I've noticed a few stations that their Stereo pilot turns on and off automatically depending on if their programming is in Mono or Stereo...anybody know how this is done? I personally think it's a genius idea.
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Auto Stereo Pilot
- Thread starter fmradioguy
- Start date
Some stations have been doing that since at least the 1970s. The stereo exciter detects if there is anything in the stereo difference component (left minus right), and if there is no stereo audio content for several minutes (to avoid constantly fluctuating in and out of stereo mode), it drops the stereo subcarrier and pilot tone. As soon as stereo programming returns, it kicks back on the subcarrier and pilot.
Or, the station can program their exciter to turn on and off the stereo according to their programming schedule. Many NPR stations do this -- they only turn on the stereo during programs with musical content.
Or, the station can program their exciter to turn on and off the stereo according to their programming schedule. Many NPR stations do this -- they only turn on the stereo during programs with musical content.
Genius? Hardly. It used to be a rule. Nobody ever got dinged for not following the rule, but it was.
Back in the day of that little red 'stereo' light, programmers never wanted to have the station run mono, because they were concerned that people could be tuning across the dial wouldn't stop on a station where the little red light didn't come on. (red light means stop) Some stations tried to have it both ways, by inserting a 19kHz tone into mono audio to turn the stereo light on.
There was a bit of controversy at the time as to whether doing so was legal or not.
Orban sold a lot of stereo synthesizers to radio stations who wanted to be stereo 24/7, by automatically adding a fake stereo effect to mono programming. Even just adding a bit of stereo reverb would probably be good enough to count as "broadcasting in stereo".
Stereo indicators aren't even in people's cars anymore... My car radio stops the scan every time on our local 100kW Sports/Talker which is in Mono... If there's no stereo content, why broadcast in Stereo constantly? It doesn't make sense. Use Stereo when needed, broadcast in Mono when programming isn't Stereo to get your signal further...
The absolutely last thing a station should do is constantly switch between stereo and mono. That would make for an inconsistent listening experience.
Many sales departments are against being mono if the commercials are produced in stereo, which if they have music, usually are. No AE, GM, or GSM want clients thinking their station is technically inferior, when the competition airs those same spots in stereo.
Turning the stereo pilot off does not make your signal go further. It's an old wives tale. Nearly all FM receivers are designed to "blend" the left and right channels when the received signal strength goes down .... switching completely to mono when the signal is very weak.
More recent FM receivers have the stereo blending feature, while older ones do not. Back in the day turning off the stereo pilot resulted in a lower noise floor on marginal signals. A number of older receivers also had an internal adjustment for stereo capture threshold, where you could set the signal level for switching from mono to stereo.
Stereo blending is a double-edged sword for in-car reception. While the noise floor is kept more or less consistent, the constant changes in the stereo "soundstage" can be an annoyance. Music in mono or heavily blended has a duller sound than full stereo separation, and rapid changes on a marginal signal can result in a poor listening experience. Personally I find a varying noise floor less distracting than rapid changes in the soundstage.
Of course one thing missing from most modern FM receivers is the "mono" button which allowed users to manually kill stereo reception. And I recall some receivers where the stereo blending feature was a user option.
Guess I didn't realize this. When I was taught how to set up the stereo generator on a processor, I was told the higher the ST pilot injection level is, the more of your signal it takes up. For example, 8% ST injection is 8% of your signal taken up by the Stereo pilot...I guess I was taught wrong. 🤷‍♂️
It doesn't change the signal level. It reduces the available modulation slightly.
Thanks for clarifying.
I assume this is the same with RDS injection. Rather than signal space being taken up, it just decreases modulation available to use slightly...
That is correct.
That's why Kelly said "back in the day". I definitely used the brightness of the stereo indicator to tell me when I had centered up on a frequency on the boom box my parents had in the house as a kid.
But once we got a radio with a CD player and digital tuning, that was no longer necessary!
Many modern car radios blend FM to mono so aggressively that you practically need to be parked under the tower to hear the signal in stereo -- and they also severely roll off the high end to mask static. It's the transition from analog to HD which is far more jarring, because the audio suddenly goes from muffled mono to crisp (but artifact-laden) stereo, or vice-versa.
That's the real double-edged sword: do you take advantage of HD's lack of a pre-emphasis curve to make the high end brighter and cleaner than analog, or do you match the EQ between analog and digital to make the transition less annoying?
That's the real double-edged sword: do you take advantage of HD's lack of a pre-emphasis curve to make the high end brighter and cleaner than analog, or do you match the EQ between analog and digital to make the transition less annoying?
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