This Article Originally Published April 1998

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:

My website address is:

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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