Zebra 1.5 ($199, free upgrade) is a significantly enhanced version of Urs Heckmann's unique Audio Units (AU) synthesizer plug-in. The fixed signal path has been abandoned in favor of a modular approach using a Grid that allows virtually any combination of modules to be linked across three main signal buses and an effects bus. New modulation options have been added including two 16-stage step-sequencers called MultiStages. In addition, two new effects are introduced in the Grid: a comb-filter and delay combination and a wave shaper.

Zebra's synthesis engine is built around four multiwaveform oscillators, a variable-timbre noise source, and three multimode filters. But that description belies the complexity that is possible here. In addition to the usual analog-modeled waveforms, you can use Zebra's Spectral editor to create your own additive waveforms with individual control of 127 overtones. In a nice touch, you can combine the Spectral waveform with an inverted copy of itself. You can then vary the time offset between the waveforms either manually or using Zebra's Matrix modulation. Modulating the time offset produces interesting cancellation patterns akin to comb filtering.

Zebra offers four varieties of lowpass filter as well as standard-fare resonant 12 dB-per-octave bandpass and highpass filters. Most interesting is its formant filter, which can morph across the five vowel formants (A, E, I, O, and U) and offers control of the depth of the formant effect. Both formant morphing and depth can be modulated. You can use the MultiStages to produce speechlike effects. Download Web Clip 1 for an example.

Zebra's effects section contains three effects — delay, reverb, and a multi-effect (chorus, flange, and phase) — which can be arranged in any order and inserted in either the master output or a separate effects bus. Audio can also be routed to the send bus from Zebra's Global/Mixer module or directly in the modules Grid. One great feature of Zebra's effects is that any effect parameter can be modulated using Zebra's Matrix modulation or XY Assign features.

Got Stripes?

Zebra's oscillators, filters, noise source, and modular effects (waveshaper and comb-filter delay) are represented by graphic blocks that can be dragged to any point on the 4-column by 14-row Grid. The first three columns feed Zebra's Main, Sub 1, and Sub 2 outputs while the fourth feeds the effects bus. The outputs are mixed and enveloped in Zebra's Global/Mixer module. Setting up patches in the Grid is very simple, and there are even a couple of Scope modules that allow you to monitor the signal level at any point in the Grid.

To transfer audio between columns, Zebra provides four Line Mix modules. When one of those is activated, it can be set to route the output of the modules above it to any combination of columns. Line Mix modules can be set to merge the audio from other columns to their own column. Ring modulation of any column by any other is also built into the Line Mix modules.

Zebra offers three very powerful methods of modulating virtually any parameter of any module. First, there are built-in modulation controls for most synthesis parameters. Additionally, Matrix modulation allows you to apply any modulation source to any target and control the modulation amount by any other source. There are four Matrix modulation paths, and sources include three ADSR envelope generators, a ramp generator, three tempo-syncable LFOs, an assortment of MIDI messages, and the MultiStage step-sequencers previously mentioned.

XY Assign modulation uses four XY controls to affect any modulation target (which again means virtually any module parameter including the modulators' settings themselves). Each dimension can be routed to as many as eight different targets, each with its own range. This multitarget approach allows for extremely complex, yet often subtle modulation. A MIDI Learn function allows any dimension of any XY control to be assigned to any MIDI controller. MIDI Learn also works for most other Zebra controls, and happily, you can choose to have MIDI assignments apply globally or on a preset-by-preset basis. I set up the eight knobs on my M-Audio Oxygen 8 keyboard to control the eight XY dimensions, and then used the XY assignments for all MIDI control. In short, Zebra is a performer's dream synth.

Beast of a Different Stripe

There's no getting around the fact that Zebra is a complex synth. It takes a while to become a power user, but the manual is clear (if a bit terse), and a large collection of factory presets by a number of different authors provide great starting points for further tweaking. A run through the presets will also make it clear that Zebra is no ordinary sounding beast. You can download a time-limited demonstration of Zebra as well as a number of audio examples at www.u-he.com.

Overall EM Rating (1 through 5): 4.5
U-he.com; Web www.u-he.com