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Analogue Solutions Filtered Coffee

Analogue Filter Module
By Paul Ward


Despite the prevalence of digital processing, stand-alone analogue filters continue to have an important part to play in modern production. It's no surprise to find Analogue Solutions releasing one — but the low price might cause a few raised eyebrows...

The Filtered Coffee is the latest addition to the Phobos range of music machinery from UK-based Analogue Solutions, one of the current keepers of the analogue flame. Current Phobos products include the Black Coffee synth, the Oberkorn sequencer (reviewed SOS September 2002) and the Vostok suitcase synth, all of which are fundamentally analogue devices — and why not indeed? True analogue synthesis and sound processing continues to survive and thrive, despite the onslaught of digital technology and computer-based processing plug-ins.


The Filtered Coffee is an analogue filter and VCA unit in a standard 1U 19-inch rack format, and all of its connections are analogue, presented on standard quarter-inch jack sockets (see the 'Round The Back' box towards the end of this article). Front to back, it measures a mere 13cm or so, which may help if you are short of rack depth. On the other hand, this can be a right royal pain if you need to house it between deeper rack boxes, when cabling can become extremely difficult — I speak from bitter past experience of similarly sized units! An external power supply is required, which Analogue Solutions include with the device. This is of the all-too-familiar wall-wart type upon which I continue to heap my disdain at every opportunity! The 15V AC, 500mA supply is fairly unusual compared to the more common 9V stomp box variety, so I'd suggest potential live users do themselves a favour by buying a backup before the inevitable happens and they can't find a replacement at short notice.

The fundamental filter design in the Filtered Coffee module is based on that found in Korg's vintage MS20 monosynth. This was a 12dB-per-octave filter that managed to exhibit a character of its own that was to the liking of many musicians, despite not having the aggressive power of a 24dB-per-octave filter. In fact, the Filtered Coffee contains a pair of resonant filters, a high-pass and a low-pass, arranged in series, with the high-pass placed first in the signal path. The filters can each be used in isolation (or their order in the signal path reversed) by tapping into the signal chain via the appropriate audio in/out sockets on the rear. I found the arrangement of the controls to be a bit problematic: both Cutoff knobs are placed together in the centre of the control panel, whilst the Resonance controls are placed to the outer edge of each filter block. Throughout the time I was working with the Filtered Coffee, I never grew comfortable with this arrangement, and had to continually check the legending with each turn of a knob.

Are You Following Me?

Input signals passing into the Filtered Coffee are first routed into an envelope follower, with attendant Sensitivity control. The envelope follower supposedly provides a control voltage that can then be applied to the Filtered Coffee's low- and high-pass filters and its VCA. I was disappointed, however, by the device's lack of simple envelope controls; having the envelope follower on board is really no substitute. I found setting the level for the follower to be a very hit-and-miss affair — on some drum loops it just seemed impossible to arrive at anything that would suit the changing signal level across a number of bars. When sending simple synth lines into the unit, the level shift caused by two beating oscillators confused the envelope follower and no amount of tweaking left me with a consistent result. Fundamentally, there is no ability to override the shape of the incoming amplitude envelope. Feeling that many users would find this a significant limitation, I contacted Analogue Solutions. The company claim to have subsequently improved the sensitivity and envelope timing on new models, but I had no opportunity to test this claim for myself before this review went to press, so try one and see how you get on with it!


A pair of LFOs is provided, with speeds ranging from one cycle over around 20 seconds to about 20 cycles per second (unfortunately, the manual does not specify exact frequencies), producing fixed triangle-wave shapes.

Each filter has a pair of CV inputs that are dedicated to cutoff modulation duties. CV1 can be switched between LFO1 or the (rear-mounted) CV pedal input. CV2 routes either the CV from the envelope follower, or LFO2. For the low-pass filter, pulling either the CV1 or CV2 knob out inverts the control voltage, while the high-pass has this pull-out invert option on CV2 only. Both switches have a third centre position, which simply switches the CV signal off — a very useful feature when setting up patches.

The input level from the high-pass filter into the low-pass filter can be attenuated, but not boosted. The design also allows a signal to be plumbed straight into the low-pass filter from a direct input on the back panel, bypassing both the high-pass filter and envelope follower.

The final stage of the Filtered Coffee is the amplifier. VCA level may be modulated by LFO2 (positive or negative), or the control voltage derived from the envelope follower. Both modulation sources share the same level control. Further options include the ability to hold the VCA open and to remove either modulation source from controlling the VCA. An overall in/out switch is available for comparing the original signal with the processed sound.

