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FILTERS •
FILTERS AND CROSSOVERS
15
Low Pass
: Allows frequencies below a designated frequency to pass while attenuating those
above it. Useful for reducing overall sibilance and avoiding shrill resonant frequencies (feedback).
Low Shelving
: Boosts or attenuates frequencies below a designated frequency, leaving those
above it unaffected. The transition between the spectrum above and below the designated
frequency occurs at a fixed 6dB/octave rate. Excellent for enhancing the low-end range of a
signal.
Notch Filter
: A band-stop filter that can remove a select range of frequencies. Commonly used
for removing specific resonant frequencies from a system.
Filters for the XAP 800 are configured in G-Ware software. Refer to page 42 to see the filter
configuration window in G-Ware.
Parametric Equalizer
: A multi-band variable equalizer that allows the user to define the
amplitude of the filter, shift the center frequency of the filter, and control how wide the range is to
which the equalizer is applied. Excellent for general tone shaping or feedback removal.
The XAP 800 also features a crossover function. The crossover combines high-pass and low-pass
filters that divide a full-range signal into separate frequency ranges. These ranges can then be
sent to amplifiers and loudspeakers optimized for producing those respective frequency ranges.
Band-pass filters can be designed by overlapping high-pass and low-pass filters.
For example, the bottom end of a frequency range might be defined as 400Hz and lower. This
signal might then be heavily compressed and sent to bass bins and woofers powered by
amplifiers. The midrange (say, 400Hz to 5kHz) can be sent to full-range loudspeakers. The high
end (say, 5kHz and above) can be directed to smaller amplifiers and associated tweeters, piezos,
horns, etc.
The XAP 800 includes three types of crossovers: Butterworth, Bessel and Linkwitz-Riley. Each of
these is characterized by the steepness of their roll-off slopes (the rate of attenuation outside their
passbands). Crossovers in the XAP 800 are created by assigning the appropriate type of high-
pass filter in a processing block with the complementary low-pass filter in a separate processing
block.
Bessel Crossover
: Utilizes a low-pass filter design characterized by having a linear phase
response (or maximally flat phase response), but also a monotonic decreasing passband
amplitude response (which means it starts rolling off at DC and continues throughout the
passband). Linear phase response (e.g., a linear plot of phase shift vs. frequency producing a
straight line) results in constant time-delay (all frequencies within the passband are delayed the
same amount). Consequently, the value of linear phase that reproduces a near-perfect step
response (there is no overshoot or ringing resulting from a sudden transition between signal
levels). The drawback is a sluggish roll-off rate. For example, for the same circuit complexity, the
response for a Butterworth crossover rolls off nearly three times as rapidly.
Summary of Contents for XAP 800
Page 1: ...XAP 800 White Paper ...
Page 67: ......
