QMS does quadraphonic mid–side processing. Given a left front, right front, left back, and right back signal, it produces a mid and three side signals: left–right, front–back, and cross or diagonal. Then given these latter signals, it again produces left front, right front, left back, and right back. It has intelligent normals for passthrough, -6dB lowered mid and side signals to avoid clipping, and is equally useful for stereo mid–side when quadraphonic is not available. Rather than merely creating an image of a sound, something that you passively look at, this module allows you to create a sonic texture that fills a room. Listening becomes active exploration instead of passive observation. Ambient music is all about space. But stereo can only provide a passive experience of this space. It's like there was a wonderful landscape glimpsed from a train window, and many experiments in stereo imaging attempt to reproduce the experience of being in that train, looking through that window. With quadrophonic sonic textures, you get to leave the train and run with the caribou.
