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Sound Toys Filter Freak

Creative Filter Plug-in [Pro Tools] By Sam Inglis
Published January 2004

Sound Toys Filter Freak

Sound Toys say that their new plug-in captures the sound of an analogue filter in digital form.

Sound Toys may be a new name in the field of plug-in effects, but there's plenty of experience behind their products. Under their old name, Wave Mechanics, they produced innovative plug-ins such as Speed and Sound Blender for Pro Tools TDM systems, while developers Ken Bogdanowicz and Bob Belcher also have an impressive track record in hardware effects design, having worked on Eventide's industry-standard H3000 and DSP4000 Harmonizers.

With the change of name comes a new range of plug-ins, and a shift of focus. Sound Toys are continuing to develop exclusively for the Pro Tools platform at present, but the eight new effects announced so far have been implemented first in the host-based RTAS/HTDM format, on Mac OS 9 and OS X only. The first to appear is Filter Freak, which, as the name suggests, provides a variety of resonant filter effects, while the near future will also bring classic analogue-style phasing, flanging, echo, auto-pan and tremolo, plus the more esoteric Decapitator and Crystallizer. Sound Toys say that TDM versions of all of these should follow in the first quarter of 2003, whilst a port to other native formats such as Audio Units and VST is also being considered.

Turn On...

Filter Freak comes in the sort of circular tin box that looks as if it ought to contain old-fashioned travel sweets. A small sticker on the side informs you that you'll need a Mac running OS 9.2 or OS X, Pro Tools software, and an iLok key. However, it's not until you put the CD in the machine that you get told that a 500MHz processor is the minimum specification required to run Filter Freak. This handy piece of information isn't mentioned in the PDF-only manual, either, so owners of low-spec Macs should be careful. That said, Filter Freak's CPU consumption varies a lot depending on settings, and for the most part it was happy to run on my now-ancient 300MHz G3.

Sound Toys Filter FreakThe installer CD gives you the option to install either Filter Freak, Pace's iLok extensions, or both. Since I was already using my iLok to run several other plug-ins, I opted for the default of only installing the plug-in. However, when I started up Pro Tools, it would get as far as loading up Filter Freak before complaining that some extensions were missing and offering to connect to the Pace web site to download them. Installing the extensions as well as the plug-in from the Filter Freak CD sorted this problem out, and didn't seem to cause problems with any of my other iLok-protected plug-ins. The iLok key is authorised in the normal way using a license card supplied in the tin.

Tune In...

Sound Toys Filter FreakFilter Freak appears in the Pro Tools plug-in pop-ups in the usual mono, stereo and multi-mono versions, and an off-line Audiosuite version is also installed. When inserting an instance of Filter Freak into a track, you can choose between single-band or dual-band versions of the plug-in. I was surprised to find that the promised presets were missing on my system, but Sound Toys say no-one else has reported this problem, and they were happy to email them to me. Provided you understand the basic concepts of filtering and modulation, the interface makes it very easy to tweak the settings to your own requirements in any case.

Other modulation options include an envelope follower, user-triggered ADSR envelope, and Random S&H.Other modulation options include an envelope follower, user-triggered ADSR envelope, and Random S&H.There are three basic components to Filter Freak: the filter(s) itself, the modulation section and the input/output stage. The filter offers pretty much everything you'd expect, with a choice of low-pass, high-pass, band-pass or band-reject (notch) filter modes, and a slope variable from two-pole (12dB/octave) all the way up to eight-pole (48dB/octave). The cutoff control travels from 20Hz to 20kHz, and there's sufficient resonance available to push the filter into self-oscillation even without an input. There's also a neat graphic display which shows the shape of the filter curve, and which is animated to show the effect that your modulation settings are having on the filter.The two-band version of Filter Freak provides independent filters that can be used in serial or in parallel.The two-band version of Filter Freak provides independent filters that can be used in serial or in parallel.

The two-band version, as you'd expect, provides two separate filters which can be used serially or in parallel, with independent but linkable controls. There's still only one modulation source available, but it is possible to apply different degrees of modulation to the cutoff, resonance and output level of each filter.

The modulation section is much more sophisticated than it appears to be at first. A pop-up list provides a choice of six different modulation sources, and the interface changes to provide suitable controls for whichever of these you select. There's an envelope follower, an LFO with choice of wave shapes, a conventional sample and hold option, a 'Step' sample and hold option where a new random value is generated either by manual triggering or when the input exceeds a set level, and a manually or level-triggered ADSR envelope, but the most complex possibilities are provided by the Rhythm option (see box overleaf).

The last few controls concern the input/output stage, which is also more versatile than it seems. The first time I tried Filter Freak out on a track, I wasn't all that impressed; yes, frequencies were clearly being removed, and turning up the resonance produced the expected squelchiness, but the overall sound was a bit cold and harsh, and very easy to drive into clipping distortion. Fortunately, I soon located the switch labelled Analog Mode, and things took a serious turn for the better.

With Analog Mode engaged, ramping up the input or output levels beyond 0dB doesn't lead to clipping distortion. Instead, it generates a variety of compression and distortion effects, depending on which behaviour you select from a pop-up list. The Fat, Squash and Pump options provide progressively more obvious varieties of compression, while Dirt, Crunch and Shred offer different flavours of distortion. The colourful compression settings sounded particularly good to my ears, and I would happily use Filter Freak on a drum or bass track for this purpose alone, even if no filtering was required. Inevitably, Analog Mode requires substantially more CPU power than Digital Mode, but makes such a difference that 99 percent of Filter Freak users will probably leave it permanently engaged.

