Volume - trying to match local FM stations

E

etorres

New member
I’m struggling to get my FM broadcast to match the volume of local FM stations. My sound quality is great minus the volume being somewhat low. I’d like to prevent people from getting blasted when they switch back to a regular station. Am I wasting my time - trying to achieve something that’s not feasible? I’ve read that FM broadcasters use dynamic compression to allow loudness. I’ve played with that on my audio files in Audacity with limited success - still never achieving the volume I'm looking for.

Here’s my hardware setup:

Pi 3 B v1.2
FPP v5.2
Soundblaster Play! 3
Signstek ST-05B set to L
Homemade dipole antenna

I’ve followed the Jason Rasmussen videos on optimizing sound. FPP volume is set to 70. My Signstek volume is set to about 11 o’clock +/-.

As I mentioned, my sound quality is great at these levels. If I push the FPP volume or the Signstek volume, I get bits of distortion on certain songs. I’ve been using The Beach Boys - Little Saint Nick as a test. At about the 9-10 second mark, the words “this time”, the “s”, “t” sounds distort if I push the volume higher than my current setup.

I’ve tried the following:
- turning up the Signstek volume
- turning up FPP volume
- stock Signstek antenna vs. mine
- removing the SoundBlaster and using the Pi’s built in sound
- setting the Signstek to H power (I knew that would have no impact but tried it anyway).

Any thoughts? I’m struggling to remember if other shows in my area had similar volume to mine…

Thanks.
 
In the radio world, you don't want to drive (input volume) a transmitter too hard as that is what usually causes distortion. You want the amplification to come from the transmitter. A tuned dipole antenna will perform better than a whip antenna. I can't help with your issue, but I can say that my EDM on the lowest setting sounds identical to local FM radio stations in quality and loudness.
 
Hmmm. OK. Thanks. I've just tried my EDM and I can get the volume to be somewhat better than the Signstek but still not quite to FM station levels without some minor clipping on the S sounds.
 
Thanks Craig, I’ll take a look. I’d like to get the volume without processing every song but I’ll check it out anyway.
 
As a broadcast engineer, let me say a few things.

1. Commercial stations compress the living Jesus out of their audio to compete in what is referred to as ‘the loudness war’. It is so bad that they have made it so I personally can’t listen to radio because it sounds so bad.

2. They also run their modulation levels higher than they should to get even louder. A lot of them run around 120% when they should only be at 100. I only have experience with radio station transmitters, but would hazard a guess that the low powered ones easily available to us in this hobby will limit the modulation level so you can’t hit 120 and trying to will result in clipping or some form of bad AGC. Again, just a guess on that one. The manual for your says deviation of +- 75 kHz which is 100% modulation. It does not say limited to but I would guess it is.

3. Antenna will do nothing for how loud you are, only how far your coverage goes.

4. Processing your audio in Audacity or other editor will get you part way there.

5. Personal opinion as audio guy and as someone who works in the radio world. Don’t waste your time playing loudness wars with the big guys. Leave your audio alone. Anyone who stops to watch your show is in a car that is not moving and has no road noise. Leave your audio so it sounds good, not same loudness as station next to you on the dial. It will be MUCH more enjoyable for them. Loud and good sounding don’t go together on radio.
 
Thanks Shim. My goal is to get my transmission to be close enough in volume to other stations that the listener isn't blasted with sound when they tune back to a regular station. I seem to be about 80% there by switching back to my EDM transmitter and doing some minor limiting and dynamic compression on Little Saint Nick. I should probably just call it a day. I had some minor crackling on some songs this past year so I thought I'd take a crack at cleaning that up and then ran into the volume issue. I don't remember other shows being particularly quiet so I just wondered what I was doing wrong.
 
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