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576 EFFECTS MENU
the signal spectral information are maintained. The compressed portion can often be
navigated in depth simultaneously.
Both optical compressor units offer the possibility to restrict the frequency response to a
particular output. In this case a combination of high and low pass as well as shelving filters
come into play. For example, filtering lends itself to editing the side signals of basses and
lower mids in M/S mode (key word: vinyl cutting) or rather restricting the cymbals of the
percussion to the edge of the stereo field.
Sidechain: As was mentioned earlier, the sidechain signal is responsible for that which the
compressor "sees". The sidechain value is usually a smoothed middle value of the input, or
a peak. When one edits the frequency response of this signal, one rapidly changes the
relationship of the entire compressor circuit. For example, basses which are filtered out in
the sidechain can maintain controllers against unwanted pump artifacts, and in the ideal
case also increase the volume in bass-heavy pieces.
A mix of output signal at the plug-in and an external source offers additional possibilities for
sound production, especially during a mastering session when single groups are being
edited.
Master: The master section hosts one of the most important circuits of the plug-in for
sound compression and volume enhancement: the limiter. As is the case with the input,
this is combined at the output with a soft clip stage. This makes a fast reaction time or
even a look-ahead moot. At the same time, a skilled choice of limiter thresholds produces
an airy, natural, fundamental sound, even under difficult conditions and high level reduction.
Similar to the sidechain filter of the regular compressors, the limiter also provides the
possibility to remove low frequency signals from the controllers.
The limiter switch in am-munition works in two stages (see switch image). The first stage
has the primary task of extracting an envelope from the input signal. This is transferred to
the second stage in place of the actual signal which in turn forms its own envelope. Both
stages work with different parameters and provide different perceptions of the signal.
Furthermore, the first step can be switched between forwards and reverse detection. By
way of this cooperation between the stages, a very exact temporal image of the
amplification process is possible, especially with regard to difficult situations, like, for
example, bass-rich signals which should normally be compensated for, but produce
disturbing intermodulation noise with regular limiters.
The limiter circuit connects the clipping stage, and this is composed of two serial units. The
first forms a dual-band clipper together with a 2-way frequency-separating filter. The
advantage of separated clipping of basses and highs (mids, too) is a higher achievable
loudness with fewer perceivable disturbances in comparison to broadband disturbances.
This sort of disturbing intermodulation and roughening of the complete sound image can
be reduced, especially with clearly-defined bass material.
The applied frequency filter is modeled on the Linkwitz-Riley filter (4th order, 24dB/Octave,
Butterworth characteristic), the application of which can be found, among others, in
speaker construction. This produces an adequately sharp separation of bands and ensures
an exact phase length, since the bands are combined at the output. The complete phase
shift of the 2-band clipping stage amounts to 360 degrees. This should be monitored when
am-munition is used parallel to other tracks.