High and low impedance? Mike level? Line level? What are those audio tech-types talking about? And why
all the funny-looking plugs and adapters?

If these things confuse you, you’re not alone. Many videomakers cringe at the thought of all that audio
cable spaghetti, not to mention the different connectors needed for each type of cable.

Nonetheless, it’s important to know about connectors and their uses. This will allow you to make proper
connections for the best possible performance from your audio gear.

So don’t worry if all this impedance, level, or connector stuff confuses you. Just hang in there through the
end of this article and we’ll have you hooking up your audio gear like a pro.

Mike Level Signals
To learn more about connectors, we’ll need to take a look at the different types of signals we’ll be dealing
with. I’ll suggest the various kinds of connectors that work with these signals as we go along. First, let’s look
at the signal that a mike produces–the "mike level" signal.

The origin of this signal is a clever device known as an audio transducer.
Audio transducers convert physical movement (sound) into electricity. The varying strength of this voltage is
a signal. A microphone, which is a transducer, generates a variable voltage signal that contains the audio
information the mike picks up. This signal transfers over a cable to your amp, mixer, tape deck, VCR or what
have you.

Because mike level signals are weak, the mike input of audio and video gear always connects the signal to
a preamplifier. The preamp boosts the mike signal up to a level that the audio circuitry can use.

The mike signal travels down the cable toward the amplifier in one of two ways: balanced or unbalanced.
Unbalanced signals travel on cable using a single conductor wire. A fine wire or foil shield in the outside
layers surrounds the single conductor. This shield has two jobs in an unbalanced cable:
it shields the inner conductor from external interference, and it acts as a ground reference to complete the
microphone circuit.

The shielding function of the unbalanced signal is very important, because external interference can bring
extra noise into your audio. This can include A/C hum from nearby wires, machinery, electric motors, or
magnetic fields. Interference is a big problem with mike level signals because, as we said before,
mike level signals are very weak, sometimes on the order of millionths of a volt. Since the shield connects to
ground, any outside noise that gets to the shield drains harmlessly away.


Balanced cable is physically like unbalanced cable, but with an extra center
conductor. The microphone signal runs down these conductors without using the shield in the
circuit. The two conductors run into the primary side of an isolating transformer in the input. While this
transformer does not effect the audio signal, any external noise that gets past the shield will travel down the
conductors and through the transformer in opposite directions (out of phase). This effectively cancels out any
external noise which gets past the shield. Balanced connectors and cables are far better at minimizing outside
noise in your audio signal.

Connectors used with unbalanced mike cables include the very common 1/4-inch phone plug. More
popular on camcorders, however, is the 1/8-inch mini phone plug. Manufacturers insulate the tip of
these plugs from the rest of the plug body. The tip then carries the positive, or "hot" signal, while the slender
shaft portion of the plug connects to the grounded shield.

The 1/8-inch mini phone plug has been a matter of debate for years. It does not often fit tightly into its
jack, and is easy to pull loose. Part of the problem is the tiny (and therefore weak) parts that make up the
jack. They are just too easy to break. For this reason, many semi-pros have their gear converted from 1/8- to
1/4-inch.

Phone plugs also find use in audio patchbays, musical instrument connections and were originally used in
telephone systems (which is where their name comes from). Part of the reason both 1/4- and 1/8-inch phone
plugs are so popular is the simplicity of their design: you simply shove the plug into the jack, and you’re
ready to go.

Unbalanced lines are commonly used with high impedance microphones. The impedance of an item, such
as a microphone, states its internal resistance to a signal. This resistance comes from different components
within the device.

A high impedance mike on an unbalanced cable offers maximum signal output on average cable lengths.
This setup is so common that cheaper high impedance mikes come with unbalanced cables and phone plugs
permanently installed. The problem with unbalanced lines is that they’re more susceptible to outside noise
(especially on long runs).

So along comes the XLR (or "Cannon") connector, commonly used with balanced cables. This is a three-
pin, metal case, locking connector that fastens securely to the cable, assuring a solid connection all the way
around.

One of the best features of the XLR connector is its lock. This stops the connector from accidentally being
yanked out if someone trips over the cable (a common problem with phone plugs; just ask any electric guitar
player). This lock is such an advantage that many audio pros wire the XLR connector for use with their non-
balanced gear.

Also, don’t assume you have an unbalanced cable just because it has a phone plug attached to it. The 1/4-
inch stereo phone plug also shows up on balanced cable to make all kinds of audio connections in
professional gear.


Line Level
Much of the audio gear made for use with video works with line level inputs and outputs. Audio mixers,
VCRs, and ATRs (audio tape recorders) all put out and accept a line level signal.

A line level signal is the signal from a pre-amp stage, and is usually at the level of 0.7 to 2 volts.
That’s quite a bit higher than a mike’s output. Because a line level signal is considerably stronger then a mike
signal, noise becomes somewhat less of a problem. Hence line level cables most often use unbalanced
connectors. Still, some long line level runs found in TV studios and production houses use balanced lines for
cleaner results.

