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Analogue Systems FB3

Filter Bank By Paul Ward
Published July 1995

Analogue Systems continue their crusade to bring pre‑MIDI devices back into studios everywhere with their new CV‑only filter bank. Paul Ward checks it out.

Arriving hot on the heels of their recently‑released TH48 analogue sequencer, Analogue System's FB3 is a 1U rack‑mounting filter module, containing three custom‑designed voltage‑controlled filters. As the company name implies, the provision of all things analogue is what these people are about and, if the FB3 is anything to go by, they do it very well.

At First Glance

The FB3 is a rather attractive device in its silver livery, and certainly seems sturdy enough to cope with the normal rigours of life in a gigging rack. A big bunch of roses is due to Analogue Systems for the proper 'Euro' mains connector, but they deserve a selection of droopy daffodils for the rear panel power switch, and a large sprig of holly up the nose for the rear‑mounted mic/line input selector! Whilst I understand the problems of trying to fit this control onto the already busy front panel, I cringe at the thought of trying to get to the back of my rack at the best of times — and I feel sure I am not alone!

All of the important action takes place on the front panel, deriving, no doubt, from this unit's roots in modular synthesizer design. The inputs and outputs are of the standard quarter‑inch jack variety, making for easy integration into a typical rig. The controls are chunky and positive, but I would have liked the legending to have been calibrated in Hz and dBs rather than the vague 1‑10 scales that have been used.

The audio input has an optimum line input level of 100 to 150 mV, making it suitable for the kind of signal one would expect from most modern synths, though microphone signals can be accommodated by use of the aforementioned mic/line switch on the rear panel. Particularly nice to see here is an overload light that will warn you if you are in danger of pushing input levels too far. 3dB of gain at the filter outputs helps to make up for any signal attenuation as a result of the filtering process.

The Filters

Each of the FB3's three parallel voltage‑controlled filters has individual knobs for cut‑off frequency and resonance. An unsuspecting sound source can be forced to pass through one, two or all three of these filters on its way to the audio outputs. Usefully, there is an overall cut‑off control, which sweeps all three filters simultaneously whilst retaining their values relative to one another. Each filter has an approximate range from 5Hz to 20kHz, and the resonance control can go from zero right through to self‑oscillation, at which point each of the FB3 filters can become a sine wave sound source in its own right.

A simple triangle wave low‑frequency oscillator (LFO) with continuously variable speed and depth controls is provided on‑board for modulating the cut‑off frequencies of the filters. A small green light blinks away cheerfully to give a useful indication of the current operating frequency. Speed is adjustable from a generous minimum of 1 cycle in 90 seconds to a rather restrictive maximum of 2 cycles per second. I would like to have seen this range extended to considerably faster rates, which would allow for those weird pseudo‑ring modulator sound effects much loved by the makers of '70s sci‑fi TV shows. The LFO also has its own CV output socket for synchronised control of another FB3, or as a control source to plug into an external synth for duties such as pitch modulation, or auto‑panning.

Further experimentation with keyboard control voltages and band‑pass filter yielded some highly usable vocoder‑type effects...

To the far right of the front panel is the socket that provides potential for the most fun with the FB3; the CV input. This is where you can plug control voltage sources, such as those from an analogue envelope generator, an LFO on a modular synthesizer, or a MIDI/CV converter that has derived a voltage from velocity or modulation wheel data on a modern MIDI synth. All three filters respond to the external control voltage simultaneously, and the depth of effect can be attenuated from a dedicated control on the FB3's front panel. The response to an external CV can also be set to a negative value, to reverse its effect on the filters. This is extremely useful where a negative control voltage may not be available from an external synth. In my own experience, I have found a combination of a low‑pass filter and a negative envelope voltage useful for creating excellent plucked sounds and evolving pads. The CV response is somewhat unusual here — it is calibrated to work on a scale of 1 volt per 4 octaves, rather than the 1 volt per octave that many vintage synths run at. In practice, this difference is not a problem, since the depth of effect can be altered from the FB3, but it's as well to be aware of it.

Four filter response types are available at the four corresponding audio outputs. The low‑ and high‑pass filters are both of the typical Moog‑ish 24dB per octave variety, whilst the notch and band‑pass filters work on a more gentle 12dB per octave. These values are sensibly chosen for a very 'musical' result, although a 12dB/24dB switch‑able option would have been nice.

