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Minimum phase filter
20
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
0
0.1
0.2
0.3
0.4
frequency/FS (input sampling rate)
The Minimum Phase filter is another highly regarded audio filter that
offers even lower ripple in the pass and stop bands. Unlike the Linear
Phase filter, group delay is not constant; however, phase shift is low and
the particular benefit with this filter is that the impulse response exhibits
no pre-ringing.
0
0
20
40
60
Steep filter
20
0
-20
Steep filter
-40
-60
-80
-100
-120
-140
-160
-180
-200
0
0.1
0.2
0.3
0.4
frequency/FS (input sampling rate)
Our Steep filter is a linear phase filter that has been optimised for stop
band attenuation of close-in aliasing images. Here we have traded a
little attenuation of the very highest frequency response (-2dB at 20kHz
for 44.1kHz material) and a little more pre- and post-ringing for a very
steep attenuation just outside the pass band. The Steep filter is able
to attenuate aliasing at 22kHz by some 80dB for 44.1kHz material for
instance.
Frequency response
0.5
0.6
0.7
0.8
0.9
Impulse response
80
100
120
140
160
Time (samples)
Frequency response
Linear phase filter
0.5
0.6
0.7
0.8
0.9
0
0
20
40
Note: All filters exhibit the same ultimate roll-off of approximately 140dB.
The following table shows the filter stop band attenuation for 44.1kHz
material:
1
Linear Phase
Roll-off at
-0.1dB
20kHz
Roll-off at
-10dB
22kHz
Ultimate roll-off
140dB
We encourage you to experiment with the filters to determine which
sound best to your ears and using your source equipment/programme
material. The 851D remembers and recalls the selected filter type for
each input individually, making it possible, for example, to select Steep
for the USB input and Linear Phase for Digital Input 1, and so on.
180
1
azur
851D
Impulse response
60
80
100
120
140
Time (samples)
Minimum Phase
Steep
-0.1dB
-2dB
-10dB
-82dB
140dB
140dB
160
180
13
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