PMix (olilarkin.co.uk; donationware), short for “preset mixer,” lets you graphically morph between presets for as many as four VST effects plug-ins arranged in series or parallel. Support for virtual instruments and AU is planned for a future release. PMix is a standalone application that accepts real-time audio input, making it a great live-performance tool. But you can use its built-in player and recorder to process audio files, and you can link pMix to your DAW for OSC and MIDI control and for audio I/O using ReWire or a third-part routing utility such as Cycling '74 Soundflower.
You start by selecting plug-ins for one or more of the four layers, and pMix is as useful for one plug-in as it is for several. You then create plug-in setups by selecting from the menu of factory presets, using the plug-in's GUI, or clicking on pMix's Random button. You add setups you like to a 2-D morphing window called the iSpace, where they are represented by circles that are color coded by layer. Dragging a layer's cursor around the iSpace morphs between plug-in settings based on the cursor's proximity to each circle. You select which parameters are affected by morphing, but pMix remembers all settings, letting you add or remove parameters from the morphing list after the fact. You can morph each layer separately or link them so that one cursor morphs all layers. Freehand or breakpoint automation curves affect the selected layer or all layers if they are linked. MIDI and OSC control of morphing is also supported.
PMix is great for simply controlling the wet/dry mix of several plug-ins — a filter, a feedback delay, and a reverb in series, for example (see Web Clip 1). Alternatively, you can completely mangle audio by radically morphing parameters such as delay time and feedback, filter resonance, pitch-shift, ring or FM modulation, and so on (see Web Clip 2). Grab pMix for effects automation that goes beyond linking up a few MIDI controllers, and you'll never look back.