An interesting thread at the antiqueradios forum...
AM Radio Pre-emphasis
https://antiqueradios.com/forums/viewtopic.php?t=440587
Macrohenry#1 · OP · 08/14/2024 12:53 pm
I've come across some interesting info I'd not thought about much, but affects all of us who listen to AM radio and particularly those of us who use Part 15 transmitters.
Seems the broadcasting industry beginning in the 40s adopted a standard preemphasis curve to boost the treble on the transmitting end...
...But Larry Langford questioned that and ran his own tests.
https://www.radioworld.com/columns-and- ... -new-curve
He concluded that a bell shaped curve sounds better on modern radios, particularly those with ceramic IF filters that practically cut off frequency response beyond about 4 kHz. His bell shaped curve would roll off treble above 4 kHz so that 10 kHz would be as the same transmit volume level as below 1 kHz....
It is the NRSC pre-emphisis curve. The Schlockwood has this and the peaking is adjustable from 3.5klz to 10klz. The manual touched on this. I am not using that so it is flat to 10klz as I have EQ with Salamandra and also bass and treble on the Schlockwood. It can be disabled or enabled with jumpers.
https://www.schlockwood.com/_files/ugd/aee96f_0d77c67166904338a73dededb75e6f7c.pdf
It is the NRSC pre-emphisis curve...
From the interlinked Radio World article:
"..The NRSC curve leaves a lot to be desired but it was well-intentioned. We all agree that despite the hype decades ago extended range radios were never built. So, the reality is the 10 dB boost at 10 kHz has little or no high-frequency impact on 99% of receivers because radios made from the most common chipset have an intermediate frequency (IF) amplifier bandpass extremely tight above 4 kHz. Efforts to ram more highs to the receiver by jacking up the HF EQ even more just results in added distortion and..."
https://www.radioworld.com/columns-and- ... -new-curve