7
MULTICOM PRO MDX4400
overall output signal so that no audible distortion occurs (program limiter). After the level falls below the thresh-
old, the signal returns to the original value after a period of about 1 second. This IGC circuit proves to be
extremely valuable as much for live work (loudspeaker protection) as for digital situations, where any extreme
signal peaks would exceed the maximum headroom and therefore would cause severe problems.
+
The following instructions should initially familiarize you with the special terms used, so that
you can get to know all the functions of the unit. After you have read the instructions carefully,
please put them away safely, so that you can refer to them again if necessary.
1.1 Technical Background
By employing current modern analogue technology it is possible to manufacture audio equipment with a
dynamic range of up to 125 dB. In contrast to analogue 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 in transmission media
and also the maximum headroom of these systems.
1.1.1 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.
1.1.2 What Are Audio Dynamics?
A remarkable feature of the human ear is that it can detect the most wide ranging amplitude changesfrom 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.
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 repre-
sents 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 headroomusually this is about 10 - 20 dB. 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 considerably.
1. INTRODUCTION
