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SOUNDHACK Spectral Shapers 1.0 (Mac/Win)

October 1, 2004

In the early 1990s, composer and CalArts professor Tom Erbe created a suite of sound-mangling software tools called SoundHack. SoundHack was unique, powerful, and — best of all — free. The software became an immediate must-have for sound designers. But all of SoundHack's processing was offline — users spent a great deal of time tapping their fingers waiting for the software to work its magic. Many of SoundHack's processes can now be carried out in real time on a well-endowed music computer. Spectral Shapers is the first of several planned plug-in bundles based on and extending SoundHack's capabilities.

Available as either a download or on CD-ROM, Spectral Shapers includes VST plug-ins for all recent versions of Windows and Mac OS, as well as Audio Units plug-ins for OS X. Other plug-in formats are currently under consideration. All four Spectral Shapers plug-ins are CPU intensive, so you'll need a fast computer to make full use of them. Using one instance of each of the VST plug-ins in Ableton Live pushed the CPU meters on a dual-processor Mac G5/2 GHz to nearly 50 percent.

Two of the four Spectral Shapers plug-ins, +spectralgate and +spectralcompand, are dynamics processors. The third plug-in, +morphfilter, uses a tempo-syncable LFO to morph between two filters. The fourth plug-in, +binaural, uses filters that simulate the filtering effect of the head and outer ear to create LFO-driven surround panning. I'll start with a look at the dynamics processors.


+spectralgate and +spectralcompand use a technique called Fast Fourier Transform (FFT) to divide the audio that is being processed into 513 frequency bands. Separate dynamic processing is then applied to each band, and the bands are recombined to produce the output. You have control over several global parameters (covered later in this review), as well as the threshold level at which processing is applied for each band. You set the threshold curve either by analyzing the audio being processed or by drawing in the plug-in's frequency display with the mouse.

The red curve in the central portion of the +spectralgate control panel is the threshold curve (see Fig. 1). In this case, however, it was not drawn in. Instead, I used +spectralgate's Learn function to capture the frequency spectrum of a guitar loop, and I used that as the threshold shape for dynamic ducking of a drum loop. Web Clip 1 illustrates the process, beginning with the guitar loop, which is followed by the unprocessed drum loop, which is then followed by the processed drum loop.

+spectralgate offers two dynamic processes: gating and ducking. Both of these processes involve changing the level of the audio being processed by the amount set by the Gain knob. The change can be positive (raising the level) or negative (lowering the level). The difference between gating and ducking is that gating applies the level change only when the signal level of the affected band is below the threshold, whereas ducking applies the level change when the signal level is above the threshold. Because of the large number of bands, when the threshold shape is captured by analyzing another audio clip, the process transfers some of its spectral characteristics to the processed audio.

You don't need to set the threshold shape by capturing the spectrum of an audio clip. You can draw in your own shape, even a simple straight line, which will produce a 513-band noise gate that affects only those bands below the fixed threshold, as indicated by the straight line.

The +spectralcompand plug-in is similar to +spectralgate, but it offers compression and expansion instead of gating and ducking. Like ducking, compression is applied when the signal level is above the threshold, but the level is scaled rather than simply offset. The gain setting is replaced by a compression amount setting. Like gating, expansion applies when the signal level is below the threshold, but again the level is scaled rather than offset. The results tend to be subtler and smoother.

All the Spectral Shapers plug-ins have a minimum number of controls, with significant thought given to what controls will produce the maximum impact. Almost all tweaks produce a noticeable effect. All knobs are linear and have a large readout. You can't manually type in values, however, and the knobs are difficult to adjust at a high resolution. Plans for a modifier-key option for fine adjustments are in the works.

