Stereo Tool

Hi all,

I'm a long-time Stereo Tool user - for online broadcasts - but somehow I never managed to register an account on the forums!

I'd appreciate any help you can offer on this matter, so let me explain the predicament:

I've been using Stereo Tool since 2014 at a community radio station. We broadcast 24/7 online and we're licensed to broadcast on FM for 100 days per calendar year, so we do about 48-50 weeks on Saturdays and Sundays. Our license permits us to use a local university's student station for our FM broadcast, and the university has been happily on board to let us do that all these years. At some point we'll go out on our own but in the meantime the issue with this setup is that we don't have much control on how things are done on the tx site, so we've basically been sending our processed audio to their studios and a codec handles the streaming to the tx site.

It may go without saying that the sound over FM has always been...well...awful. They don't have much in the way of audio processing and the dynamics of our processed audio are completely destroyed. I believe their tx chain is Codec > Stereo Encoder > RDS > Transmitter (some version of the TX300 - definitely an older one). We've put up with it for years, but I have always wanted ST on-site and I'm going to make a case for that. But first, it has to be tested, and I'm a "n00b" when it comes to transmission/transmitters.

I have a Dell Optiplex 3040 Micro with Ubuntu installed. Stereo Tool (ALSA) seems to be running stable with a Behringer UMC202HD @ 192KHz. So the question is, on the TX300, is it possible using the analog XLR inputs to send in the FM Pilot, Stereo, RDS etc. while disabling the internal processing/encoding? And would I need to disable the tx's Pre-Emphasis, or keep it at 50μs? It's the big unknown for us right now. I know there are MPX inputs and digital inputs, but the UMC202HD is analog, like most consumer sound cards, and I'm hoping someone here will know if the analog XLR ins on the TX300 will do anything with the full MPX out from ST. The overall aim is to unplug the existing Stereo Encoder and RDS and just use ST, but also, until I get up there, I'm not even sure how those units are connected up to the TX300 and what options are enabled and disabled.

So just on the basis of using the analog ins, is it possible to knock off the internal features and for it to work with the ST MPX?

Thank you for any assistance/insight you can provide.

You just need pure mpx input on transmitter. Also be sure to fully disable i lnternal stereo coder (if any) and depending on transmitter, switch input to MPX.
You will also need some measurement tool to adjust it to max 75kHz.

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Hi Bojcha,

Thanks for replying. I watched Hans' video on setting up an FM station in 5 minutes many times, hoping to one day do it myself! So the plan is to keep the deviation @ 75kHz so long as I get the other bits and pieces worked out beforehand.

I believe the MPX inputs are F-connectors. See the rear of the TX300 V3:
http://audionica.eu/wp-content/uploads/ ... XV3-2U.jpg

Then there are the XLR analog inputs, which is why I was hoping anyone with experience using any version of this transmitter could comment on their ability to take in the ST MPX output and correctly transmit the pilot, stereo, and RDS.

That is Classic BNC connector. Idk why there is 2 of them but you need to use 1 MPX IN. Probably there is switch to choose what MPX IN is in use, or maybe it can be used for backup, check manual. Also don't couple both channels from soundcard use one of them.

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Thanks again, Bojcha.

I've read sections of the manual already but I just wasn't 100% sure.

So are you saying that I should cable the UMC202HD's left out (leaving the right out empty) with a BNC on the other end, like this cable here?:
https://www.amazon.com/Alvins-Cables-Te ... B079PZXVRZ
(I know this cable has a 3.5mm TRS; I'm currently looking for a 6.3mm, but will use an adapter otherwise)

Hopefully I'm not misunderstanding. I'm going up there next week, so this is why I needed to post here.

Okay, so I re-watched Hans' video and I can't believe I missed this because I was so laser-focused on the XLR connectors at the back of the tx, but I see he used a phono to BNC adapter.

So I could get one of those easily. I also have one of these cables that I ordered last week for another reason:
https://www.amazon.co.uk/gp/product/B01CT1XHMU

So I could just plug the left channel TS in on the UMC202HD L out and use the phono on the other end to go into the BNC adapter and into MPX In 1 on the transmitter?

Yes, but try to avoid adapters and try to find or make proper cable. 6.3trs to bnc.
https://www.ebay.com/itm/392181198215

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I hear you - I hate using adapters, especially the 3.5mm -> 6.3mm or the reverse, as quality control issues are common.

Your suggestion on eBay looks perfect but it's in China, so shipping will not be speedy. In the meantime at least, how about using what I have on-hand - the TS to Phono cable I linked above with a Phono -> BNC Adapter? As long it would do the trick for next week (which is just for testing). Ideally then I can wait to get the TS -> BNC.

Thank you again. You have a wealth of info on this topic!

Who'd have thunk it - Amazon to the rescue! I couldn't find anything on eBay within the EU or the UK - everything was coming from China - but I've now ordered this on Amazon with an estimated delivery date (to Ireland) of early next week:
https://www.amazon.co.uk/gp/product/B08H1KW6ST

Hope this helps anyone else in need!

Just to update you all on this:

Thanks Bojcha. We were successful in getting it to work but even with the volume in Windows an Stereo Tool set as high as possible, coming out from the back L or R jack sockets of the Behringer UMC202HD, using a straight TS to BNC or a TS to RCA Photo (with a Phono to BNC adapter), the max deviation was 50kHz (with an average of somewhere in the 40s), so it was very under-modulated, to the point where one of our car radios wouldn't even lock to the frequency for more than a few seconds and tried to seek. The best solution for the moment seemed to be to use the UMC's headphone out at exactly 50% volume (knob at 12 o'clock) with the MPX volume in Stereo Tool at ~0.70dB. By the way, I dumped the Ubuntu 20.04 idea and just installed Windows 10 21H1.

A Focusrite Scarlett 2i2 2nd Gen was also tested with the same results as the UMC coming out from the rear L or R outputs.

If anyone has any experience with either of these soundcards going to a transmitter, did you use the headphone jack also, or did you manage to get it correctly modulating coming out from one of the rear outs?