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USB 7706
Compressor Dual Channel
1.2 The COMPRESSOR In Mastering
Mastering is one of the most critical processing steps in recording. During mastering, it is the goal to achieve a "maxi-
mum level" copy of the recording, without any noise or distortion. In many applications it is further required to produce
a high average volume. In the field of commercial media for example, this is apparent especially with records and cas-
settes processed with high average volumes. Quite often in these cases, however, dynamics suffer dramatically, because
the program material has been compressed and limited too heavily. Using the combined compressor and limiter functi-
ons of the COMPRESSOR allows you to increase the overall volume drastically, without audibly affecting the dynamics.
Proceed as follows:
1. Limit the dynamics of the program material by 6 dB using the limiter function. By softly clipping just the transients,
the real audio signal will not be limited, resulting in a higher headroom. The overall gain can now be increased by 6
dB, which leads to a higher volume. More that 6 dB should not be limited otherwise side effects could become audible.
2. Therefore, in addition you should also use compression. It is recommended that the compression is limited to the
"first" 6 dB of the dynamic range only. A high threshold level in the AUTO mode will generally give good results.
This effect is particularly noticeable with DAT recorders, whose level indicators achieve a response time of less than 1 ms.
Set the DAT recorder at unity and now reduce the THRESHOLD control of the COMPRESSOR until the GAIN REDUCTION
meter indicates a gain reduction of 6 dB. The "cut" signal peaks cause a reduced recording level of about 6 dB, which is
visible on the level indicators of the DAT recorder. Now increase the recording level of the recorder back to unity. The result
is a clearly louder recording without any loss of sound.
2. THE COMPRESSOR AS A PROTECTIVE DEVICE
Sound system distortion is usually a result of amplifiers and loudspeakers being driven beyond their limitations by signals
clipping. This can lead to unpleasant distortion that is dangerous to the speakers.
During normal operation a speaker diaphragm is required to accelerate, slow down, smoothly change direction and acce-
lerate again. Distorted operation (clipping) leads to instant acceleration, instant stop, change or direction and instant acce-
leration again. Since speaker diaphragms are subject to the laws of physics, they will not take this kind of punishment for
long: the diaphragm will either break up or its voice coil may overheat.
In addition to the damage caused by sustained overload, the speaker may also be damaged by an occasional high-level
overload such as, for example, the sound of a microphone falling onto a hard floor. Even if this type of transient does not
destroy a speaker outright, it may damage the speaker in such a way as to cause mechanical abrasion and future failu-
re. It is recommended that you use the compressor in order to protect your speakers. "Brick Wall" peak limiters are not
normally necessary for PA systems, as amplifiers and loudspeakers are tolerant of short signal peaks. Also, conventional
limiters have to be generally driven far beyond the headroom limit of an amplifier in order to limit the level and length of
the transients responsible for overloading the system. The disadvantage of this approach is that the unit's full range can-
not be completely used.
If you increase the average signal level by 3 dB with the compressor limiter function, you effectively double the power
amplification. In this way, for example, you can use a COMPRESSOR to convert a PA system of 5,000 Watts into a distor-
tion-free 10,000 Watts system.
The following instructions will help you to integrate the unit into your system.
2.1 Protection Of A System With A Passive Crossover
If your sound system incorporates a passive crossover network (included in the loudspeaker cabinet), insert the COM-
PRESSOR between your mixing console output and the power amplifier input.
Integrating the COMPRESSOR into a system with a passive crossover network
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