Stereo Tool

Oh, what I wanted to see is if setting the RDS level higher would reduce the measured offset (so there still needs to be a pilot!).

Overdriving the settings can NEVER lead to a 57 kHz tone. So that cannot be it. (Does the MPX display in Stereo Tool look good and clean?)

Yes, really clean. Sharp cut at the end of the band pass filter, clean peak of the stereo pilot and clean double tops of 57k.

I've found an older measurment. ST is processing the sound, Stereo and RDS are from AEV Stargate. ST has in and out an old cheap SB.

I'm gonna post some images from my pira for you.
I use ESI Juli@ soundcard to a home build transmitter. When i don't calibrate the 57 kHz i have phase +8/9 degrees. So now i put the 57 khz phase slider a bit higher and with no sound it's around 0 degrees. When i play music it changes a bit, but that's probably because of the accuracy of the pira.

No input signal to transmitter:


No input signal to transmitter and double base on:


RDS and Pilot calibrated (the phase changes a bit between 0 and 1 because of the accuracy of the pira):


RDS and Pilot calibrated double base on:


Output when playing music:


Output when playing music double base on:


Try the phase measurement with no sound and maybe better signal to the pira and check if the value doesn't move.

Eldoradofm: Your signal looks MUCH cleaner - and 8 degrees sounds much more reasonable (although it's still more than I had hoped the Juli@ would have). At least this seems to confirm that Stereo Tool's RDS generation is correct.

EldoradoFM: You probably need to alter the other sliders a bit too to get the best possible signal. I think I should order a Pira myself to play with it a bit - that would make it much easier for me to see how the calibration can be done based on the information that it provides. More specifically, it´s not very clear if you need to move the 57 kHz slider (and probably the sliders around it as well), or the 19 kHz slider. Or even all the sliders (tilt).

@eldoradofm : Thanks for the images. I'm already comparing my station to others running Omnia3 and Omnia6 but yours are really helpful since you run ST. I really like the end of your band pass filter, it's really cutting everything above 16Khz.
I'll try the same test and will post back more images.

Btw, are you moving the slider of 57KHz at the first step of FM calibration (MPX method) or at the third one?

@hvz : Maybe you should. The Pira.cz guy just released a new version, the Pira175 which is also USB capable and can be run on 2 AA batteries.

Let's say that my TX needs some calibration. Let's say that some sliders need adjustment. Should the "Enable FM Calibration" box be ALWAYS ticked when in operation or not? I suppose yes, but I want to make sure. Hans, I think that the explanation text you've written on the sliders popup window, may need to be in more detail.

@Hans, i think my transmitter is not totally "frequency flat" so that's probably why it's more then you hoped.
I'm soon gonna buy a Marian Trace Alpha and i'm looking for a better transmitter. Leif told me that he's using the 1 WATT BW PLL+ transmitter and the only calibration for that one is the input level when you use a marian trace alpha card. So it will probably be that one.
Also i don't trust the levels that the pira analyzer shows me for the pilot and rds deviation, but it's a nice indicator.

Yes for proper calibration i have to set more sliders because i now have tilt.
But i'm waiting for an easier solution where i can do it with only 1 slider. And it would also help if i can see the values i've set in degrees under the phase adjustment meters.

For proper tilt correction MPX tool is a nice tool to use and probably way more accurate then the pira analyzer. But then again that has to be calibrated so i first must have a good known soundcard for MPX and a good transmitter. Then i can calibrate MPX tool and then i can do proper adjustments for different soundcards and transmitter combinations.

@Lef
For this RDS phase calibration i only used the 57 kHz slider for the phase at the bottom on the right.

Yes the Enable FM Calibration box must always be ticked when you want to use the calibrated settings.

I've done the same tests with eldoradofm.

This is the result with no input in ST.



This is after I've calibrated, no input in ST. To achieve that, I had to set the 19KHz slider to +1/4 (measuring 0 at the bottom, or -50%) and the 57KHz slider to 0. Pilot volume to 7% and RDS volume to 4% (aren't those related to the audio playing?!?)



Now I enable the input on the ST. The FM calibration tickbox is on, at the previous calibrated values. In this case there is a drop on the stereo pilot, RDS goes up and I am getting a positive phase diff.!!

]

Finally, I disable RDS and there is still something there. FM calibration is still enabled.


So I suppose that something in the chain is picking up noise on 57khz. It amplifies the original RDS signal that ST produces. The noise of course is not in any phase relation to the pilot, it's just noise, and it's causing a phase difference between the stereo pilot and the sum/total of the 57khz signals. So it's a mess.

I've just seen your new screenshots. I see you have a lot of noise with no input signal, so something must be wrong there. You can try disconnecting things and try to find what's causing it. I find it very strange that the pilot drops when you add music. Could it perhaps be that the input from the soundcard leaks to the output? Or maybe some grounding problem.

After spending many times calibrating and messing with all sliders on FM cal., I've found a new thing. If a play a lot with post and pre amp, I can achive a phase diff of +15 to +5 deg (FM cal on). That happens when I lower post amp to about -2db (was originally 0db) and pre amp is at +23db!
Don't know what happens here, but I'm just getting a fair phase diff. Deviation on most Top40 songs is going from 50khz to 70khz. Anyway, I think I'm getting closer.

When songs fade out and there a small silence between, I think i can hear a rattling sound coming from RDS. Am I right?

You should NOT be able to hear that! It's at 57 kHz! Do you hear it when you listen to the sound card output, and/or on an FM receiver?

Could you please try the stand alone version, set at 192 kHz? I'm starting to think that something is converting the audio to a different sample rate than the one Stereo Tool is sending, every RDS/stereo capable sound card supports 192 kHz so that might be an interesting test.