10
Filter settings
Sharp Roll-off
The 550C and 650C both use the WM8740 Digital to Analogue Converter
(DAC) from Wolfson Microelectronics. The 550C uses one stereo DAC,
whilst the 650C uses two DACs in dual differential (i.e. one per channel,
in an internally balanced mode). These very high quality parts feature a
selectable digital filter with two settings.
The sharp roll-off filter exhibits strong attenuation of aliasing images
outside the pass band (i.e. above 22.05kHz) at the expense of a little pre-
and post-ringing in the time domain.
The slow roll-off filter trades a slower roll-off and less attenuation of close
in aliasing images for less ringing in the time domain.
There is no ‘right’ choice and we encourage you to experiment with both
filters and pick the one that is best to your ears. The characteristics of
both are shown below:
0
-20
-40
-60
-80
0
22.05
44.1
0
10
20
30
40
50
60
Slow Roll-off
0
-20
-40
-60
-80
0
22.05
44.1
0
10
20
30
40
50
60
R
esponse (dB)
Impulse R
esponse
Impulse R
esponse
R
esponse (dB)
Frequency (kHz)
Time (input samples)
Time (input samples)
Frequency (kHz)
