Distortion (clipping) vs squishing (multiband).

I’m just curious, what do you like most? I’m obviously talking about reasonable levels of clipping. 😛

I’m slowly building up for my pirate FM debut next summer (well, i’ve been on the air for a few months in 2008 but at very low power, bout 200mW and with an unstable transmitter, so that wasn’t much). I have finally found a car FM modulator that actually sounds nice AND has enough output to be easily amplified. It has absolutely no processing on the audio input, not even pre-emphasis. No limiting either, i can overmodulate to my heart’s desire. 😀 Noise floor is at -48dB with most of that coming from the stereo encoder. Too bad it’s not defeatable (but hey, for $11 that’s already asking for a bit too much). Anyway, it’s decent. And it takes RDS too.

The thing has a very interesting distortion pattern. At low level it’s about 2% second harmonic and then not much else. As the level is turned up 3rd and 5th harmonics go up, and 2nd actually goes DOWN. Harmonics higher than 5th only appear from the noise floor when full clipping is reached. I’ll post some TrueRTA graphs when i’ll have time to do so.

Anyway. Atm i’m using StereoTool to do the processing but i don’t really like it, it feels like a lot of features bunched together with not very much knowledge of what each of them do. Especially the multiband sucks hard, i turned that off entirely. I only use the pre-emphasis, RDS, AGC, bass boost, stereo widening, loudness and limiting.

The loudness slider is only set to 2.7dB boost as i didn’t like how it sounded at higher volume, instead i hit the modulator higher than i should. On my Yamaha T-500 tuner i peak at -1dB while everyone else peaks at -3, or MAYBE at -2 but those who peak at -2 are heavily distorted. I carefully balanced the bass boosts and the highpass filter (i worked hard to keep it no higher than 25Hz) so the tuner isn’t thrown off frequency, as the modulator doesn’t even have coupling capacitors on the audio input so it’s flat to DC! It’s kinda obvious that i’m overmodulating a fair bit and clipping some in the modulator, but this produces something i can rightfully call "that sound". You know you’re listening to THAT station. On balanced songs the clipping isn’t noticeable at all, but on tracks with heavy bass drums, the bass drum "punches thru" the rest of the sound. This is with all multiband off so i simultaneously have higher peaks and lower RMS than the rest of the stations, thus better dynamics.

And honestly, i like this sound a lot more than the multiband-heavy, bright, sibilant sound of commercial FM. Add 3-5% THD to that (since that’s how most stations here operate, and there are a couple pushing even higher levels of distortion) and you quickly realize that commercial FM sounds like ass.

Anyway, i’ll either switch back to Breakaway or build my own all-analog processing chain, since i only need highpass filtering, pre-emphasis, an AGC and a limiter, stereo widening is something i’m using just for kicks, my station will be playing mostly hip-hop so there’s no need for that. I’ll be uploading a few samples of the same song being played on a major radio and on mine, you draw the conclusions.