SOUND ON SOUND REVIEWS
SOUND ON SOUND magazine Vol.12 No.6. April 1997
Review by Chris Carter
Filters - don't you just love em? Sharp, soft, bright, dark, they each have their admirers and their uses. The current unstoppable retro renaissance shows no signs of slowing down with all the major (and many minor) players rolling out 'new retro' products monthly. With a massive international dance music scene as the current vanguard of ever more exotic filter sounds, it's not hard to see why manufacturers are keen to tap into this lucrative retro vein.
THE SHERMAN TANK
The Sherman Filterbank consists of a lot more than the name implies and is quite a package of goodies! There is pre-amp (with overdrive), two multi-mode VCF's (with selectable harmonics), an ADSR and an AR generator, an Envelope Follower, an LFO and two VCA's, It is , in essence, a synth module without an oscillator and if first impressions are any thing to go by then it the scores points as soon as you unpack it. You see a beige, sturdy looking, rack-mountable, steel unit, with colour coded rubberised knobs and bright, multi-coloured LED's. It's also compact enough, at 17" x 4.5" x 3.2", to drop into a gig bag or hold all.
The sloping front panel consists of 25 knobs and switches for controlling the various filter functions and modes. The rear of the unit contains 10 jack sockets for audio and control connections plus a MIDI in, out and three MIDI thru sockets. At first glance the myriad of knobs and LED's can look confusing but a little while spent familiarising yourself with the layout and functions and things become clear.
Working from left to right along the top row of controls, there is a single audio input and level control. This input knob also acts as a sensitivity control for triggering the ADSR/Envelope Follower and the AR generator. The input can take almost anything you care to throw at it, sampler, drum machine , Bassline, synth and guitar. The Overdrive feature is introduced by turning the input knob past its centre indent and can be adjusted from a soft harmonic type to a grungy, industrial distortion. Getting a balance between enough level to trigger the ADSR/AR and adding too much Overdrive can be a little tricky though. Next along is the FM knob, for modulating the filter. The FM depth is fed internally by the audio input but if a second source (audio signal, CV/GATE or another LFO) is plugged into the external FM input, then it can be used to modulate the VCF instead.
Next in line is the ADSR generator, similar to the type found in most synths and is very versatile and can handle short, long and inverted envelopes with ease. An LED indicates triggering and a bi-colour LED indicates whether the SUSTAIN signal is negative (red) or positive (yellow). A small switch toggles between ADSR and Envelope Follower modes. In Envelope Follower mode the ADSR control signal follows the level of the audio signal rather than just being triggered by it, with most of the controls working as in ADSR mode and the bi-colour LED acting as a level indicator by turning red when the level is too low. The ADSR/Envelope Follower can also be triggered from a socket on the rear which will accept audio or GATE signals such as percussion samples or a Bassline GATE output etc. In addition there is also an ADSR CV/GATE output socket for triggering external drum pads, sequencers and keyboards from the Filterbank.
The LFO has two control knobs, SPEED and DEPTH and produces a basic sine wave. The speed is indicated by a bi-colour LED and is adjustable from an extreme, 1 cycle per minute to 3kHz. This extends well into audio range and is great for making bubbly, ring modulator effects. The LFO depth control modulates the VCF's in anti-phase, (great for stereo), and produces a positive waveform when turned to the right and negative to the left, with a centre indent for no output
The AM input modulates the VCA's and is driven by the output of VCF 2. The result of this is a type of modulation that also varies proportionally to the amount of VCF 2 resonance. If an additional source, audio or CV/GATE, is plugged into the external AM input then a kind of rhythmic distortion can be superimposed on the sound.
