![]() ![]() The EQ-251A featured two slide controls, each with switched frequency points. While not a graphic equalizer in today's sense, it was the forerunner. Langevin Model EQ-251A represents very early use of slide controls. Langevin, Cinema Engineering, and others, created outboard operator adjustable equalizers for post-production sound effects and speech enhancement. Telephone applications involved integrating equalization as part of the receiving electronics, as opposed to thinking of the equalizer as a separate entity.ĭuring the same period Volkman experimented with equalizers for reproduced sound, Hollywood found uses for them in producing sound. While Bell Labs used fixed equalizers earlier than this for correcting audio transmission losses, Volkman represents one of the first uses of an external variable equalizer as an added component to an installed system. He applied this new tool to equalize a motion picture theater playback system. Credit John with being the first person to use a variable equalizer to improve reproduced sound. It was the '30s and Volkman worked for RCA. Soon, some people's attention focused on just how bad these reproduction systems sounded. Motion pictures with sound brought audio playback systems into theaters for the first time. Mother Nature and Hollywood spawned the first use of variable equalizers for sound improvement. No really big histories exist regarding variable equalizer use. What types of variable equalizers exist? Why so many? Which one is best? What type of circuits prevail? What kind of filters? Who makes what? Hopefully, the answers lie within these pages, but first, a little history. Much confusion surrounds users of variable equalizers due to poorly understood terminology. Without belaboring the point too much, it is important in the beginning to clarify and use precise terminology. Variable equalizers, however, such as graphics and parametrics are very much the subject of this paper, hence the term, "operator adjustable equalizers." That is what they are - equalizers adjustable by operators - as opposed to built-in, non-adjustable, fixed circuits. Needed was a term to differentiate between fixed equalizers and variable equalizers.įixed equalizers, such as pre-emphasis and de-emphasis circuits, phono RIAA and tape NAB circuits, and others, are subject matter unto themselves, but not the concern of this survey. The term "operator adjustable equalizers" is no doubt a bit vague and cumbersome. This article presents an overview of operator adjustable equalizers in the professional audio industry. ![]() Operator Adjustable Equalizers: An Overview Dennis Bohn, Rane RaneNote 122 written 1990 last revised 8/97 ![]()
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