Stereo Tool

Automatic stereo pilot on/off.

Is it possible, when the input is pure mono signal, the stereo (mpx) 19 khz pilot switch to off ?
This will help avoiding stereo noises like hiss to be present in microphones, old mono tracks etc.

Thanks.

Not needed. Every new receiver (especially car ones) measures the RF noise floor. And as i know , if noise floor is around 15 dB below RDS , which means -60 , then Stereo is automatically ON . Yes, it`s ON on screen , but in real hearing it`s OFF. When noise floor gets below "programmed one" , Stereo is really ON . Try it and you will find what i`m talking about.

And this is done exactly for the reason you mention - stereo noise when not enough signal for it.

Additionally, some receivers have difficulty in turning the stereo back on, when pilot is back (my Grundig for example). So if implemented, this would have to be option only.

With that pilot ON and OFF it would be really anoying when it switches, especially at lower level signal. That's why car radios do "blend" it's not fully ON or OFF.

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I said exactly that . In real, car radios NOT switch off the pilot . Only the demodulator part L-R is switched off ( i.e. 38Khz generator). Pilot is always ON. I saw many types of car radios and all are NOT switch Off pilot .

In fact , this discussion is not needed on ST . It`s enough that it has Switch Off checkbox and user can do it (if wants) . Auto is not needed

Going out on a limb here... I might suggest that zhta1972 could be asking if ST can determine that incoming audio is monaural and automatically switch off the pilot.

Many years ago, the FCC required that multiplex could be transmitted only when the content was really stereo. Some stations took this to an extreme, installing dual microphones in their studios. Clever disc-jockeys intentionally abused the effect by moving their heads left and right... a lot... thereby showing what wonderfully creative personalities they were.

I don't think an audio processor is necessarily the place to make this choice. For one, the system would switch the pilot off during announcer (presenter) speech, and maybe even when stereo background music might be too low in level.

In the 'States, we do tend to turn the pilot off on predominately talk-centric formats, like news or sports. I would agree that it would be confusing, and maybe even difficult to allow the audio processor to make these decisions for the station.

Better, I think, to put some effort into cleaning up the incoming content, rather than expect the processor to do it all.

The receiver makes it because of NOT to have noise ! But you want totally to smash the ST by all these things. Content watching , low level stereo background . This is insane.

Count my vote in support of auto stereo on-off. One of the large-market stations for which I have engineered uses this feature via another processor. Station is a mix of mono talk and stereo sports on a tall-tower, high-power signal located some distance from a hilly metro area -- and the auto-switch worked quite well to quiet reception noise on my 2007 Ford radio. Never heard any artifacts from the switch working -- which in this processor is accomplished by fading the pilot on and off.

Ahhhhh..... had to look that one up. Didn't know anyone was doing that commercially. Figures it would be on an Omnia. I'm not aware of any station in Washington state that uses this, and I haven't heard that it might be in the Portland area. That's 80% of my travels, so I don't know that the idea has gained any traction here.

I actually already built in support for switching stereo on and off when I updated my clipper and stereo generator/RDS encoder to be used in the Omnia.9sg, which does have this option. There are a few issues with this though, which is why I never added this feature:

1. Car radio's normally do this automatically. Meaning, as long as the L-R signal doesn't exceed the noise threshold, the car radio will just completely blend to mono. I never hear any stereo noise on my car radio, not even on talk stations, and not even if the reception gets weaker. My car is from 2012, a 2007 car as mentioned above might indeed behave differently, and cheap portable radio's definitely do.

2. I have a Philips radio that doesn't go back to stereo after switching to mono.

3. I have another Akai radio, which takes about half a second to switch to stereo when the pilot appears. Which means that when content is stereo, the first half second will be played in mono. *** -> Idea below

4. Say you have a portable radio and you tune to a station, and fine-tune it to sound good. Then if suddently it starts broadcasting in stereo it could sound horrible. If it had been stereo all along, you might have tuned it better, which would be good, or you might have searched for a different station, which would be bad. I'm not sure how big of an issue this is.

5. Not sure if this is true, but at an Omnia presentation a few weeks ago when we mentioned Auto Pilot (as it's called in the Omnia.9 and .9sg), one person said that some car radio's skip mono stations. I'm not sure if this is true - I do know that many car radio's will skip stations that don't have RDS, but since there are no mono stations here at all I would have to test it with my own transmitter (and then find multiple car radio's to test). If anyone knows more about this, please tell me!


So, I never implemented this due to these reasons. And because it didn't seem to be needed. But I just realized, reading Dr_Technical's post, that if you have a station that's broadcasting in mono - say - 95% of the time (with as exception jingles and ads), it might still be useful. The 2 news stations that we have here play at least one or two songs per half hour, plus ads, so I think they are still broadcasting stereo content about 25% of the time, and for a station like that I think the compatibility issues might be more problematic than the potential gain from doing this.


*** Ha! I just realized, the biggest issue when switching to stereo is that often the volume can be different because of phase cancellation effects. So, if I fix phase cancellation effects in the first second of stereo output, and then blend to not fixing it, it will be far less noticeable. And I already have a filter for that! (Stereo Image, with Phase set to 0%, start growing to 100% after 1 second). Hm, this might also be a nice feature to add to the Omnia.9sg!