Audio Merge releases KTBK Filter - A Passive Variable High Pass Filter

BARCELONA, Spain, May 13, 2021. We are proud to announce our first release: KTBK filter, a solution for controlling the sound tone and generating sound effects! We tried to bring the same tone as an Altec 9069B as accurately as possible to reproduce the King Tubby’s Big Knob sound. Our unit is designed to be a versatile sound effect filter for music, but also to be the first processor applying on your recordings, specially for tracking and sound editing.

We are Audio Merge, a small startup based in Barcelona-Terrassa, founded at the beginning of the pandemic by Arnau Muñoz and Xavi Lizarraga, two audio nerds and sound engineers with a demonstrated experience in music production, studio recordings, analog circuit designing, sound & music computing and music applications designing.

We aim to build analog and digital audio equipment for quality-conscious people. The Audio Merge adventure came to us when we started to work in the KTBK project. Seeing the power and the choices of our alliance to create competitive audio gear, we decided to believe in our possibilities and to struggle for our dreams. The KTBK Passive High Pass Filter is our first project and we hope it becomes the seed to build a legal cooperative structure soon, to grow up new projects.

The King Tubby’s Big Knob (KTBK) filter is a replica of the Altec 9069B, a 3rd order variable passive high-pass filter, designed during the 1960s, with 10 stepped cutoff frequencies (70, 100, 150, 250, 500, 1K, 2K, 3K, 5K and 7.5K.) that allow great control over the tone and generate sound effects with a single switch.

Our unit is adapted for modern music production with new controls for modifying the filter response and the level of the resonance bell. Besides, it is validated with DSP techniques to achieve the most accurate frequency response and we have spent some time designing our own customized multi-tap inductor coil, it is the result of our research and analyses.

The Altec unit was originally designed to reduce low frequencies on dialogue, to remove parasitic frequencies and to diminish room rumble, hum and other low frequency noises. But also as a sound effect filter used to simulate distant sounds, radiophonic voice, and other such spatial effects in radio and cinema sound design.

The KTBK filter is a replica of the Passive High Pass Filter installed on the King Tubby's MCI console, the red big button on the top right corner, Tubby’s exclusive and secret weapon, and named "Big Knob".

The components used in vintage gear such as the Altec 9069B were practically customly-made, at least the inductors and possibly the capacitors. Nowadays, We have a wide variety of capacitors and it is possible to get very similar values of capacitance. However, the multi-tap inductor is a less common element this time.

The KTBK multi-tap inductor is a customly-designed element based on various tests and analyses performed with our prototypes. We have analysed frequency and phase responses with different cores and coil winding techniques to get the most accurate cut-off frequencies.

KTBK MODES

Passive filters are very sensitive to the impedance matching. Originally, the Altec 9069B was designed to perform with a 600Ω impedance transfer standard but currently audio equipment requires other values. Our unit includes a mode control switch to be adapted to any equipment and to modify the filter behaviour.

We have implemented three MODES (not available in Altec unit) assuming the use of modern equipment:

600Ω, allows to reproduce the original HPF response.
BELL MODE, generates a resonance bell over the cut-off frequency. The bell level might be controlled with the BELL switch (right knob).
NOTCH, it is a variable notch filter, we call it VARI-NOTCH because the attenuation level and the filter bandwidth change with the frequency.

RESONANCE LEVELS

Our unit incorporates a BELL switch with 6 steps, to control the resonance bell generated over the cutoff frequency, which is also unavailable in Altec units or other clones.

CUSTOMIZED SWITCH

We have spent some time looking for a switch based on professional standards to improve the performance. The Low Cut Frequency Switch is an ELMA series 04, super smoothed, with a single twist you can cover the whole spectrum from 70 to 7.5K.

SOUND SAMPLES

If you want to hear a good demo of the KTBK filter, the best way is to listen the album we have released with Roberto Lone Ark Sanchez and Chalart58, AUDIO MERGE in DUB This is a new vinyl album composed of 10 exclusive dub productions by the most representative dub producers of our area. The album tries to give a brushstroke of the different dub styles and subgenres to show the KTBK is an indispensable tool in the studio for a dub producer;)

ALBUM PRESALE URL

KTBK CROWDFUNDING CAMPAIGN

As we are a small startup, we have prepared a crowdfunding campaign that will be active until May 29th. The KTBK filter is available with a 10% discount of retail price. We already sold out more than 20 units in two weeks. It is a campaign, only active during the month of May, and aims to raise €12000 to finance the production of the first KTBK series.

PROJECT URL: www.ulule.com/ktbk