X-Stream Operator’s Manual
WM-OM-E Rev I 423
Group Delay
The delay through the filter of the lowest frequencies can be adjusted. The normal setting is 0.0%
adjustment; that is, flat response. This is used to compensate for group delay distortion before the
filter. Group delay setting is unaffected by Train Filter.
The digital implementation of our equalizing filter does not have perfectly flat group delay. The
non-flatness increases with the ratio of -3 dB frequency to sampling rate and with boost. The DDA
requires 5 samples per bit cell, which means that the -3 dB frequency will be 10% of sampling rate.
If this requirement is met, group delay should be sufficiently flat. E2PR4 is especially sensitive to
non-flat group delay. For E2PR4, especially if the "5 samples per bit cell" requirement is not met, it
will probably be beneficial to set the "Group Delay" field to a small positive number, perhaps 6% or
so. This helps flatten the group delay of our equalizer filter.
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