The EM Poll

Sounds in Motion

Jan 26, 2007 5:27 PM, By Jim Aikin

           

FIG. 1: Antares Filter incorporates four resonant multimode filters with delay lines and various modulation sources.

Filters are handy tools for shaping the frequency content of sounds so that they sit better in a mix. They’re also a potent resource for producing creative sound design. Filters can have especially tasty results when you use more than one, modulate the cutoff frequency, and combine them with effects such as distortion and delay. Filters can add punch to ho-hum drum loops, rhythmic activity to sustaining pads, and ethereal colors to vocals.

Filters are found in most synthesizers, but they’re also available as plug-in effects. With software such as Antares Filter or U-he Software Filterscape, you can filter a drum loop or a vocal in radical ways.

Route 66

When more than one filter is available, you can route them in series or parallel. With a series routing, you’ll hear only the portion of the frequency spectrum that passes through both filters. For instance, a lowpass filter in series with a highpass filter will produce a bandpass response. In that case, the width of the band will depend on the relative cutoff frequencies of the two filters.

Putting two lowpass filters in series and setting their cutoff frequencies to the same or nearby values will produce a steeper rolloff slope than either filter would have by itself. Be careful when cranking up the resonance of filters in series, though; when the resonant peaks are at the same frequency, the output can be quite loud.

Antares Filter (see Fig. 1) has four filters and half a dozen signal-¬routing ¬algorithms—for instance, filters 1 and 2 in series along with 3 and 4 in parallel. Web Clip 1 shows what can happen to a simple drum loop when processed by three parallel filters. If you’re using a plug-in such as Camel Audio CamelSpace, which has only one filter, you can create a series routing by using two instances of the plug-in as inserts or a parallel routing by placing the instances on aux-send channels (see Web Clip 2).

With parallel filters, panning each one to its own point in the stereo field will give the composite sound more breadth. Balancing the output amplitudes is also helpful. The ear is most sensitive to sounds in the midrange, and you can often get good results by backing off on bandpass filters that have a center frequency of around 1,000 Hz.

Hitch a Ride

When using a filter as an effect, it’s normal to modulate the cutoff frequency (and other parameters). Some filter plug-ins have step sequencers, with which you can move the cutoff in a rhythmic pattern. Synced LFOs are also good modulation sources. When using more than one LFO, I usually set the LFO rates to different rhythmic values in order to create polyrhythms. For instance, one LFO might cycle in a 3-beat pattern while another cycles every 5 beats.

An envelope follower is a great modulation source. With a drum loop as an input, the envelope follower will output a rhythmic contour that tracks the beat. Depending on the features of your audio sequencer, you may be able to input the drum loop as a sidechain and use the envelope follower to modulate an entirely different signal.

Drive, She Said

Adding overdrive distortion before a filter gives the filter more overtones to work with, which adds character to the filtered sound. By adding distortion after a narrow bandpass filter, you can pick out one element of a track (such as the ring of the snare drum) and turn it into a new rhythmic element whose character is completely different from the original sounds.

If the cutoff is being modulated by a step sequencer or synced LFO, inserting a stereo delay line after the filter will create more-complex rhythm patterns. The delay should also be synced to the master clock.

Specialized filtering plug-ins are used for exotic effects. The bands in Equo, a graphic equalizer in Image-Line FL Studio, can be morphed or used as sends to other effects. Native Instruments Spektral Delay ¬contains as many as 1,024 stereo bandpass filters—each with its own delay line. In Web Clip 3, a drum loop is turned into an audio collage, delaying different filter bands in Spektral Delay by different amounts of time.