Get Rhythm

Using the Rhythm editor. You can choose the length and height of each step, but they all share a common Shape... Using the Rhythm editor. You can choose the length and height of each step, but they all share a common Shape... Filter Freak's Rhythm generator is, in essence, a kind of step sequencer for modulating cutoff, resonance and output level, and can be run at a user-specified tempo or sync'ed to Pro Tools's Conductor track using MIDI Beat Clock. A Filter Freak Rhythm is composed of steps at up to 32nd-note resolution, each with its own level and duration settings, with a user-specifiable number of beats and bars. A Groove control imposes different amounts of shuffle or swing feel to the Rhythm, and you can also specify how the duration of each Filter Freak Rhythm relates to musical measure in Pro Tools, which can lead to interesting results — mapping a busy sequence to a 32nd-note measure, for instance, produces a rapid-fire sort of burbling modulation.

...which is defined in the Shape editor. With the Smoothing control at zero, the lines are flat; as you turn it to the right, it shapes the curve according to the behaviour you choose with the Mode control. ...which is defined in the Shape editor. With the Smoothing control at zero, the lines are flat; as you turn it to the right, it shapes the curve according to the behaviour you choose with the Mode control. A range of presets is provided, and you can customise any Rhythm in a pop-up editor window which displays the Rhythm as a green line, plotted against a grid. To add a new step to the Rhythm you simply click in a blank area of the grid. Clicking and dragging with the Alt key held down allows you to change the length and height of a step, the main limitation being that every step within a Rhythm has to have the same Shape. Presets include sine, square, trapezoid and up/dowm ramps, but you can also define your own Shapes in a separate pop-up editor. Here, you can modify the Shape by adding or removing points, and choosing to connect them with different types of curved or straight line. This is implemented in a slightly odd way: without any 'smoothing', the Shape is simply flat, with instant jumps from one value to the next, whilst turning the Smooth control clockwise makes the transitions more gradual.

Both the Rhythm and the Step editors take a bit of getting used to, but offer a wealth of creative possibilities. One the one hand, you can impose a complex rhythm on a static sound such as a pad; on the other, you can bring out an existing rhythm or subtly change its emphasis. Synchronisation to MIDI Beat Clock works as expected, though you can only turn it on and off in Pro Tools's MIDI menu or using automation — there's no Sync control on the plug-in interface.

I was doubtful at first as to whether two editors were really necessary, and wondered why Sound Toys hadn't gone for a more straightforward design — perhaps just allowing the user to draw in a rhythmic shape freehand on a grid — but using Filter Freak for a while made me appreciate why it works as it does. Subtle differences in Shape make a very noticeable difference in the way a Rhythm sounds, so it's very handy to be able to change the Shape of every step in one go. And if you do want to draw in modulation curves freehand, Filter Freak is fully automatable, so you could always do so in the Pro Tools Edit window.

...Freak Out

As soon as I'd found the Analog Mode switch, it became clear that Filter Freak can handle most of the traditional uses for audio filtering with ease. The long, slow filter sweeps beloved of dance producers work very nicely, with the 'analogue' input/output stage ensuring that a drum part or a complete mix still punches through even when the cutoff is screwed right down. Using the envelope follower to modulate a band-pass filter produces a mean auto-wah for electric guitar parts, while the opportunities for dirtying up a drum loop are legion. The availability of such steep filter slopes, along with a band-reject filter mode, means that Filter Freak can also be used effectively to 'kill' parts of the frequency spectrum.

You can control how much modulation is applied to the cutoff, resonance and output level of the filter(s).You can control how much modulation is applied to the cutoff, resonance and output level of the filter(s).Many people will be happy enough to have found a filter plug-in that can handle these conventional tasks with such aplomb, but Filter Freak's potential goes a lot further than that. The key elements here are the two-band filtering and, especially, the Rhythm modulation. Using these two features it's possible to radically change the characteristics of a sound, and create movement that ranges from slowly unfolding sweeps, through tight rhythmic grooves to insane burblings and bubblings. The presets provide a good demonstration of Filter Freak's potential for both conventional and off-the-wall uses.

To get a rough comparison between the sound of Filter Freak to that of a real analogue filter, I set up a heavily filtered PWM sound in my Roland Jupiter 8, then opened up the JP8's low-pass filter and fed the raw output into Pro Tools instead. A couple of minutes' experimentation with Filter Freak's ADSR envelope modulator yielded a sound that was demonstrably warmer and richer than the Jupiter's own filter, although it arguably lacked some of the latter's complexity of texture. The JP8's low-pass filter is admittedly less 'fat' than the likes of a Minimoog, but I was impressed nonetheless.

The only criticisms that come to mind are relatively minor. The HTDM version of Filter Freak has enough latency to be annoying, but that's the fault of the format, not the designers. On the 'missed opportunity' front, I would have liked to be able to trigger Filter Freak's envelope follower from another track via a side-chain, but this is hardly a major omission. With Analog Mode engaged, Filter Freak sounds irresistible, and combines instant gratification with deep and surprising creative possibilities. What more could you want?


  • Impressively rich, warm filtering in Analog Mode.
  • Output stage provides great-sounding, characterful compression and distortion.
  • Two-band filtering and complex rhythmic modulation offer a lot of depth.


  • Analog Mode adds a hefty CPU overhead, but you'll want it switched on all the time!
  • Minor anomalies with installation and missing presets in the review system.


A lot of plug-ins claim to capture the magical 'analogue' sound, but few of them succeed as well as Filter Freak.


£233.83 including VAT.

Unity Audio +44 (0)1440 785843.