The Hi-Lo is not just a filter. Trident Audio has created an analog adaptive filtering circuit for the 500 Series format.
The Trident Hi-Lo, an adaptive Hi-Cut/Lo-Cut frequency filtering module that responds dynamically to program material, providing a high degree of control and signal enhancement, unavailable in any modern-day 500 series package.
Features
- Dynamic Tracking
- Hi-Cut FREQUENCY control from 75Hz to 24kHz
- Lo-Cut FREQUENCY control from 15Hz to 16kHz
- Selectable SLOPE between 12 and 24dB
- 36dB and 48dB Slopes using 2 units wired in series
- Hi-Cut variable RESONANCE control up to +12dB
- Lo-Cut variable RESONANCE control up to +12dB
- Selectable Hi-Cut dynamic noise reduction tracking
- Selectable Lo-Cut dynamic noise reduction tracking
- Hi-Cut PEAKING indicator
- Output level PEAKING indicator
- Option for SERIES LINKING Hi-Lo modules
- Option for STEREO LINKING Hi-Lo modules
The Hi-Cut
This is a sweepable low pass filter with unity gain in the selected passband and a selectable (12dB per octave or 24dB per octave) roll-off outside the passband. The cutoff frequency can be set from 75Hz to 24kHz.
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 dependant on the elected frequency selected on the front panel, can be varied from zero to approximately +12dB. At maximum setting, RESONANCE stops just short of self-oscillation.
A HI-CUT ENABLE switch allows each individual frequency band or filter to be assessed, while a red PEAK warning indicator will illuminate at approximately +16dBu, approximately 12dBu below clipping. To allow adequate headroom, avoid boosting the signal by more than an amount which just causes this LED to flash on occasional peaks.
Hi-Cut Dynamic Tracking
Using the TRACK SIGNAL function enables the Hi-Cut filter to be used for dynamic noise reduction. 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 cutoff frequency tracks dynamically the high frequency content of the music, with the FREQUENCY control setting the frequency to which the filter will close down in the absence of any high-frequency content.
With a noisy signal applied (e.g. from analog tape or other material with a high background noise content), start with the FREQUENCY control at maximum (fully clockwise) and back off the control until the noise just disappears.
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.
Further possibilities
The sweep range of the Hi-Cut filter is extremely wide, from effectively subsonic, right up 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.
The Lo-Cut
This is a sweepable high pass filter with unity gain in the selected passband and selectable (12dB per octave or 24dB per octave) roll-off outside of the passband. The cutoff frequency can be set manually, anywhere from 15Hz to 16kHz.
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 dependant on the elected frequency selected on the front panel, can be varied from zero to approximately +12dB. At maximum setting, RESONANCE stops just short of self-oscillation.
A LOW-CUT ENABLE switch allows each individual frequency band or filter to be assessed, while a red PEAK warning indicator will illuminate at approximately +16dBu, approximately 12dBu below clip-ping. To allow adequate headroom, avoid boosting the signal by more than an amount which just causes this LED to flash on occasional peaks.
Specifications
Input Impedance 10 kilohms
Max Input +27dBu
Max Output +27dbu (Into 600ohms)
Distortion (+10dBu Out) 0.0031% (20Hz to 20kHz)
(Hi Enabled Max Freq)
(Lo Enabled Min Freq)
Distortion (+20dBu Out) 0.0069% (20Hz to 20kHz)
Frequency Response 15Hz to 60kHz (-3dB)
Noise (20Hz to 20kHz bandwidth limited)
No Filters in circuit (Residual Noise) -95dBu
High Cut Enabled
Freq Max -83.5dBu
Freq Min -90dBu
Freq Max – 24dB/Oct Slope Enabled -80dBu
Freq Min – 24dB/Oct Slope Enabled -90dBu
Freq Max – Res Enabled, Resonance Min -83.5dBu
Freq Max – Res Enabled, Resonance Max -72dBu
Freq Max – 24dB, Res Enabled, Res Max -71dBu
Freq Min – Res Enabled, Resonance Min -90dBu
Freq Min – Res Enabled, Resonance Max -90dBu
Freq Min – 24dB, Res Enabled, Res Max – 90dBu
Low Cut Enabled
Freq Max -83dBu
Freq Min -86dBu
Freq Max – 24dB/Oct Slope Enabled -83dBu
Freq Min – 24dB/Oct Slope Enabled -90dBu
Freq Max – Res Enabled, Resonance Min -84dBu
Freq Max – Res Enabled, Resonance Max -72dBu
Freq Max – 24dB, Res Enabled, Res Max -73dBu
