilsson, Flo & Eddie
and Eric Carman.
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