Stereo Tool

Hi all,

We have recently installed a new TX and ST into a new TX site for our community station. I'm not an engineer and I only configured ST on a PC that the engineer brought up there, using a UMC-202HD sound card (TS to BNC coming out from the back L channel). However, the engineer showed me this and said we're way too hot on the RDS side and it also looks to me like we're not as hot as we can be on the L and R either - which I can tell is affecting our loudness compared to other stations? I was asked to raise the volume of the sound card's output because it was coming into the TX way too weak so I increased the MPX level to the max, which may not be the way to go? There would also be an option of using both the L + R outs into the BNC to increase the strength? The headphone jack is another option, as it's hotter, but I'm a PC sound guy and don't know how that translates into a clean MPX signal. I did try to apply some tilt correction while he was up there (and I remoted into the PC from home) but it didn't seem to help and changing the RDS Injection level (4.5%) didn't either.

Below is a photo the engineer sent me. The transmitter is: https://www.sielco.org/en/product/exc300gx-16. We did not get any of the addon boards, such as the Stereo Coder or RDS, as we're using ST for that. Also, here is a slice of our preset containing the I/O and FM Signal/RDS settings: https://www.lccr.ie/LCCR_Broadcast_Settings.sts. It would be massively appreciated if anyone is willing to share any insight into the problem. The engineer doesn't use ST and isn't familiar with these sorts of custom, improvised MPX solutions, which is why I'm asking here. Ultimately the goal is the get the RDS in spec and get the dB loudness up closer to that zero - which I guess is where it needs to be to be considered "loud" enough to stand as tall beside other stations?



And here's our brief WhatsApp conversation that occurred while he was up there doing the install. We talked mostly on the phone so this is all I have that I can show you.

Hi,

load this preset, beheringer umc202HD linearization, 30-70.000 hz @75 khz, +/- 1khz.

https://www.mediafire.com/file/u40lwp02 ... r.sts/file

P.S. OUTPUT LEVEL UMC202HD @MAX

Best regars
Luca

Hi Luca.

Thank you for sharing your preset; it's seriously appreciated. We only broadcast on FM on Saturdays and Sundays so I've loaded your Broadcast and I/O settings and changed what's needed but kept all your other stuff including the Tilt Correction (of which yours was more "corrected" than my guesstimate), etc. We don't use the Composite Clipper - maybe that's something we should invest in - so I've knocked that off as well, and also changed the RDS text settings and PI code back to our own. We'll have to run some tests during the week.





One thing I'm curious about are the ST Input and FM Output settings. Our feed is coming in from a high-quality AAC-LC stream, so I've tied that to a virtual cable on the Input. I saw your Input was set to the UMC's ASIO but only the L channel was set - so you're coming into ST with a mono feed, or is this in error? But on the Output, both L and R were set. And, since we're only using the L output on the UMC (TS to BNC), what do you think would be best here - turning off the R in ST or setting it to use the UMC's 1 L as well? Are you using both of the UMC's output jacks to go to the TX's BNC MPX input?

Hi,

you're right, I had mistakenly inserted only channel 1 in the input, of course it is correct to use both channels (L & R), as regards the output I recommend that you also activate channel 1 (L) and channel 2 (R) in that case for a second auxiliary MPX output, of course only one output from the sound card or L or R, towards the transmitter will be enough.

Best
luca

Thanks again, Luca. Out of curiosity, did you notice that you needed to turn the gain up on the TX by a lot when using the UMC202HD? I've used this on two transmitters and the first one I configured myself, and I had to really turn it up compared to the when the discrete Stereo Coder was connected, and on the second TX, the one the engineer installed, he was asking me for more loudness. Is that just because of the characteristic of this soundcard, that its output just isn't that hot? I had toyed with the idea of setting both the L and R on the FM Output ASIO settings to use the 1 L, but I have no idea if that would help or make it worse (or ruin the MPX signal completely).

Hi,

I have never tried it in direct input on a fm tx (it shouldn't change anything) I usually use it at home for classic listening use, my new laptop has a terrible sound card, I had done some tests just bought towards a 2ghz tx, a sielco exc19 ..... but tomorrow I can try it in the lab.
I forgot to tell you one thing, the level of the output potentiometer to have 75 khz, must be at maximum based on the preset I shared.
anyway, as said before, tomorrow I will do some tests in the lab and I will tell you.

ps. you should not touch the gain of the tx (with that preset the tx at 0db), use the bessell null test in stereo tool...

audio i/o
Fm out
more fm output option
13587 bessel null
and you must have 75khz on the tx

if with output at maximum and preset that I shared you do not have 75 khz in on the tx there is some other problem.
the cable rg58 or rg59, bnc -> jack 6.3 mono?

best
luca

Luca, you're very kind to have offered to help like this. I'm learning as I go...

I'm making arrangements to get up there tomorrow evening after work to do what's needed, including the Bessel Null test tone calibration, as you described. The cable is a 6.3 TS jack (mono) to BNC coming out from the 1 L output at the back of the UMC202HD. Also, in Windows the output volume is set to 100.

Hopefully all will be good with the test, and while I don't have an analyzer, I'll have to make do with the TX's deviation meter to ensure 75kHz. I imported your preset, merging it with my processing, and resetting applicable values back to ours for the RDS, etc.

When you say the gain at 0dB on the TX, is it the "Nom. Input" measured in dBm controlled by the interface? On the last TX we had, it was adjusted via a jack screw/pot at the back. In this case, the manual says the default is +6dBm, which I'm sure I can adjust to 0: https://www.sielco.org/files/webpages/0 ... GX_ENG.pdf.

EDIT: With the Composite Clipper not being used, would I need to make any adjustments anywhere else in the preset, or even the TX or will it just be (naturally) a few dB lower with everything else remaining as is? And one more stupid question: if I were to upgrade to FM Professional to get the Composite Clipper and apply your settings for that, would we need to recalibrate to ensure 75kHz - which would likely depend on any changes made to compensate for not using the Composite Clipper...?

Hi,

all sielco devices (tx, rx and tx fm) come out of the factory at +6 dbm, so you will have to adjust the mpx input to 0dbm, I think that is the problem...so follow the instructions in the manual at point (18)

In the previous message, I specified the output potentiometer of the umc 202hd, not the audio output in windows (using asio you do not go through the windows volume) screenshoot in the link
so turn the output potentiometer of the sound card to maximum, at the output you will have 2.2 Vpp i.e. 75khz of modulation.

https://www.mediafire.com/file/52a5g6rm ... D.jpg/file

I don't know why I can't insert images in this post.

as for the clipper, certainly if you update the license you will have a few more db of volume, I recommend it, you will not have to make any changes if you activate it.

P.S. be careful... do not overdo it, clipping is a "drug"

Best
Luca