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TUBE COMPOSER T1952
2.1 Compression/levelling/limiting/clipping
Now that the functions of the individual sections have been clearly explained, we would like to acquaint you
with more terms and relationships of the dynamics process.
Compression
A compressor converts a large dynamic level into a restricted range. The extent of the resulting dynamic level
is dependent on the threshold, attack, release and ratio settings. As it is the desired effect of a compressor to
increase a low level signal, generally the threshold is set low. The inaudible compression mode requires fast
attack and release times and low ratios. The faster the chosen control times and the higher the compression
ratio, the greater the effect on the short term dynamics. This fact is often used to achieve audible and creative
sound effects.
Levelling
The levelling mode is used to keep output level constant, i.e. to compensate for long term gain changes,
without affecting the short term dynamics. Normally, the threshold is set quite low in order to be able to
increase low level signals. Levelling requires slow attack and release times, combined with a high ratio.
Because of the very slow response time, levelling has no effect on signal peaks or short term changes in
average level.
Limiting
The limiting function requires a fast attack time and a high ratio and release time setting, which is dependent
on the specific use and the desired sound effect. As it is usually the task of a limiter to limit only high signal
peaks, the threshold is usually set at a high level. The dynamics are reduced dependent on the ratio setting
and the degree by which the threshold point was exceeded. If the attack time is adjusted to control only the
average level without affecting signal peaks above the threshold, this is referred to as the program limiter. For
this purpose the attack time will be set above 20 ms. If the attack time is further reduced in order to also control
signal peaks, this is defined as peak limiter.
Clipping
In contrast to the two previously mentioned limiters, the clipping mode features infinitely fast control times, an
infinite compression ratio and creates an unsurpassable barrier (brickwall) for all signals above a certain level.
To be able to control the signal peaks, the clipping function radically cuts signals above the threshold, without
affecting the amplitude of the original signal. If used in normal applications, this function remains inaudible and
under certain circumstances it can even lead to an improved sound, because cutting the transients creates
artificial harmonics. If misused, clipping can cause very obvious and distasteful distortion, which in an extreme
manner, will convert the signals waveform into a square wave signal. This effect is often produced in guitar
distortion devices (fuzz boxes).
2.2 Expander/gate section
The main task of the expander/gate is to inaudibly eliminate undesirable background noise from the usable
signal. As already described in chapter 1.1.3, a downward expander automatically reduces the overall level for
all signals below an adjustable threshold. The expander therefore operates in opposite way to that of a
compressor/limiter. Expanders generally function with a flat ratio curve, so that the signal continually fades.
Noise gates, however, can be seen as high ratio expanders. If the signal falls below the threshold, it is
radically attenuated.
The BEHRINGER TUBECOMPOSER is equipped with a newly developed IRC (Interactive Ratio Control)
expander, the ratio of which is automatically adjusted dependent on the program material. The response
characteristics of conventional expanders tend to cut into the signal abruptly and the result of this is
unacceptable most of the time. Gain changes become audible.
The IRC expander is therefore equipped with a soft, interactive non-linear ratio curve, which is best suited to
human hearing. Critical signals in the vicinity of the threshold level are processed with a minute expansion
ratio, whereas signals that reduce in level will be subjected to an increasingly higher ratio, which will result in
greater attenuation.
2. OPERATION