In Use

The FB3's real piece of magic is that the four filter types are all available simultaneously, although they will of course take up the corresponding number of channels on your mixer. Judicious use of these outputs, combined with stereo panning, can produce some truly inspiring effects. By taking the output from both the low‑ and high‑pass filters, for example, panning the signals hard left and right on the desk, and then sweeping the filters from the LFO, I was able to create some very rich, swirling auto‑panning effects. Using band and notch filters in a similar configuration, I found myself back in 1970s territory, with Tangerine Dream‑ish sequences bouncing around the studio walls and swept string pads prompting me to brush off a few of the old Jean‑Michel Jarre chord patterns... After drafting in a couple of extra speakers and an amplifier, I was able to generate some mind‑bending quadraphonic soundscapes by using all of the four outputs. The fun only had to stop when I began to feel sea‑sick! The manual suggests synchronising two FB3s for even stronger stereo effects, but unfortunately, I only had only one unit for review. I found my own favourite uses in a more subtle approach, providing gentle notch filter sweeps to pad chords or harmonic movement to bass sequences.

The external CV is arguably the key to getting the best out of the FB3. By using an envelope voltage to create some chunky bass 'thunks' and then sweeping the cut‑off frequencies further with the onboard LFO, all manner of techno effects are available, from a notch filter sweep to liven up an otherwise static square wave to a resonant high‑pass filter squelch to add dirt and aggression to a gritty sawtooth. Further experimentation with keyboard control voltages and band‑pass filter yielded some highly usable vocoder‑type effects, particularly effective when the filtered signal consisted of vocal samples. On the subject of samples, the ones that I fed into the FB3 emerged considerably warmer and more appealing than when they entered.

The filter quality is very good indeed. I have heard warmer, more 'treacley' filters than those presented here, but they were usually on modular systems the size of a small Cornish village. I was prepared to compromise a little hiss and hum for the sake of the end result, but the FB3 proved to be a pleasant surprise, with very little in the way of residual noise. On the one occasion when I did notice some extraneous hiss, it turned out to be a bleed‑through of white noise from one of my own synths!


In the right hands, and used in conjunction with the right equipment, the FB3 is capable of producing a wide range of very desirable sounds and textures. However, you do really need a synth or MIDI/CV converter capable of producing some meaningful control voltages to make the best use of the FB3's CV input. This really restricts the usefulness of the unit to owners of modular machines (or pseudo‑modular synths, such as the ARP2600 or the old Korg MS series). For the digital synth owner looking to add a little analogue spice, the FB3 is less useful, as it can't be directly triggered via MIDI, and doesn't have its own filter envelope generator. If Analogue Systems were to complement the FB3 with a triggerable envelope generator (ideally via MIDI as well as via a trigger pulse), the unit would be usable with a much wider range of synths and sound modules.

Other items on the wish list would include individually switchable filter responses between 12dB and 24dB per octave, and another CV input. A composite output consisting of an equal mix of the four filters would be useful too, with the insertion of a jack into the separate outputs removing that filter type from the composite signal. But these suggestions would undoubtedly push up the asking price, and probably warrant another unit of rack space too.

Corrective Treatment

In addition to the various creative uses of the FB3's filters, I had a great deal of success in pressing them into corrective service. The low‑pass filter is ideal for attenuating the hiss from a noisy synth, or reducing the fizz in a DI'd guitar recording. The high‑pass filter was perfect as a means for removing low‑level mains hum, or alleviating the 'boom' from a flabby bass drum. I discovered an excellent way of adding extra 'presence' to an electric guitar solo, by mixing a band‑pass filtered version of the sound back in with the original. This technique proved similarly successful when applied to lead vocals, though the filter frequency does need to be chosen with care.


  • Wide range of analogue filter sounds in a compact package.
  • Excellent sound quality.
  • Separate, simultaneous outputs of four filter types.


  • Rear‑mounted mic/line switch.
  • Needs external CV control to achieve anything more than basic LFO sweeping effects.
  • No filter envelope generator.


A superb‑sounding bank of analogue filters that adds genuine warmth and colour to treated sounds — but only if you have a synth that can provide an envelope CV (to feed the FB3's external CV input). This unit is really designed with the serious analogue, modular synth user in mind.