Trident Audio Hi-Lo 500-Series Tracking Filters

The Hi-Cut

This is a sweepable low-pass filter with unity gain in the selected passband and a selectable (12 or 24 dB per octave) roll-off outside the passband. The cutoff frequency can be set from 75 Hz to 24 kHz.

In addition, a Resonance control can be switched into circuit, to introduce a resonant peak at the selected cutoff frequency. The size of this peak, which is dependent on the elected frequency selected on the front panel, can be varied from zero to approximately +12 dB. A Hi-Cut Enable switch allows each individual frequency band or filter to be assessed, while a red Peak warning indicator will illuminate at around +16 dBu, approximately 12 dBu below clipping.

The Lo-Cut

This is a sweepable high-pass filter with unity gain in the selected passband and selectable (12 or 24 dB per octave) roll-off outside of the passband. The cutoff frequency can be set manually, anywhere from 15 Hz to 16 kHz.

In addition, a Resonance control can be switched into the circuit, to introduce a resonant peak at the selected cutoff frequency. The size of this peak, which is dependent on the elected frequency selected on the front panel, can be varied from zero to approximately +12 dB. A Low-Cut Enable switch allows each individual frequency band or filter to be assessed, while a red Peak warning indicator will illuminate at around +16 dBu, approximately 12 dBu below clipping.

Dynamic Tracking

Using the Track Signal function, enables the Lo-Cut or Hi-Cut filter to be used for a dynamic hum and rumble reduction (Lo-Cut) or general noise reduction (Hi-Cut). This is a technique that relies on the psychoacoustic effect of masking, in which a louder signal will cover up a quieter signal of the same frequency. In this mode, the cut-off frequency dynamically tracks the low- or high-frequency content of the music, with the frequency control setting the frequency to which the filter will open up in the absence of any low- or high-frequency content.

Further Filtering Possibilities

Use of higher resonant settings will result in the movement of the filter becoming audible and indeed, combined with the lower settings of the frequency control, this can be the basis of some unique special effects. The sweep range of the filters are extremely wide, from effectively subsonic/ultrasonic, right up/down to full audible bandwidth. This suggests the possibility of fading tracks in and out, not in the amplitude domain as is usual, but in the frequency domain.

Dynamic Linked Stereo Tracking

The Trident Hi-Lo module also offers the option of linked stereo tracking when paired with a second Trident Hi-Lo module. The Trident Hi-Lo provides an onboard stereo link switch (S9) for use in this instance. With both modules, stereo link switches selected to on, and the modules fitted in the pre-paired slots, the modules are now paired together.

By enabling both Hi-Lo modules Track Signal switches, and setting the frequency controls to identical positions, the left and right signals are now summed together, and the automatic tracking follows both the left and right signal sources. When using a 500-Series rack with selectable stereo pairing on the rear of the rack, such as with the Trident Deca-Dent, you can release the onboard stereo link switches and both modules can be used as separate mono units without the need to access the rear of the rack.

API Radial Workorse

An onboard jumper is available for use when the Trident Hi-Lo is used in conjunction with the API Radial Workhorse. When selected, this allows the Hi-Lo to send its output to the Workhorse mix bus (pin 11), which is fed to the Workhorse mixer section. This can be used in conjunction with the onboard stereo link switch, thus enabling stereo use on the Workhorse.

Wired in Series

When two Hi-Lo modules are connected in series, slopes of 12, 24, 36, and 48 dB can be achieved, in any combination, by selecting the appropriate Slope buttons on the front of each Hi-Lo module. For example, by engaging both of the Hi-Lo modules Hi-Cut filters, and setting both modules to 24 dB slope, the program material will be subject to a 48 dB slope.

By adjusting one of the Hi-Cut filters to 12 dB, the program material will be subject to a 36 dB slope. The introduction of a third Hi-Lo in series with the first two Hi-Lo modules would provide for yet steeper slopes, again in increments of 12 dB. In fact, because they can be connected in series, you�re only limited by the number of Hi-Lo�s that you have on hand.