Behringer MDX1400 - Manual (Page 22)

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AUTOCOM PRO MDX1400
5.4 “Voice-Over” Compression (“Ducking”)
The BEHRINGER AUTOCOM PRO can be used to automatically reduce music to a background level, when an
announcer is speaking through a microphone. For this purpose, the BEHRINGER AUTOCOM PRO is used as
an automatic fader and is controlled by the announcer’s microphone, which is connected to the SC RETURN
input via a preamplifier. The music output and the announcer’s voice, are then mixed. This application is known
as “voice-over” compression or “ducking” and is commonly used in discos, radio stations etc.
5.5 Triggering Additional Sounds From A Rhythm Track
This technique is used to give a rhythm track more “punch”. For this purpose, only the Expander/Gate section
is required and the Compressor and Dynamic Enhancer sections are switched off. The bass guitar track is
connected to the audio chain of the BEHRINGER AUTOCOM PRO, while the bass drum is connected to the
SC RETURN input. By activating the SC EXT switch, the bass guitar is now triggered by the bass drum.
Another application allows the sound of the bass drum to be supported or extended by other instruments
(synthesizers etc.), where the bass drum is used to trigger a new sound, which is then mixed into the track.
6. TECHNICAL BACKGROUND
By employing current modern analog technology it is possible to manufacture audio equipment with a dynamic
range of up to 125 dB. In contrast to analog techniques, the dynamic range of digital equipment is
approximately 25 dB less. With conventional record and tape recorder technology, as well as broadcasting,
this value is further reduced. Generally, dynamic restrictions are due to noisy storage and transmission media
and also the maximum headroom of these systems.
6.1 Noise As A Physical Phenomenon
All electrical components produce a certain level of inherent noise. Current flowing through a conductor leads
to uncontrolled random electron movements. For statistical reasons, this produces frequencies within the
whole audio spectrum. If these currents are highly amplified, the result will be perceived as noise. Since all
frequencies are equally affected, we term this white noise. It is fairly obvious that electronics cannot function
without components. Even if special low-noise components are used, a certain degree of basic noise cannot
be avoided.
This effect is similar when replaying a tape. The non-directional magnetic particles passing the replay head can
also cause uncontrolled currents and voltages. The resulting sound of the various frequencies is heard as
noise. Even the best possible tape biasing can “only” provide signal-to-noise ratios of about 70 dB, which is not
acceptable today since the demands of listeners have increased. Due to the laws of physics, improving the
design of the magnetic carrier is impossible using conventional means.
6.2 What Are Audio Dynamics?
A remarkable feature of the human ear is that it can detect the most wide ranging amplitude changes – from the
slightest whisper to the deafening roar of a jet-plane. If one tried to record or reproduce this wide spectrum of
sound with the help of amplifiers, cassette recorders, records or even digital recorders (CD, DAT etc.), one
would immediately be restricted by the physical limitations of electronic and acoustic sound reproduction
technology (see fig. 6.1).
The usable dynamic range of electro-acoustic equipment is limited as much at the low end as at the high end.
The thermal noise of the electrons in the components results in an audible basic noise floor and thus
represents the bottom limit of the transmission range. The upper limit is determined by the levels of the internal
operating voltages; if they are exceeded, audible signal distortion is the result. Although in theory, the usable
dynamic range sits between these two limits, it is considerably smaller in practice, since a certain reserve
must be maintained to avoid distortion of the audio signal if sudden level peaks occur. Technically speaking,
we refer to this reserve as “headroom” – usually this is about 10 - 20 dB (see fig.1.2). A reduction of the
operating level would allow for greater headroom, i.e. the risk of signal distortion due to level peaks would be
reduced. However, at the same time, the basic noise floor of the program material would be increased consid-
erably.
6. TECHNICAL BACKGROUND