In addition to my streaming station, I also have a cheap, imported (think, "Amazon") FM transmitter to listen to my station around our acreage in the country. The signal just reaches the edges of our farm.

The imported FM transmitters typically have a 50 µs pre-emphasis, which matches receivers in most of the world - but not the United States. The U.S. standard is 75 µs. The difference in pre-emphasis results in the FM signal sounding muffled in U.S. receivers with a reduction in high frequencies. I'm using the FM sound card to send a copy of the audio to the transmitter.

I've found that I can use an old, deprecated feature from Stereo Tool's FM Output, under Sound Cards, to tweak the audio back into pretty good shape: The Calibration Panel.

Using the default bands, I chose the following settings:

20 Hz: -100 dB
40 Hz: -6 dB
80 Hz: -4 dB
160 Hz: -4 dB
320 Hz: -3 dB
640 Hz: -3 dB
1280 Hz: -2.5 dB
2560 Hz: -2.0 dB
5120 Hz: -1.0 dB
10240 Hz: 0.0 dB

I didn't make any other changes to the panel. As this is my hack for a 0.1 watt imported transmitter, it may not work for anyone else. I thought I'd pass it along.

Yikes! Your gonna have little to no bass. Watch i think on youtube it's a video about removing the pre - emsphisis on 15 watt or 7 watt fm transmitters. You'd have to have the bh1415f chip though.

It actually sounds really good - I've made minor adjustments since the original post, but the filtering via the Calibration Panel works nicely. There's plenty of bass! Compared to the local commercial FM stations, my 0.1 watt signal isn't as dense, but sounds much cleaner and has far less artifacts.