A Barcelona, Spain-based startup named Audio Merge is just about to meet its funding goal for a very elaborate hardware replica of the rare and coveted Altec 9069B passive variable high-pass filter. The filter is known as dub producer King Tubby’s Big Knob and is considered a legendary piece of equipment in Jamaican roots music from the 1970s and onwards. The one heard on countless releases originates from a modified MCI desk which King Tubby owned and used through his career.
Audio Merge KTBK filter
Financing the project through Ulele, Audio Merge is putting in major effort to come up with an authentic-sounding replica of the venerable filter. It’s a 3rd order variable passive high-pass filter with 10 stepped cutoff frequencies (70Hz – 7.5kHz) that was meant to remove undesired frequencies and noises from recorded material (such as dialogue). It was also used for radiophonic and spatial effects in radio and cinema sound design at the time.
While the original design from the 1960s is not very complicated, it does employ some era-specific and custom-designed components that make it harder to replicate. To that, Audio Merge made a custom multi-tap inductor coil and carefully chose off-shelf components, including capacitors and an ELMA series 04 low cut frequency switch. Additionally, the team implemented three modes to make the filter, originally designed for the time’s 600ohm impedance transfer standard, suitable for modern production. The 600ohm mode reproduces the original response, the Bell mode generates a resonance bell (controlled from a dedicated 6-step switch) over the cutoff frequency, and Notch mode is a variable notch filter.
The Altec 9069B has some recreations in both software and hardware form. Check out the Audiothing Alborosie Dub Station plug-in for a respectable shot at nailing that characteristic tone.
Price and availability
The fundraiser has almost reached its goal at the time of writing and the team wants to start shipping to 1st early bird backers in July 2021. Shipments to non early-bird backers are scheduled for November. There are several ways to back the campaign and the KTBK itself is available to order for EUR 458. That’s 10% off the regular price, which is listed as EUR 508. The price does not include shipping and taxes in your delivery destination.