Rane MM 12 Operations Instructions download pdf (Page 10)

Manual-10

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103297

MOJO GLOSSARY

balanced line The recommended method of interconnecting audio

equipment. A balanced line requires three conductors: a twisted-pair

for the signal (positive and negative) and an overall shield. The

shield must be tied to the chassis at both ends for hum-free intercon-

nect.

bandwidth Abbr. BW The numerical difference between the upper

and lower -3 dB points of an audio band.

clipping What occurs when a unit tries to produce a signal larger

than its power supply. The signal takes on a flat-topped, or clipped

shape. When an amplifier tries to go above its max power, it clips.

compressor A signal processing device used to reduce the

dynamic range of the signal passing through it. For instance, an

input dynamic range of 110 dB might pass through a compressor and

exit with a new dynamic range of 70 dB. The modern usage for

compressors is to turn down (or reduce the dynamic range of) just

the loudest signals. Other applications use compressors to control the

creation of sound. When used in conjunction with microphones and

musical instrument pick-ups, compressors help determine the final

timbre by selectively compressing specific frequencies and wave-

forms.

connectors Audio equipment uses different styles:

RCA An unbalanced pin connector commonly used on

consumer and some pro equipment; aka phono plug

XLR A 3-pin connector common on pro audio equipment.

Preferred for balanced line interconnect; aka Cannon plug

¼" TRS 1. Stereo ¼" connector consisting of tip (T), ring (R),

and sleeve (S) sections, with T = left, R = right, and S =

ground/shield. 2. Balanced interconnect with the pos & neg

signal lines tied to T and R respectively and S acting only as an

overall shield. 3. Insert loop interconnect with T = send, R =

return, and S = ground/shield. [Think: ring, right, return]

¼" TS Mono ¼" connector consisting of tip (T) [signal] and

sleeve (S) [ground & shield] for unbalanced wiring.

constant-Q equalizer (also constant-bandwidth) The

bandwidth remains constant for all boost/cut levels. Since Q and

bandwidth are interrelated, the terms are fully interchangeable.

decibel Abbr. dB (named after Alexander Graham Bell). The

preferred method and term for representing the ratio of different

audio levels. Being a ratio, decibels have no units. Everything is

relative. So it must be relative to some 0 dB reference point. A suffix

letter is added to distinguish between reference points:

0 dBu A reference point equal to 0.775 V

+4 dBu Standard pro reference level equal to 1.23 V

0 dBV A reference point equal to 1.0 V

-10 dBV Standard reference level for consumer and some pro

audio use, equal to 0.316 V. RCA (phono) connectors are a

good indicator of units operating at -10 dBV

dynamic range The ratio of the loudest signal to the quietest signal

in a unit or system as expressed in decibels (dB).

expander A signal processing device used to increase the dynamic

range of the signal passing through it. Expanders complement

compressors. For example, a compressed input dynamic range of 70

dB might pass through a expander and exit with a new expanded

dynamic range of 110 dB. Modern expanders usually operate only

below a set threshold point, i.e., they operate only on low-level

audio. The term downward expander describes this type of applica-

tion.

ground Any electrical reference point for measuring voltage levels.

Usually a large conducting body, such as the earth or an electric

circuit connected to the earth. Chassis should always be at earth

potential. WARNING: SHOCK HAZARD

Never use an AC line cord ground-lift adapter or cut off the 3rd

pin. It is illegal and dangerous.

headroom The level in dB between the typical operating level and

clipping. For example, a nominal +4 dBu system that clips at +20

dBu has 16 dB of headroom.

hum Unwanted sound contaminating audio paths due to EMI

(electro-magnetic interference) caused by AC power-lines &

transformers getting into unbalanced, poorly shielded, or improperly

grounded connecting cables. Hum has a definite smooth (sine wave)

repetitive sound based on the harmonics of 50/60 Hz such as 100/

120 Hz and 150/180 Hz.

interpolating Term meaning to insert between two points. If a

graphic equalizer’s adjacent bands, when moved together, produce

a smooth response without a dip in the center, they are interpolat-

ing between the fixed center frequencies.

levels Terms used to describe relative audio signal levels:

mic-level Nominal signal coming directly from a microphone.

Very low, in the microvolts, and requires a preamp with at least 60

dB gain before using with any line-level equipment.

line-level Standard +4 dBu or -10 dBV audio levels.

instrument-level Nominal signal from musical instruments

using electrical pick-ups. Varies widely, from very low mic-levels

to quite large line-levels.

limiter A compressor with a fixed ratio of 10:1 or greater. The

dynamic action prevents the audio signal from becoming larger than

the threshold setting.

Linkwitz-Riley crossover The most preferred active crossover

design. It features steep 24 dB/octave slopes, in-phase outputs, and

flat amplitude response. Due to the in-phase outputs the acoustic

lobe resulting when both loudspeakers reproduce the crossover

frequency is always on-axis (not tilted up or down) and has no

peaking.

noise 1. Interconnect. Unwanted sounds contaminating audio paths.

RFI (radio frequency interference) caused by broadcast signals

leaking into unbalanced, poorly shielded, or improperly grounded

connecting cables. Also by light dimmers, motor controls and

computers. 2. Music. A random mix of audio frequencies not

harmonically related, sounding like radio static.

polarity A signal’s electromechanical potential with respect to a

reference. For example, a microphone has positive polarity if a

positive pressure on its diaphragm results in a positive output

voltage. polarity vs. phase shift: polarity refers to a signal’s

reference NOT to its phase shift. Being 180 degrees out-of-phase and

having inverse polarity are DIFFERENT things. We wrongly say

something is out-of-phase when we mean it is inverted. One occurs

over a period of time; the other occurs instantaneously.

Q (upper-case) Quality factor. Defined to be the ratio of the center

frequency f divided by the bandwidth BW for a bandpass filter.

signal-to-noise ratio The ratio in dB between a reference level

and the noise floor. For example, a signal-to-noise ratio of 90 dB re

+4 dBu, means the noise floor is 90 dB below a +4 dBu ref.

unbalanced line An audio interconnect scheme using one wire

with an overall shield. The shield must perform two functions: act as

the return signal path (ground) and to protect the conductor from

noise (shield). Consequently this method is vulnerable to hum &

noise problems.

unity gain A gain setting of one. The level out equals the level in.

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Rane MM 12 Operations Instructions Page 10

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