The Orban 642B Parametric Equaliser/Notch Filter was a professional dual-channel parametric equaliser designed for creative and corrective equalisation applications where wide tonal control, precise frequency selection and deep notch filtering were required. Built as a true parametric equaliser, the Orban 642B Parametric Equaliser/Notch Filter gave the engineer independent control over frequency, bandwidth and boost or cut, with no interaction between parameters. This made the Orban 642B Parametric Equaliser/Notch Filter a highly flexible studio, broadcast and sound reinforcement tool, capable of broad tonal shaping, narrow-band problem solving, hum removal, feedback control and special effects.
The Orban 642B Parametric Equaliser/Notch Filter was designed around constant-Q equalisation. This meant that the equalisation curves were not reciprocal for a given Q, with boost bandwidths wider than cut bandwidths. Orban described this curve family as more musically useful than more common reciprocal curves, while also allowing the creation of extremely deep notches. In practice, the Orban 642B Parametric Equaliser/Notch Filter could deliver notch depths of more than 45dB, making it highly effective for suppressing hum, feedback and other interference of fixed pitch without applying broad tonal damage to the programme material.
Each band of the Orban 642B Parametric Equaliser/Notch Filter was continuously tunable over a frequency range exceeding 20:1, with the tuning ranges overlapping significantly to maximise versatility. The standard Orban 642B configuration provided one LF, one MLF, one MHF and one HF band in each channel. The LF bands covered 20Hz to 400Hz, the MLF bands covered 80Hz to 1.6kHz, the MHF bands covered 250Hz to 5kHz, and the HF bands covered 1kHz to 20kHz. Each frequency control included a vernier range of more than ±10%, allowing fast and precise fine tuning of sharp notches.
The Orban 642B Parametric Equaliser/Notch Filter provided +16dB boost and infinite cut in each band, with a typical notch depth of -45dB. The bandwidth could be varied from a broad Q of 0.29 to a sharp Q of 5.0. This gave the Orban 642B Parametric Equaliser/Notch Filter the ability to act as a broad tonal equaliser, a highly selective corrective equaliser, or a true notch filter. Narrowband dips could be made sharp enough to suppress fixed-frequency problems such as hum, while sounds rich in harmonics could be treated by using one band for each dominant harmonic.
A major operating feature of the Orban 642B Parametric Equaliser/Notch Filter was the front-panel Cascade button. In normal operation, the unit functioned as a dual 4-band equaliser. When the Cascade button was set to mono 8-band operation, the Orban 642B Parametric Equaliser/Notch Filter was reconfigured as an eight-band mono equaliser and notch filter. This was especially useful in mono reinforcement systems or any situation where a single signal required very detailed frequency correction.
The Orban 642B Parametric Equaliser/Notch Filter also included continuously tunable high-pass and low-pass filters. The high-pass filters were third-order Butterworth filters with 18dB/octave rolloff, with corner frequency variable from 20Hz to 315Hz. The low-pass filters were second-order Automatic Sliding Besselworth filters with 12dB/octave rolloff, with corner frequency variable from 2kHz to 20kHz. The low-pass response shape changed smoothly from Bessel to Butterworth rolloffs as the low-pass filter control was adjusted from 2kHz to 20kHz. These filters added further flexibility for noise reduction, passband shaping and special effects.
The operating layout of the Orban 642B Parametric Equaliser/Notch Filter was intended to be direct and intuitive. With the master EQ and band in/out switches set to in, the input level adjusted as needed, the frequency controls centred and the bandwidth controls set to 6, the unit could behave like a conventional four-knob console channel equaliser. From there, the user could increase or reduce boost and cut, adjust bandwidth and tune frequencies by ear. Broad settings produced more subtle tonal shaping, while narrow settings created a more coloured, resonant peak or a deep corrective notch.
The Orban 642B Parametric Equaliser/Notch Filter also allowed previously applied equalisation to be cancelled by setting the frequency controls to their original positions, setting the boost/cut controls to the inverse of their previous settings, and adjusting the bandwidth controls for the flattest overall response. This reflected the precision of the unit’s true parametric design and its ability to apply detailed changes in a repeatable, controlled way.
