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PostPosted: Mon May 30, 2022 3:21 pm 

Joined: Mon May 30, 2022 3:01 pm
Posts: 3
Hi all,

I've successfully got a Raspberry Pi 4B taking a feed over RTPL16 across the campus network for a University Radio Station I help out at (I will publish some information on doing this shortly, as I bet it will be helpful to a few people). With the default settings the processing is sounding really good, and our FM feed sounds so much better than it used to already!

However...
We were hoping to be able to configure the processing remotely using the web interface so we could better tune it to real radios and dial the output gain to not over-deviate the transmitter. This has given us a whole bunch of issues.

Firstly, when we upgraded to the latest command line version of the Rpi StereoTool, it stopped recognising our licence key when input through the command line, or the config file, or both! So we've had to revert to not using any licensed settings to stop the beeping (which is of course non-ideal after we paid for said licence).

Secondly, the web interface really doesn't seem to work that well for us when accessing it from a non-localhost address. Looking at the web inspector, the websocket seems not to want to connect at all, meaning that any attempt to tweak settings is largely pointless. I'm unable to verify for certain, but it also seems the processing may be ignoring many of the settings we gave it through the config file.

Other than this, it does seem to be working, and with the aid of ffmpeg and an extremely horrifying bash script, it has stayed on air for a while. Is it possible someone might be able to help me with the above issues? Very happy to provide .sts files and any logs as required.


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PostPosted: Tue May 31, 2022 11:08 am 

Joined: Mon Apr 25, 2022 11:19 pm
Posts: 92
I've found it helpful to get round the limitations of the web browser interface by using VNC to remote control the Raspberry Pi to make any tweaks to ST etc.

I've never tried running the command line version as I was under the impression it doesn't deal with live audio feeds, only files. I might be wrong of course! But I'm going by my initial attempts to try moving to the command line version in order to see if I can do away with the GUI/X-Windows.

So I've stuck to the GUI version since then, left minimised but with the desktop left open. If the command line can indeed deal with live audio feeds, I'd be willing to see if I can get it to work and share what I did if it's helpful for you.

Are you using the 32-bit OS or the 64-bit one? I found things run a bit smoother when I upgraded to Raspberry Pi 64-bit. It squeezes more performance out of the Raspberry Pi and even raises the CPU speed to 1.8Ghz from 1.5Ghz.

I'd also be interested to know more about RTPL16. I'd like to move the encoder Liquidsoap and web streamer Icecast2 off the ST box on to my other box which has loads of spare CPU capacity. Would RTPL16 allow me to feed the output of ST via IP to my other box, which can then encode the feed etc? If it can deal with 48Khz sampling rate, I'm in, as I encode at 320K AAC 48Khz sampling rate and also had to make sure the entire audio chain is 48Khz. Resampling not only loaded the CPU (looking at you pulseaudio!), it also ruined the sound quality.


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PostPosted: Tue May 31, 2022 11:25 am 

Joined: Mon May 30, 2022 3:01 pm
Posts: 3
You can get the command line version to work live by piping audio through it from other programs. I did consider using the jackd version with the pi, but I found the reliability of that on the pi somewhat lacking, in addition to how difficult it was to automate the connections to different sources and sinks in a startup script. (+Considering the pi's rather weak power, I thought the GUI might also be an extra overhead).

Good shout on the OS. We'd been using the 32bit version as the 64bit raspbian version didn't exist when we installed the transmission system, but doing a brief bit of reading you're clearly right. We'll have to have a crack at changing out the OS when we do maintenance in a month or so's time. If nothing else the CPU speed boost well help.

I'll have a try with the GUI version, jackd and x.org on a spare pi, but I'll have to see. I've yet to get jackd working stably on a pi and we would struggle to use the alsa version due to our AoIP distribution.


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PostPosted: Tue May 31, 2022 12:34 pm 

Joined: Mon Apr 25, 2022 11:19 pm
Posts: 92
I didn't have much fun with jack either so ended up using alsa-loop instead. So in my set up the HifiBerry DAC ADC Pro receives an analogue line in feed, this is picked up by ST, ST then outputs into Alsa Loop. Liquidsoap receives the audio and sends it to Icecast.

Yes the GUI definitely introduces an overhead, but as things stand with the GUI, ST, Liquidsoap, Icecast all on the same box, there's no buffering issues or any kind of CPU throttling so far, but I'd like to eventually move Liquidsoap and Icecast on to a different box to relieve the CPU of load. It is working rather hard and the CPU temperature varies between 67-70c at the moment. Still within spec and I believe throttling tends to occur at 80c and above. Running 24/7 so far without any hiccups nor crashes.

I'd give it a go with GUI first with the 64-bit OS and see how it goes. Just make sure pulseaudio is configured to match the sampling rate you set on ST and on the encoder (you should be fine if you're using 44.1khz, otherwise you need to check it's at 48Khz or whatever you chose)

I'm definitely not going back to 32-bit. I've managed to reinstall everything without issue. You could create an upgraded build on a spare Raspberry Pi if you have one, and maybe swap over the SD card during the graveyard shift or perhaps when it's the holidays.

Have a look at my long thread when I started getting into all this, Minetti was super helpful with his advice and tips and did mention a trick with Jack you could use to send audio point to point between Raspberry Pis.

viewtopic.php?f=2&t=32372

You'll find it towards the end somewhere. I actually got ST to recognise Jack and got the link to work. But I had trouble selecting the jack inputs correctly on ST so had to pause it for now. You might have better luck.


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