OP-X (Win, $99) and its sibling OP-X Pro (Win, $149) are excellent VSTi re-creations of the late-'70s classic synth, the Oberheim OB-X. OP-X Pro even gives you virtual trim pots emulating the touchy oscillator-tuning pots on the original circuit boards. Both soft synths faithfully reproduce many of the charming limitations of the OB-X, such as the reverse-polarity modulation lever, On/Off and Half/Full switches for mixing the oscillators, and a single Depth knob for the amount of LFO modulation applied to the filter and oscillators. If you want to know what using the OB-X was really like, these synths are a good place to start.
OP-X and OP-X Pro bring a few welcome additions to the original feature set. You can turn on the sawtooth and square oscillator waveforms simultaneously, and when both are off, you get a sine wave, which is useful for frequency modulation. OP-X Pro also features a morphing multimode filter. You can control most of the new features, such as ring, pulse-width, and filter-envelope modulation, using buttons at the bottom of the control panel that replace the original preset buttons (presets are now managed by the VST host). Another example is the arpeggiator, which is actually a cleverly implemented 6-step sequencer.
Unlike the original OB-X, the OP-X models come with hundreds of presets and are fully MIDI compatible. Although there is no MIDI Learn implementation, MIDI Control Change messages have been mapped to all OP-X parameters, and the mapping adheres closely to the Native Instruments Pro-53 mapping, which has become fairly standard. Preset banks cover classics ranging from the OB-X and other vintage synths to presets that show off the new VI features (see Web Clip 1). Native Instruments Reaktor 5 users can get a Reaktor Ensemble version of OP-X (Mac/Win, $49), and both synths are now Muse Receptor compatible. You can download demos as well as purchase the synths from Sonicprojects' Web site at www.sonicprojects.ch.