Next is the AR generator, which controls the VCA's and while not as versatile as the ADSR, is capable of producing some very usable pulsing and gating effects. It is also triggered by the audio input but has an external trigger input socket that can accept audio and CV/GATE signals. The last two knobs, (before we move onto the filters) are the PARALLEL/SERIES and the BYPASS/EFFECT controls. The first allows a variable mix of the filters in either parallel (2 x 12dB) or series (1 x 24dB) or a 50% mix of both modes. The variable BYPASS/EFFECT control is a welcome change from the usual, in/out switch and allows nice smooth changes between heavily filtered effects, through more subtle effects, to a completely straight sound.
FILTERED OR PLAIN?
The VCFs are both identical 12dB types with a frequency cut-off range of DC to 20kHz and each can function as a Low pass, High pass and Band pass filter, with various combinations of all three modes.
Each VCF has a control knob for Frequency, ADSR depth, Resonance, Low/Band/High pass Balance and Mode Correction. These last two controls need some explanation. The Low/Band/High pass control is pretty self explanatory, however, the mode is fully variable and not a switched type. This allows for some nice tonal changes when sweeping the knob back and forth. The CORRECTION control is marked, -B (extreme left) to -B+LH (extreme right) and has a centre indent for no correction. An example of its function would be to set the LP/BP/HP balance control to band pass and turn the correction control right, toward -B+LH. This configures the VCF as a notch filter and produces a subtle phasing effect. VCF 1 has a separate audio output and some very extreme, swirling stereo effects can be achieved by setting the filters to different modes, in parallel.
Unlike some other filters of this type, the Filterbank refuses to go into full, self oscillation, it tries but only manages the mid/upper kHz range, so you can't produce any sub-bass sine waves that some VCF's can. But it does turn out some pretty good high pitched sweeps and warbles, very techno (and 1950's sci-fi). Just be careful you don't blow your tweeters.
Common to both VCF's is the large, HARMONICS/SYNC, 12-way rotary switch, with blue on/off LED. The first position is labelled FREE and allows both filters to run independently, while the following positions are labelled from 1 to 9 and 16. At setting number 1 both filters are in SYNC and act as a single 24dB VCF. In this mode the frequency knob and ADSR depth knob of VCF 1 control both filters. Turning the switch to the next positions (1.5 to 16), introduces progressively lower and lower harmonics until at position number 16 the harmonic content is 4 octaves lower than the original.
MIDI is included as standard and by doing this the designer of the Filterbank has expanded its usefulness ten fold and although it has a fairly basic implementation it does open up all manner of automated control options to the user. MIDI controllable functions include cut-off frequency and resonance, for each VCF, adjustable FM depth, VCA level (volume), AM depth, Attack, Decay, Sustain and Release times. MIDI can be used to trigger the ADSR and AR generators independently and the internal, audio input trigger can be turned on or off by MIDI. The Filterbank can also convert incoming audio and CV/GATE triggers to MIDI notes, from the external inputs of both the ADSR and the AR, a very useful feature indeed.
The only minus point is that the MIDI output only transmits MIDI trigger notes from the ADSR and AR and nothing else, it doesn't transmit system exclusive messages or controller information. For Cubase users, a mixer map can be supplied on request, configured for the above MIDI controllers. The current map is a little basic but does give an idea of the potential for using the Filterbank as part of a sophisticated MIDI system. Apparently, an updated version of the mixer map will be available from the Sherman web site soon.
PUNCHING AND KICKING
While this isn't the warmest analogue filter I've ever heard it certainly has a lot of character. In the upper ranges it has a pleasant 'grainy' sound, while in the middle ranges, particularly in band pass mode and with resonance, it can cut through a mix like a knife. But it's down at the bottom end where things get really serious. The affect that the harmonics switch and the overdrive has on a sound can be extraordinary, particularly if a lot of bottom end has been filtered out by the VCF. A thin and lifeless rhythm, or bass line, can take on a whole new life, with added bass punch and a kick, and then some! The Filterbank shouldn't be restricted to processing electronic instruments only. I tried feeding a guitar through the overdrive input while triggering the ADSR/VCF from a drum machine snare and triggering the AR/VCA from a high hat pattern, with the LFO adding some modulating to the VCF. The phrase 'polyrhythmic, acid funk' could sum up that sound. And of course, with MIDI control you can achieve unbelievably complex filter sweepings, ADSR triggering and VCA modulations. The Filterbank works particularly well breathing new life into samples, drum machines, digital synths, guitars and even the ubiquitous TB-303.
