10
Filter settings
The 651C use the WM8742 Digital to Analogue Converter (DAC) from
Wolfson Microelectronics. The 651C has two DACs in dual differential (i.e.
one per channel, in an internally balanced mode). These very high quality
parts allow a range of filters to be selected. There is no ‘right’ choice and
we encourage you to experiment with the filters and pick the one that is
best to your ears. The characteristics are shown below:
Response (dB)
Impulse Response
22kHz
Linear phase
This filter exhibits a linear phase shift (i.e. constant group delay) so that
all audio signals are time coherent, in the time domain there is a little
pre-ringing and post-ringing. Out of band rejection is good.
Steep
This filter exhibits strong attenuation of anti-aliasing images outside the
pass band (i.e. above 22.05kHz) at the expense of a little roll off at 20kHz
and some pre-ringing and post-ringing in the time domain.
Impulse Response
Response (dB)
22kHz
Minimum phase
This filter has similar out of band rejection to above but trades a slightly
non linear phase shift with frequency for no pre-ringing in the time
domain.
Impulse Response
Response (dB)
22kHz