The most common line level connector is the RCA plug. If you’ve ever hooked up a stereo system, or your
camcorder to your VCR, you’ve used RCA plugs. This small plug has a wrap-around metal crown on the
outside edge with a large, single pin in the center. A female RCA jack is the receptacle on most equipment.
RCA connectors are also common on consumer stereo equipment–receivers, tape decks and the like.

As mentioned before, some audio patch bays use the 1/4-inch phone plug as an unbalanced connector. But
some patch bays also use short RCA cables. The problem with such setups is the tendency for the male end
of the RCA connector to get bent and worn out, which makes for a weaker connection.

Also found on consumer equipment is the DIN connector. DIN stands for Deutsche Industrie
Norm
(meaning German Industry Standard). These are smaller, plastic covered push-in connectors. The
five pin is the most common, although they range from three to as many as twelve pins for pro use. DIN
plugs became popular on European exports of consumer audio gear in the sixties and early seventies, but you
seldom see them today in audio for video gear.

Professional equipment often makes use of XLR connectors for line level signals primarily for the locking
mechanism, and because XLR connectors are downright tough.


Cabling
While we’re on the subject of connectors, we may as well take a look at the different kinds of
cabling.

You can wire any balanced cable to work as an unbalanced cable as well. Because it’s carrying two signals,
balanced line uses a cable with two center conductors and a shield. As stated earlier, the advantage of
balanced cabling is that it doesn’t pick up as much outside noise. Also, balanced cable on a low impedance
mikes can successfully run to lengths of 1000 feet or more without significant quality loss.

Standard unbalanced cable generally finds use with high impedance equipment and uses only a single
center conductor with the surrounding shield. A high impedance mike will produce a greater output for a
given sound than a low impedance mike given the same conditions. However, long runs with high
impedance equipment are out. Twenty five feet seems to be a maximum length for this type of cable. Beyond
that, the higher frequencies in the signal begin to be reduced.

It’s important to use high quality cable for either type of line. Cables like Beldon’s 8451 or
Comprehensive’s CMC-2 are excellent examples of dual center conductor audio cable. You can wire this
cable either balanced or unbalanced and it has good flexibility.

Poor quality cable will sometimes use non-braided shielding that swirls around the center conductor. The
insulation of such cable may be a plastic and rubber combination. This will feel stiff to the touch. Such cable
will not shield very well and external noise and hum will affect the signal. Further, the metal center
conductor is usually cheap and the cable will probably fail in short order.

Speaker Level
Speaker playback is a daily necessity in any audio production house, and speakers must connect to
power amplifiers to operate. The high level of a speaker signal eliminates the need for any concern about
external noise protection. As a result, most speaker cable is simple unshielded two-conductor cable, not
unlike A/C power cable.

Many manufacturers make high-quality speaker cable. Manufacturers mark speaker cable along one side
with a color stripe. This helps you maintain polarity so that, when hooked up, your speakers are both moving
in the same direction at the same time.

Your speakers may also have connectors colored red (or marked positive) and black (or marked negative)
for proper connections. The amplifier end uses several different kinds of connectors. Screw-down connectors
and color-coded push clamps are common on consumer amplifiers. On the professional side are banana plugs
(especially on public address equipment).

Banana plugs are large, single-pin, color-coded connectors. They are fast and easy to use, and offer a fairly
solid connection. Different variations of the banana plug find use industry wide in hooking up testing gear
for electronic repairs.

Other types of speaker connectors include phone plugs, which connect public address systems and musical
instrument amplifiers to their speakers, and split spade connectors, which use flattened pins spread out into
an L or other shape.

Adapters
We can’t conclude a discussion of audio connectors without discussing adapters. Sooner or later you’re going
to need to connect a mike cable to a recorder or amp and discover a mismatch. Your phone plug just won’t
go into the XLR jack. You just traveled 40 miles to get this shot and the audio is important. What to do?

The professional would reach for their trusty box of adapters and fix the situation in seconds. An
assortment of adapters is just as important as extra batteries and cables. Without that box of adapters, you’ll
probably have to scrap the shoot until a later date.

The larger the variety of adapters you carry, the better insurance you have against problems. Connectors
can turn a mini phone plug into an XLR or vice versa. Adapters will allow you to use audio cables for video
in an emergency and also vice versa. In fact, adapters are available to convert almost any kind of connector
to almost any other. Start collecting yours today; you never know when you’ll need them.

Sometimes the input impedance of the recorder or mixer does not match your gear. Or perhaps you wish to
use a low impedance mike with a high impedance input. What can you do? The line matching transformer is
the answer. This transformer has a primary side (input) that accepts the balanced line. The secondary side
(output) sends out an unbalanced line. This transformer mounts onto the cable at the connector of your amp.
The advantage, of course, is to match the impedance between your mike/cable combination and your audio
input. When impedances are matched between equipment, any signal passed between them is at its best.

Well, now you know something about the different types of connectors and what they do. You can use
what you’ve learned to prepare any cables you’ll need for a shoot or to do proper hookups in your studio.
You should also have a better understanding of how cable and microphone combinations work together and
how connectors differ as well. Further, the value of keeping a collection of adapters in case of emergencies
should be clear.

Okay. Keep those connections tight until next time.

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