Cambridge Audio 651, 751BD user manual Filters Minimum phase filter frequency response

Filters continued

Minimum phase filter frequency response

20

0 -20

	-40
(dB)	-60
	-80
Magnitude
	-100

-120 -140 -160 -180 -200

0	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1
			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 so some time-coherence is lost; however, phase shift is low and the particular benefit with this filter is that the impulse response exhibits no pre-ringing.

Steep filter frequency response

	20
	0
	-20				Steep filter
	-40
(dB)	-60						Linear phase filter
	-80
Magnitude
	-100
	-120
	-140
	-160
	-180
	-200
	0	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1
				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 (for 44.1kHz sampled material it would be -2dB at 20kHz) 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.

Minimum phase impulse response Steep filter impulse response

Amplitude										Amplitude
0										0
				Time (samples)										Time (samples)
0	20	40	60	80	100	120	140	160	180	0	20	40	60	80	100	120	140	160	180

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 as an example:
	Linear Phase	Minimum Phase	Steep
Roll-off at 20kHz	-0.1dB	-0.1dB	-2dB
Roll-off at 22kHz	-10dB	-10dB	-82dB
Ultimate roll-off	140dB	140dB	140dB

We encourage you to experiment with the filters to determine which sound best to your ears and using your source equipment/programme material.

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