+spectralgate and +spectralcompand have Threshold and Tilt controls for adjusting all thresholds simultaneously. Tilt adjusts the thresholds for high bands in the opposite direction as those for low bands, allowing you to tilt the effect toward one end of the frequency spectrum. The Attack and Release controls let you determine how quickly the effect turns on and off once the signal crosses the threshold. The range is 0 (instant) to 1 second in 100-millisecond increments. A Gain control lets you compensate for overall level changes. +spectralgate also has an Autogain feature, which maintains unity gain by automatically adjusting the Gain control on the fly.


The third plug-in, called +morphfilter, morphs between two 513-band filters. As with the dynamics processors, you can draw in the filter shape or analyze incoming audio to capture its frequency spectrum. Unlike the dynamics processors, +morphfilter displays a shape that actually represents the filter's frequency spectrum (meaning the gain change for each band) rather than the threshold levels beyond which the gain change is applied. The difference is subtle, and you also can use the dynamic processors to sculpt one sound based on the harmonic content of another. Only +morphfilter, however, can morph between two spectra.

You can control morphing manually using a control-panel knob, remotely using MIDI to automate the knob, or automatically using +morphfilter's built-in LFO. The LFO rate ranges from 0 (off) to 4.0 Hz in increments of 0.1 Hz, but an accompanying LFO Divide control can split the LFO frequency by an integer between 1 and 11. Dividing the lowest LFO frequency by 11 results in an approximately two-minute LFO cycle. The LFO can be synchronized to the host's tempo, but in that case the fastest rate is one LFO cycle per beat; in other words, the LFO can go very slow but not very fast.

One of the more interesting uses for +morphfilter is to apply the spectral characteristics of one or more harmonically rich sounds to a relatively neutral sound. I created Web Clip 2 by capturing the spectra of different- pitched guitar and string pads and applying them to a noise burst recorded in a stairwell (see Fig. 2).

Another interesting characteristic of +morphfilter is its ability to invert the spectrum of the applied filter. Processing a sound with the inverse of its own spectrum tends to flatten the sound's spectrum. Beyond simply reversing the spectrum, you can actually vary the amount of filtering continuously from -2.0 to 2.0, with 1.0 representing the filter exactly as drawn. Together with the Tilt control (which operates as it does in the dynamics processors), inversion gives you a dramatic range of coloring options.

The fourth Spectral Shapers plug-in, +binaural, uses filtering to implement surround panning. It allows you to place the sound at any position around the head at the same elevation as your ears. (Elevation control is planned for a future version.) The +binaural plug-in is most effective when used with headphones, but it is also effective when used with speakers.

Unlike the other Spectral Shapers plug-ins, you do not set up +binaural's filter shapes; it uses predefined filters that simulate the filtering effect of the head and outer ear at all angles. Two different filter models are provided; you can select the model to use and the position (in degrees from 0 to 360) to simulate.

+binaural has an LFO similar to +morphfilter's for automating the position. You can influence +binaural's LFO shape by means of a two-dimensional envelope editor that represents the LFO value (vertical) at eight time positions (horizontal). When you click in the editor, the closest of the eight points jumps to the cursor position. It's not terribly elegant, but it does provide you with some control over the panning automation.


Spectral Shapers is an interesting and useful bundle of filter plug-ins. I don't know of any other plug-ins that perform the same exact functions as those of Spectral Shapers. The user interface is well thought-out, although the controls are somewhat limited in range and resolution. The documentation is clear, but it lacks many examples. The ticket here is clearly experimentation. If you're looking for something to spice up your DSP toolkit, Spectral Shapers is definitely worth a look.

Len Sasso is an associate editor of EM. He can be contacted through his Web site at

Minimum System Requirements

Spectral Shapers 1.0

MAC: G3/500; 256 MB RAM; Mac OS 9 or OS X

PC: Pentium II/500; 128 MB RAM; Windows 98/XP


Spectral Shapers 1.0 (Mac/Win)
effects plug-in bundle
$150 CD-ROM; $125 download



PROS: Unique DSP effects. Excellent sound quality. Lots of room for creativity.

CONS: Knobs difficult to fine-tune. LFO ranges are limited.


tel.: (858) 539-3933

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