Freaky Filter

If you’re in search of novel effects in Studio One, fire up the Autofilter plug-in!

Studio One’s bundled plug-ins are generally excellent, and they include a few really interesting effects. I have written before about Groove Delay and the spiffy things you can do with it. This month, I’m going to look at another space cowboy: Autofilter.

A Magnificent Pair

Envelope-controlled filters have been around for quite a while, but Autofilter has a few really nice tricks up its sleeve. (Do plug-ins have sleeves?) For a start, the Autofilter plug-in is actually two filters in one, and each filter can be set to one of seven filter types. It’s an interesting selection: Ladder (12, 18 and 24 dB/octave slopes), Analog SVF (12 and 24 dB/octave), Digital SVF (12dB/octave) and Comb. Ladder is a low-pass filter, presumably more or less modelled on the old Moog filter topology. SVF stands for ‘state variable filter’: an analogue filter topology that can be continuously varied between high-pass at one extreme to low-pass at the other, with band-pass response in the middle. Obviously, this is a plug-in, so both the Analog SVFs and the Digital SVF are digital filters, but the two use different algorithms, each of which has its own characteristics.

This slow, syrupy filter sweep sounds sort of like a flanger, but not exactly!The two filters in Autofiler can be configured serially, so that the output of filter 1 feeds the input of filter 2, or in parallel. Single Cutoff, Resonance, and Drive knobs control both filters, but the FLT Spread control applies an offset to the filter 2 cutoff frequency. These filters can sound pretty clean, but I find them most interesting when the Drive control is turned up. The Drive knob controls feedback around the filter and adds a bit of ‘analogueish’ distortion, though even at 100 percent, the distortion is fairly restrained.

This is a very flexible filter arrangement, which really comes alive when you add modulation. The Cutoff and Resonance controls can each be modulated by an envelope follower on the input and an LFO. The Cutoff and Resonance controls have separate sliders for the modulation sources. The key thing to note is that the sliders do not go from zero at the bottom to full-on at the top; they are at zero at their mid-points, and go positive or negative from there. Forgetting this little fact could leave you puzzled and frustrated.

Standard jazz drums are completely transformed by this preset that uses the 16-step sequencer for filter cutoff modulation. For something just a little less ‘out there’, bringing in a bit of the original will introduce some cymbals, which are not otherwise heard.The Envelope Length control determines how closely the envelope of the signal is followed. In practice, I haven’t yet run into a situation where this control has made a big sonic difference, but I can hear some effect. I’m sure the effectiveness of this control varies greatly depending on the source.

The LFO offers the four standard waveforms, but also a 16-step sequencer. Controlling a filter with a sequencer is huge fun, and goes all the way back to the earliest analogue sequencers controlling modular synthesizers. The LFO rate is pretty wide ranging. It can be tempo-sync’ed to any value from 1/64th note triplet up to four bars, or, when not sync’ed, from 0.1Hz up to 30Hz. That’s wide enough to go from a fairly slow evolution to a low audio-frequency buzz.

Hang The Subtlety

Now, I’m sure there are some very delicate treatments you can get from Autofilter, but I’ve been concentrating on the awesome funky radical filtering effects I can get with it.

The biggest single factor in getting a sound from the Autofilter is the choice of filter types. The sound of a Ladder in series with an Analog SVF is quite different from the other way around. Putting the Ladder second gives a cleaner sound to my ear, which could be really nice for adding an effect to a delicate acoustic instrument, while putting the Ladder first feels a bit funkier, making it useful for processed vocals or synths. It’s easy to change them around, so trying different combinations to find the best one is a good way to work.

The spacing can also create radical differences in the sound all on its own. While spacing can be set over a range of ±2 octaves, I often find I get the most intense effects from values under four semitones (a major third). The resolution of the spacing control is one cent (1/100th of a semitone), and while one cent may not often produce a useful change, small amounts of 10 cents or more can make a clearly audible difference.

Let me give a few examples of the range of effects available from Autofilter.

Fake Flange

The preset shown in Screen 1 is a slow sweep that gives a little of the feeling of a thick flange, but with a different flavour. Of course, flanging is swept comb filtering, and Autofilter has a Comb filter type, so you can get even closer to a flanger if you want. For this demonstration, I wanted a very straightforward organ playing held notes, just to show how interesting Autofilter can make even a simple source. Audio example A is just the plain organ, which, as you can hear, is indeed pretty plain. Add Autofilter and you get a sweep as thick and slow as syrup, as in audio example B. This preset uses two band-pass filters set about half an octave apart; sometimes, setting values in odd relationships to each other, such as a spread of -6.37 semitones, results in more complex and interesting filtering.

This very stereo vocal process uses two Autofilter instances on bus channels. Top: the left-channel preset, with parallel filters and tempo-sync’ed modulation. Bottom: the right-channel preset, with two band-pass filters in series.I added some delay to the audio example, just for fun. Reverb adds even more texture. Autofilter can generate material that is pretty interesting bare, and gets even richer when you add further enhancement.

Perky Percussion

To show how completely the sequencer transforms a percussion track, I took one of the jazz drum loops from the content included with Studio One Professional, pasted it in four times, and added Autofilter. Audio example C is the original drums, while audio example D is the processed version. The preset is shown in Screen 2.

Where the LFO was free-running for the organ, here it is sync’ed to the tempo, with a period of two bars. The filters are a low-pass Ladder cascaded into an Analog SVF that is almost, but not quite, set to low-pass. These filters are spaced less than an octave apart, and, as with the organ, in series. There is a moderate amount of Drive being applied to help remove the sound a bit more from its original form. The filter cutoff is modulated by the sequencer, while the resonance is modulated by the envelope.

Space Singing

Let’s take things a step further. I enjoy animating sounds in space so that they move around the stereo field in a less predictable way than you’d get with a standard auto-pan. I’ve created this vocal effect with two pre-fader sends on the vocal channel, feeding bus channels that each have an Autofilter.

The vocal channel fader can be all the way down, since the sends are pre-fader, but in audio example E (Autofilter_voc_example.wav), I have set the original vocal down at -30dBFS or so, panned to the centre. This is just enough to add a bit of anchoring in the centre, but not enough to undermine the intensity of the effect.

The sends to the bus channels are not panned, but the bus channels themselves are panned to opposite sides. In screen 3 you see the left channel preset on the top, and the right channel on the bottom. Notice that the left channel Autofilter is tempo-sync’ed, but the right channel is not. I find that gives the cyclic feeling of an LFO, tempered by the variation of an unrelated cycle. The two also differ in that the left channel has the filters in parallel, while the right-channel preset has them in series.

Submixing the effects channels (and, if used, the original) using another bus channel makes it easy to add a stereo compressor, if you need things nice and even. Depending on the mix, it can be interesting to leave some of the peakiness and have the vocal jump in and out a bit more.

I am also going to find out what Autofilter can do in surround, putting a signal through two Autofilters, one feeding the main left and right outputs, the other feeding a pair of rear left and right speakers; or running a signal through Autofilter and then through a phase-decoding circuit like Dolby Pro Logic 2 and putting that in surround. Autofilter is an undervalued plug-in. I recommend diving into it and just playing around, checking out its dual filters, sequencer and other delights. It’s hard to devise truly unique effects for a mix, but you can find some here.