Stereo Tool

Yesterday I gave a presentation about Stereo Tool in Budapest (Hungary), and this morning on my way back from the airport to home I had a chance to listen to a Belgian FM station that uses Stereo Tool for their 13 FM frequencies. Now, they don't use Stereo Tool only for processing, but also to synchronize the audio between the different transmitter sites.

The setup is like this:
- There's a ShoutCast server sending out the streams
- They are received by a stream player at each transmitter site via a nationwide free WiFi network
- Stereo Tool, which runs as a plugin of that player, synchronizes the streams, performs the processing and does the stereo/RDS encoding.

Now anyone who has any experience with ShoutCast streams will probably know that they are usually not in sync at all - even if you start playback of 2 streams on the same pc they are usually multiple seconds apart. Beside that, due to small differences in sample rates between sound cards, they will start to deviate more and more, and after a few days there may be differences of multiple minutes between the different sites.

The next video shows the effect of turning the 'FM Transmitter Synchronization' in Stereo Tool on. I stopped at a parking place where I could receive 4 of the 13 frequencies.

https://www.youtube.com/watch?v=PH1mUfv ... aS&index=6

One can see that it works great!.
as this feature is set up?, there must be a synchronization between each player? Each transmitter site should be part of the same network, so that each instance is sincronize StereoTool?
 
Any information is welcome.

This is indeed great.

I suspect they send their audio uncompressed (no MP2, MP3, but PCM, WAVE) by that Shoutcast server?
Curious about the stream player and encoder (sender). We are planning to set up also something like that, but for only one transmitter.

@Edgar: MP3 stream (unfortunately), and Winamp as player with a watchdog that restarts it if it fails
Doesn't sound too 'professional' - but it works!

@nelson c: It's much simpler than you think . There's only the standard communication from the ShoutCast server to the different sites... There's no need for anything else (as you could hear). The only thing is (but that's normal with ShoutCast streams, they are TCP-based!) that there's considerable latency between the output from the studio and the sound on the transmitters. All that Stereo Tool does is to make this latency constant and the same at each site.

If you want to try it, you need to use a plugin version of Stereo Tool (I will add it to the stand alone version if I ever get to the point that I'll adding streaming functionality to it), and you need to use 'Direct sound card access'. Go to the output sound card setting and enable 'Synchronize FM signals', and set the sound card buffer size to the maximum (5 seconds, must be the same on each site!). Do that on each site and you're done. (Note: After starting, it takes a while - I think 30 minutes or so - before the audio is in sync). If there is a constant small difference left between the sites, you can fix that with the 'Extra delay' sliders. I haven't seen any instance where this is needed yet though. It might occur if you use different OS's, sound cards or PC's with very different CPU loads.

It is easier than I thought ...
Required if a player or winamp and shoutcast streaming?
I for binding studies with plants transmitters use a 193 Kbps streaming OPUS travez RadioBOSS (which supports plugins dsp) and instead of using shoutcast, use an integrated server that has the program.

Any player and any stream type should be fine.

could this be used twice for 2 redurant streaming links on the same pc in case link 1 goes down and the watchdog "switches" to link 2 ?

Yes. But the 2nd link must already have been playing for a while, and it must be (when sending out) in sync with the 1st one.