Ashly SWAMP 4-8SP Instrukcja obsługi - Strona 9
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Drukuj stronęButterworth
Butterworth filters individually are always -3dB at the displayed crossover frequency and are used because they have
a "maximally flat" passband and sharpest transition to the stopband. When a Butterworth HPF and LPF of the same crossover
frequency are summed, the combined response is always +3dB. With 12dB per octave Butterworth crossover filters, one of the
outputs must be inverted or else the combined response will result in a large notch at the crossover frequency.
Bessel
These filters, as implemented on the SP processors, are always -3dB at the displayed crossover frequency. Bessel filters
are used because they have a maximally flat group delay. Stated another way, Bessel filters have the most linear phase response.
When a Bessel HPF and LPF of the same crossover frequency are summed, the combined response is +3dB for 12dB/oct, 18dB/
oct, and 48dB/oct Bessel filters, and -2dB for 24dB/oct Bessel filters. One of the outputs must be inverted when using either
12dB/oct or 18dB/oct Bessel crossover filters or else the combined response will have a large notch.
Linkwitz-Riley
The 12 dB/oct, 24dB/oct and 48dB/oct Linkwitz-Riley filters individually are always -6dB at the displayed crossover
frequency, however the 18dB/oct Linkwitz filters individually are always -3dB at the displayed crossover frequency. The reason
for this is that Linkwitz-Riley filters are defined in terms of performance criterion on the summing of two adjacent crossover
HPF and LPF filters, rather than defined in terms of the pole-zero characteristics of individual filters. The 18dB/oct Linkwitz-
Riley individually are 18dB/oct Butterworth filters in that they have Butterworth pole-zero characteristics and also satisfy the
criterion for Linkwitz-Riley filters.
When a Linkwitz-Riley HPF and LPF of the same displayed crossover frequency are summed, the combined response
is always flat. With 12dB/oct Linkwitz-Riley crossover filters, one of the outputs must be inverted or else the combined response
will have a large notch at the crossover frequency.
4 .6e Limit
A full function compressor/limiter is included on each output channel. A limiter is commonly used to prevent tran-
sient audio signal spikes from damaging
loudspeakers, manage analog and digital
recording levels, optimize broadcast
levels, or "thicken" the sound of an
audio source (compression). The adjust-
able parameters include Limiter In/Out,
Limiter Threshold, Ratio, Attack Time,
and Release Time.
The 4-8SP lim-
iter threshold range is from -20dBu to
+20dBu. This setting determines the
signal level above which gain reduction begins, and is indicated by the yellow LED (Lim) in the output meter section. Increases
in audio level above the threshold will be reduced according to the ratio settings.
The ratio control determines the amount of gain reduction above limiter threshold. Ratio ranges from a gentle 1.2:1 to
a brick-wall INF:1. To illustrate how the ratio control works, imagine a commonly used loudspeaker protection ratio of 10:1,
which means that for every input signal increase of 10 dB above threshold, the output level will only increase by 1dB. The higher
the ratio, the more pronounced the audio effect, so use the lowest ratio possible to sufficiently address the problem.
Attack (A__ms) and Release (R__ms) settings adjust the time it takes the limiter to engage and then disengage when
the signal increases above threshold and then subsequently falls back below threshold. Attack time is adjustable from 0.5ms
through 50ms, while release time ranges from 10ms through 1s. A very fast attack time can sound unnatural, while a very long
attack time can miss some of the initial transient. Similarly, a very short release time can make the audio sound uneven, while a
very long release time can create "pumping", or "breathing" characteristics depending on the kind of signal. Experiment to find
the best solution for a given application.
Operating Manual - SWAMP 4-8SP System Processors
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