audioguru, we all hav normal hearing (maybe u r deaf?)
No. We all do not have normal hearing and I am not deaf since I hear up to about 16kHz (pretty good for a 65 years old).
Some members here were talking about making hearing aids. Colin55 who sold 30,000 FM transmitters without pre-emphasis mentioned that he is deaf and cannot hear high audio frequencies. His FM transmitters and his hearing aid circuit produce no high audio frequencies.
We get a clear sound output from the transmitter(not like AM,telephone!) and this extremely simple circuit doesn't need ur"pre emphasis" and "Trouble boost", maybe ur transmitter sounds like an unstable AM radio or u must be deaf or cleaning ur ears may be solve ur "pre-emphasis" and "trouble boost" problems
I guess you never learned anything about FM broadcast band radio. In Google there are many sites that explain about pre-emphasis in
all FM broadcast band radio transmitters and de-emphasis in
all half-decent FM radios. Maybe you have a cheap FM radio that does not have de-emphasis.
Here is a good explanation but the demo without pre-emphasis has an error:
https://www.claessonedwards.com/index.php?option=com_content&view=article&id=72&Itemid=89 The demo without pre-emphasis also is without de-emphasis in the receiver.
In North America FM radio stations and radios use 75us emphasis which begins at 2133Hz. Without pre-emphasis then a radio with de-emphasis will produce 2133Hz at -3dB, 4266Hz will be -6dB, 8532Hz will be -12dB and 17kHz will be -18dB just like or worse than a treble tone control turned all the way down. This is worse than a telephone and about the same as a cheap AM radio.
Since your FM transmitter does not have pre-emphasis then its sound played on a normal FM radio that has de-emphasis will sound like your stereo with its treble tone control turned all the way downn, very muffled with high audio frequencies attenuated.