Stereo Tool

Hi,

In my case i have -24° phase difference , it is not good

How to calibrate this ?
Thanks
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PIRA75 Documentation :

Pilot-to-RDS phase difference
The 57 kHz for RDS subcarrier was chosen for being the third harmonic of the pilot tone for FM stereo, so it would
not cause interference or intermodulation with it. The amount by which RDS subcarrier and third harmonic of pilot
tone are out of step with each other can be expressed in degrees from 0° to 360°. Since the RDS signal is based on
its carrier phase alternating, the full angle reduces to straight angle and we can equate 90 degrees = -90 degrees.
During stereo broadcasts the RDS subcarrier will be locked either in phase (0 degrees)
or in quadrature (90 or -90 degrees) to the third harmonic of the pilot-tone. The
tolerance on this phase angle is ±10 degrees.

That's a lot! That also might mean that the new mechanism to calibrate phase differences with one slider (to compensate for capacitor effects) would not work at all in your case. Which sound card do you have??? And how long are your cables to the transmitter? (Yes, that can make a HUGE difference).

Ok, about calibrating. This huge difference must mean that there are more problems at other frequencies as well. So it doesn't suffice to just calibrate this one frequency (57 kHz) in the "FM Calibration" window, you'll have to calibrate ALL the frequencies.

Have you checked this window already? You can find it on the button on the bottom right of the FM settings window.

Merde alors

Something is not correct then.
If you have that much phase shift then the stereo seperation must also be very very bad.

I prefer to first know what this is causing this than to try to change it with software, meaning the sliders.

Now to find out how can be a bit more tricky.
It can be that the transmittor input which has a capacitor to ground. A wrong designed audio deviation circuit at the oscillator can also be the case. ... so many things.

Can you give us the complete setup like which soundcard, cable and how many meters, which transmittor?

It's ok

I put the slider 19k up little and my phase diference is between -1° and 1°

that's good

ST is connected by Xonar Essence STX sound card in a STL Link transmetter 8.5 Ghz Analog, at the broadcast site we have the receiver of STL Link connected to RVR TEX 502 LCD FM.

Thanks

It may be, but your audio is probably NOT good at all, with big spikes and bad stereo separation. It doesn't suffice to adjust just one slider till the phase difference is gone, because if there are such big differences you need to either (preferably!) find the cause and fix it, or adjust ALL the sliders to get a good signal.

Do you have any measurement equipment, such as a Pira or something professional?

If not, you can just use an FM receiver to adjust everything - it may be less precise though.

As Hans says, it does not take away the cause which is a bad thing.

I suspect the STL causing phase shifts but you will only know that by trying.

A simple thing to try: Only send like 1 channel (left or right) to ST. My suspicion is that the channel seperation is not good at all if you listen via a tuner on air.


Maybe there are other options in the setup which should be changed to get a better result.
The more analogue equipment is placed from ST to the transmittor the worse the signal will get.
In equipment I mean cables and devices.

Due to the full mpx signal there are a numbers of factors which should be as close to perfect as possible. Flatness of the audio has to be perfect from 20Hz to lets say 60KHz and this without any phase shifting.
Each single device that you use from your soundcard to the transmittor will change (always worse) those 2 things. The result will be bad stereo seperation, overshooting audio, etc etc

I don't know if it is possible to have the ST computer next to the transmittor but that is what I would want to do.