FM broadcast stations use pre-emphasis to increase the deviation of high frequencies, boosting those above 2kHz-ish (North America) and 3kHz-ish (EU/AUS).  The time-constant is like the inverse of that corner frequency.  In the receiver, you have to reverse the process, to get back to a flat frequency response.

Think of it like progressive treble boost on transmit, then treble reduction on receive.  It's all about getting best signal to noise ratio.  Similar processes are using on vinyle records (RIAA curve)

Whether to select 75 or 50 depends entirely on what the WBFM stations you are receiving as using, so 75 should be good for your region.

Try swapping it while listening to a high-quality classical music channel and you might hear the difference.  Speech and compressed electronic music might not form the best test signal for comparison!

https://www.claessonedwards.com/bafm-tech/bbp-preemph-fm

Neil G4DBN

On 22/06/2019 18:51, robert ross wrote:

Hi Bill;

     WHAT EXACTLY IS…"Demod Settings, De-emphasys time constant” ??  I see mine was set to 50us, so I changed it to 75us as you suggest. What does that actually do?? Is this gonna work even better now that I have changed it to 75us?? Why is it different for USA and the World. I assume CANADA is the same as USA…since I am in CANADA.

Thanks for any insight on this Demod Settings, De-emphasys time constant adjustment.

Regards..ROB VA3SW

Robert Ross

London, Ontario CANADA

On Jun 22, 2019, at 13:12, Bill Nollman <billct97@...> wrote:

 

If you are in the US you also need to set the WBFM de-emphasys for the US.

SET, Demod Settings, De-emphasys time constant – set the dropdown to 75us for the US, 50us for the rest of the world, OK.

 

Enjoy!

Bill