Behringer DSP1200P - Manual (Page 32)

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times you should switch to the level meter menu where the functioning of the limiter can be monitored.
4.3.4 Expanders/noise-gates
Audio, in general, is only as good as the source from which it was derived. The dynamic range of signals will
often be restricted by noise. Synthesizers, effects devices, guitar pickups, amplifiers etc. generally produce a
high level of noise, hum or other ambient background hiss, which can disturb the quality of the program
material.
Normally these noises are inaudible if the level of the desired signal lies significantly above the level of the
noise. This perception by the ear is based on the “masking“ effect: noise will be masked and thus becomes
inaudible as soon as considerably louder sound signals in the same frequency band are added. Nevertheless,
the further the level that the desired signal decreases, the more the noise floor becomes a disturbing factor.
Expanders or noise-gates offer a solution for this problem: these devices attenuate signals when their ampli-
tudes drop, thereby fading out the background noise. Relying on this method, gain controlling amplifiers, like
expanders, can extend the dynamic range of a signal and are therefore the opposite of a compressor.
In practice, it is shown that an expansion over the entire dynamic range is not desired. With an expansion ratio
of 5:1 and a processed dynamic range of 30 dB, an output dynamic range of 150 dB will be the result, exceed-
ing all subsequent signal processors, as well as human hearing. Therefore, the amplitude control is restricted
to signals whose levels are below a certain threshold. Signals above this threshold pass through the unit
unchanged. Due to the continuous attenuation of the signals below this threshold, this kind of expansion is
termed “downward“ expansion.
The noise-gate is the simplest form of an expander: in contrast to the expander, which continuously attenuates
a signal below the threshold, the noise-gate cuts off the signal abruptly. In most applications this method is not
very useful, since the on/off transition is too drastic. The onset of a simple gate function appears very obvious
and unnatural. To achieve inaudible processing of the program material, it is necessary to be able to control the
signal’s envelope parameters. This is part of the many features of the MODULIZER PRO.
4.4 Artificial harmonics generation
By 1955 an American, Charles D. Lindridge, had already invented the first “EXCITER” (a unit that EXCITES
upper harmonics), when he presented a unit for “improving the sound of music and speech”. He enriched signal
sources with artificially generated upper harmonics and found that both sound quality, transparency and per-
ceived positioning of musical instruments could be considerably improved using this effect. He was granted an
American patent on his circuit design under the number US 2 866 849.
Compared to modern technology, Lindridge’s circuit was anything but fully developed, however, it featured
many of the aspects found in today’s modern circuit designs. Psycho-acoustic discoveries and greater knowl-
edge, gathered over the years, have allowed for new and improved circuit designs, through the use of advanced
technology.
Vacuum tubes also produce harmonics as a result of distortion caused by saturation. In general, the saturation
(overdriving) of transistor and tube-based circuits results in different types of distortion. Distortion caused by
tubes is generally considered to be more pleasant and warm, often enhancing the quality rather than deterio-
rating it. With the MODULIZER PRO various tube types and their specific sound can be emulated.
4.5 Tube technology
A closer look at developments and trends in audio technology shows that tubes are currently enjoying a
renaissance, in a time when even amateur musicians are free to use digital effects processors and recording
media, and ever more affordable digital mixing consoles are becoming a natural part of the equipment of many
semi-professional studios. The manufacturers try with ever new algorithms to get the most out of DSP’s (Digital
Signal Processors), the heart of any digital system.
Still, many audio engineers, particularly old hands often prefer using both old and new tube-equipped devices.
As they want to use their warm sound character for their productions, they are ready to accept that these
“goodies” produce a higher noise floor than modern, transistor-based devices. As a consequence, you can find
a variety of tube-based microphones, equalizers, preamps and compressors in today’s recording and master-
ing environments. The combination of semiconductor and tube technologies gives you the additional possibility
of using the best of both worlds, while being able to make up for their specific drawbacks
4. TECHNICAL BACKGROUND