But beware! this unit could seriously damage your speakers and there are dire warnings concerning low frequencies printed in the manual and on the Filterbank unit, if in doubt you could use it through a compressor/limiter.
There were no noise specifications available for the review model, but I found the audio quality to be clean and noise free, even at extreme settings. However I did notice a couple of idiosyncrasies, one was a slight, but not unpleasant, instability when the filters were on maximum resonance. Another was the tendency for the volume to disappear, or suddenly jump to maximum, when sweeping the ADSR depth control, although this could have been to do with the nature of envelope generators, rather than anything being wrong with the unit.
What really sets the Sherman Filterbank apart from others in this crowded market is the additional combination of overdrive, harmonics, envelope generators, LFO, VCA's and MIDI control. While it is probably better suited to studio use than live work it will undoubtedly become required kit for many remixers, dance acts and producers, (see box). In this price range there is nothing quite like it and whether you are into retro sounding gear or not I can wholeheartedly recommend it. This is a hell of a processor! If a Moog is a Rolls Royce then the Sherman Filterbank has to be a Porsche.
ADDITIONAL TEXT/INFO BOXES
PRICE: £449 inc. VAT
UK distribution by: El Chocolate. tel/fax 0171 735 0798
Contact the designer, Herman Gillis by e-mail at: email@example.com
The Sherman Web site is at: http://www.steelpornrhino.com/sherman
Great analogue sound, with plenty of character.
Lots of innovative features with plenty of scope.
Good value for money.
Operationally, quite complex and not really suitable for the electro novice.
Quirky, non standard power supply.
No foot switch option (unless you happen to have a MIDI foot switch).
Poor instruction manual.
This is a well built, great sounding, highly specified filter, capable of some seriously extreme sound manipulation. Lots of modulation possibilities and enough interfacing to connect to almost anything you can think of. Small enough to transport easily but probably more at home in a studio than on a stage. It does have a fairly basic MIDI implementation but at this price who can complain.
The Filterbank is the brainchild of one man, Herman Gillis, and he personally checks each model before they are dispatched. It is only being produced in fairly small numbers at the moment so unfortunately you can't try one at your local music store. If you can, arrange a demo with the UK distributor, you won't be disappointed.
These are just some of the artists using the Sherman Filterbank:
Power for the Filterbank is supplied by a continental, two pin type, AC PSU, that needs an additional adaptor for UK 3 pin sockets. Unusually the PSU has a non-standard 15V AC output, not the usual DC voltage used by most manufactures. This is worrying as replacement AC to AC adaptors are near impossible to buy in your local branch of Tandy or Dixons. If I were gigging or on tour with the Filterbank I wouldn't relish losing the PSU and trying to find a replacement in a hurry.
Unfortunately the Filterbank manual is a disappointment. For a start, the title: THE ABUSERS MANUAL is a little suspect. But the real problem lies in the disorganised way it has been put together. There is no index and few meaningful specifications, but there are pages and pages of pretty pointless drawings of envelope shapes. The diagrams and examples verge on the absurd, with childish drawings of dogs, cats, mice and little men turning gears and lying in bed, used to explain complex concepts and techniques. Until it's been rewritten, forget the manual and just use the Filterbank.
Here are a few things I would like to see if Herman Gillis produces a mark 2 version:
The MIDI output to transmit controller info and system exclusive messages.
More waveforms for the LFO. CV control of the LFO and routing of the LFO to the AM modulation.
Separate controls for input level and trigger sensitivity.
Individual audio inputs for each VCF.
An Effect bypass foot switch socket, for live use.
A built in power supply.
Copyright © 1997 Chris Carter / SOS Publications.