D.A.S. DSP-4080, User Manual

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<- Phase filter
InA Input A PHF:10
1k00Hz 150º Phase
Remember – to change filter types, press BYPASS
to bypass the filter, and then use ENTER to select the
filter type.
The phase filter has adjustable frequency, and
phase shift controls. This introduces a phase shift that
gradually changes from 180º above the centre
frequency to the specificed value at the centre
frequency, and tending towards 0º below the centre
frequency.
This graph shows the phase shift relative to the
input (ignoring processing delays), in 10 steps – the
filter will actually provide higher resolution than this,
operating in 2 steps. The filter is centred at 1kHz in
this example.
<- Low/High pass variable ‘Q’ filter (low pass shown)
InA Input A LPF:1~~\
1k00Hz Q = 3.0 LPF VarQ
Remember – to change filter types, press BYPASS
to bypass the filter, and then use ENTER to select the
filter type.
The low and high pass variable 'Q' filters have
adjustable frequency and 'Q' (or Bandwidth) controls.
The 'Q' control adjust the damping of the filter, so that
low 'Q' settings show less overshoot at the turnover
frequency, but also slower roll-off.
Remember that 'Q' is 1/Bandwidth, so the higher
the 'Q', the lower the Bandwidth, and the smaller the
range of frequencies affected. The filter is primarily
12dB/Octave, but in achieving this sort of roll-off with
a high 'Q' value will result in quite a large overshoot in
level at the turnover frequency. This type of filter is
often also called a resonant filter.
<- Elliptical filters
InA Input A HPF:1/~~
1k00Hz HP Ellip
Remember – to change filter types, press BYPASS
to bypass the filter, and then use ENTER to select the
filter type.
The elliptical filter has adjustable frequency only. This sets the 3dB point of the filter which features a
steep roll-off (of approx 36dB/Octave down to one Octave above (or below in the case of a HPF) the turnover
frequency.
However, the gain does increase again above this frequency to settle at 12dB down from 0dBr. This filter
can be used in conjunction with the standard crossover filters to produce sharper roll-offs than would be
otherwise achievable.
The use of this filter is explained in the following example.
The graph shows three different low pass filter shapes. Number 1 is a standard 24dB/Octave Linkwitz-
Riley curve. Number 2 is a 48dB/Octave Linkwitz-Riley.
As can be seen, number 2 is significantly steeper in roll-off than number 1, as would be expected.
However, number 3 is a 12dB/Octave Butterworth filter with an Elliptical Low Pass filter following it. This
produces a combined roll-off very close to that of the 48dB/Octave (with the side effect of the response rising
again after the initial drop from the pass band).
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DSP-4080
User’s Manual