Headroom was an important part of the Orban 642B Parametric Equaliser/Notch Filter design. The overload-to-noise ratio was typically 110dB in dual 4-band mode and 101dB in mono 8-band mode, depending somewhat on control settings. Input signal gain could be adjusted from +14dB to infinite attenuation, allowing the user to match the 642B’s overload point to the overload point of the driven equipment. Overload lamps warned when the output of any internal amplifier was within 1dB of clipping, lighting for approximately 200ms when overload conditions were approached.
In recording studios, the Orban 642B Parametric Equaliser/Notch Filter could be used wherever a conventional equaliser might be used, while offering much greater corrective range and precision. It was particularly useful for cleaning up difficult tracks that console equalisers could not handle, applying broad tonal shaping, removing hum or fixed-pitch interference, creating phasing-style effects with sweeping wideband notches, or producing telephone, transistor radio and old-time recording effects by combining high-pass and low-pass filtering with controlled input overdrive.
For sound reinforcement, the Orban 642B Parametric Equaliser/Notch Filter could be used as a broadband equaliser, a notch filter, or both. Its constant-Q design helped minimise phase shift, noise build-up and ringing while dealing with room resonances and feedback. The high-pass and low-pass filters allowed the passband to be shaped so that amplifier power was not wasted feeding loudspeaker drivers with signals they could not reproduce. In mono systems, the mono 8-band Cascade configuration made the Orban 642B Parametric Equaliser/Notch Filter especially powerful as a detailed room-tuning and feedback-control processor.
The Orban 642B Parametric Equaliser/Notch Filter was designed for professional installation. The input was electronically balanced, with a load impedance of approximately 20kΩ in parallel with 500pF, and the output was balanced and floating, with 30Ω ±5% source impedance. Inputs and outputs were RFI suppressed, and the unit provided barrier strip connectors and tip/ring/sleeve phone jacks, with the chassis punched to accept optional XLR connectors. Optional balanced output transformers were also available to isolate the output stages from the driven equipment and improve RFI rejection in difficult environments.
Physically, the Orban 642B Parametric Equaliser/Notch Filter was a 2U rackmount processor, measuring 89mm x 483mm x 285mm. It operated from 115V or 230V AC, 50Hz to 60Hz, with an IEC mains connector, 3-wire grounded power cord and RFI-suppressed power input. The unit was intended for professional environments, with an operating temperature range of 0°C to 50°C and 0% to 95% relative humidity, non-condensing.
The Orban 642B Parametric Equaliser/Notch Filter remains notable as a powerful professional analogue equaliser that combined broad musical shaping with deep corrective notching. Its constant-Q architecture, dual 4-band or mono 8-band operation, continuously tunable filters, high headroom and extensive RFI suppression made it suitable for studios, sound reinforcement systems and installed audio environments where both tonal character and technical precision were required.
Features
- Full parametric operation with no interaction between parameters.
- True infinite-depth notch filtering made possible by constant-Q design.
- Each band continuously tunable over a frequency range exceeding 20:1.
- Significantly overlapping tuning ranges for increased versatility.
- Frequency vernier controls for fast and precise tuning of sharp notches.
- +16dB boost to infinite cut available in each band.
- Typical notch depth of -45dB.
- Bandwidth variable from broad Q 0.29 to sharp Q 5.0.
- Dual 4-band or mono 8-band operation selectable from the front-panel Cascade button.
- Continuously tunable 18dB/octave high-pass filters.
- Continuously tunable 12dB/octave Automatic Sliding Besselworth low-pass filters.
- Input gain adjustable from +14dB to infinite attenuation.
- Overload lamps warn when any internal amplifier is within 1dB of clipping.
- Designed for creative and corrective equalisation applications.
- Suitable for recording studios, monitor systems and sound reinforcement systems.
- Can be used for hum removal, feedback control and other fixed-frequency interference.
- Can generate phasing-style effects using sweeping wideband notches.
- Can create telephone, transistor radio and old-time recording effects using high-pass and low-pass filters.
- Electronically balanced input.
- Balanced, floating output.
- Extensive RF suppression on input, output and power leads.
- Barrier strip and TRS phone jack connections.
- Chassis prepared for optional XLR connectors.
- Optional balanced output transformers.
- Optional acrylic security cover to prevent unauthorised adjustment.