Specifications

22
MIC AND LINE — WHAT DO THEY MEAN?
Some mixers have switches on the rear panel for setting each input or
output jack for mic level or line level. These refer to the signal level or
intensity that the input is designed to accept.
A mic-level
or microphone-level signal is the amount of voltage that
comes out of a microphone when someone speaks into it - just a few ten-
thousandths of a volt. (Of course, this voltage varies somewhat in response
to changes in speaking volume and source-to-mic distance.) A line-level
signal is approximately one volt, or about 10,000 times as strong as a mic-
level signal, so the two do not ordinarily use the same input. Connecting a
microphone to a line-level input will result in almost no sound at all, because
the signal is so faint that the line input cannot hear it. Connecting a line-level
source (such as a CD player) to a mic-level input will cause the sound to be
loud and distorted because the line signal is much stronger than what the
mic input will accept. Inputs and outputs on better mixers are switchable for
either mic or line level operation.
You may also encounter jacks marked “aux
” (or “tape”) and “phono”.
Aux-level inputs and outputs are found on many kinds of equipment,
including VCR’s, tape recorders, CD players, and some computer sound
cards. Aux-level is somewhat close to line-level, but aux-level inputs and
outputs are nearly always unbalanced, using RCA or 1/4” connectors.
Microphones cannot be connected directly to aux inputs. Jacks marked
phono are for phonograph turntables only, and are not compatible with
anything else.
MIXER FEATURES
On the front panel of the mixer (shown on page 21) are low-cut filter switches
for each input. Such switches are often labeled “In” and “Out” rather than “On”
and “Off”, a custom resulting from the fact that some additional circuitry is being
placed “in” the signal path. Moving these switches to the “In” or “On” position
filters out some of the low frequencies from the signals on those channels. This
feature comes in handy for reducing the rumbling noises which often come from
air conditioning, wind noise, etc. The limiter
feature is extremely useful, and it will
not hurt to leave it on all the time. A limiter acts as a ceiling for the audio signal,
and tries to keep it below the point at which distortion occurs. Some limiters can
be adjusted to activate at different levels, called the threshold. The switch marked
“osc” controls the built-in tone oscillator
, sometimes called a tone generator. This
tone, usually at a frequency of 1,000 Hertz, is used for adjusting several
connected pieces of equipment (see section on setting levels for more details.)
On the rear panel of the mixer, (shown on page 21) on the right side, is a jack
marked “mix bus”. This jack allows you to connect two mixers together when
your application requires more than the inputs available on one mixer. All input
signals from both mixers would then be combined at each mixer’s output. In
other words, the outputs of each mixer would be duplicates of each other.