Filter resonance on both the high- and low-pass filters goes all the way into self-oscillation. I have used a Korg MS20 in the past, so am fully aware of how good that filter can sound. Whilst lacking the fruitiness of a Moog filter, and the gritty edge of other classic filters such as those employed by Sequential Circuits or Roland, the MS20 always managed to somehow sound appealing. For me this has much to do with the filter's ability to apply bucket-loads of resonance without losing the source signal's low-frequency content — there are very few analogue filters that manage this trick quite so well. This is of crucial importance in a filter designed to handle considerably more than a few simple, static synth waveforms. Drum and bass loops emerge with most of their punch intact despite any amount of high-frequency mangling that has gone on during their passage through the low-pass filter. If, on the other hand, you do need to tame any low frequencies, then the high-pass filter will be happy to oblige.

The sound-mangling potential of the Filtered Coffee doesn't end there, however — the audio input can also be overloaded for a distorted sound, which produced some excellent results with the signals I threw at it. I found it gave a very rich, warm result, fattening and thickening my input signals in a very appealing manner. I also patched it across the output of my Minimoog and was very impressed by the way I could push the signal into warm distortion without anything becoming unduly 'fizzy' or harsh. The resonance can be turned up high enough to add further distortion too!

The most fun I had with the Filtered Coffee began when I plugged a CV pedal into the back — I can see a lot of folks wishing this socket had made it around to the front panel! A few easy tweaks, and 'Theme From Shaft' was blurting from my studio monitors — or at least it would have been if I could play guitar (I had to content myself with a few vague stabs from a funk guitar sample CD!). Once again, I fed some of my analogue synths, their own filters wide open, into the Filtered Coffee and was very pleasantly rewarded with some funk-laden bass lines that would grace the grooviest of grooves. As a dedicated wah-wah pedal, the Filtered Coffee may seem overkill, but after introducing a couple of guitarist friends to this module, I think it could well find some sales in that direction!

The Filtered Coffee is a mono device, although a second machine can apparently be synchronised by sharing envelope follower and LFO control voltages via link cables. Two machines linked in this way would be capable of some complex panning effects coupled with in-phase/out-of phase filter sweeps (by way of the CV invert controls). It's an interesting idea, but I had only the one machine for review, so I can't comment on how well it works in practice.


All round, the Filtered Coffee is a bit of a mixed (tea?) bag. As a stand-alone filter, I believe it has some drawbacks; the addition of a trigger input (CV or MIDI) and some simple envelope controls, to name a couple of suggestions, would widen its appeal greatly. Anyone with a suitable control voltage source to apply to the CV inputs would benefit most, since it would free them from the vagaries of the envelope follower. However, the filter certainly sounds very good indeed, taking all signals in its stride and sending them back out into the world all the better for the experience, and the price is keen compared to most other stand-alone filter modules. I can certainly vouch for the power and warmth available here, so if you're unfazed by the problems I experienced with the envelope follower and/or have the CV gear needed to circumnavigate the problem altogether, then I can recommend it.

Comprehensive Connectivity


There's a generous amount of connectivity potential around the back of Filtered Coffee. The available connections are as follows:

  • Signal in.
  • Signal thru.
  • Env CV out.
  • Pedal CV in.
  • Pedal CV out.
  • LFO1 CV out.
  • LFO2 CV out.
  • High-pass filter cutoff CV in.
  • High-pass filter signal out.
  • Low-pass filter (and VCA) signal in.
  • Low-pass filter cutoff CV in.
  • VCA signal in.
  • VCA CV in.
  • Signal out.

(All CVs in the range ±12 Volts.)


  • Rich, warm analogue high-pass and low-pass filtering.
  • Filter retains low-frequency content even at high resonance settings.
  • Two LFOs.
  • CV pedal input.
  • Lots of physical connection options.
  • Overdriving the input can produce great-sounding distortion.


  • Lack of triggering and envelope controls.
  • Strange positioning of control knobs.
  • External power supply.


The Filtered Coffee sounds wonderful, but is somewhat lacking in control options, especially for envelope shaping. Filter/distortion characteristics, connectivity options and CV pedal input are the highlights of this device, and may well be enough to make it a winner.


£199 including VAT.

Analogue Solutions +44 (0)1384 353694.

Published August 2002