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24.7.230.226
does it really have a use that makes a difference?
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without it FMwould sound tinny, much like a mag cartridge played without RIAA eq.(Maybe reversed values here but)Normal de-emphasis is set at what's referred to as 75us (microseconds). It has been from day one of FM transmission. It was always there but invisible to the user.
When Dolby FM attempted to make inroads, it required it be changed to 25us to maximize it's usefulness. That's when the switches started appearing on FM tuners and the confusion started.
Since Dolby FM pretty much went down the same path as quad, I doubt any tuners made since the late 70's still incorporate this switch.
75 usec is standard de-emphasis in North America. But in other regions it's 50 usec. Some FM tuners allow either, usually by internal wiring or a switch.Purpose is same as HF EQ in disc recording: Boost the highs at the transmitter then knock them back down in the receiver. The HF reception noise is thus greatly reduced giving quieter audio.
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