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Over modulating
- Thread starter 192khz
- Start date
Safe from what? In the USA, it is not legal.
In the more distant past, radios did not have the bandwidth to accommodate that degree of excess, and would sound awful with an overmodulated situatioin. Newer radios that have digital signal processing, as pointed out by Kelly, are even worse.
Where high modulation is tolerated is primarily in nations with lax enforcement of modulation limits.
Not really if you have a good audio chain starting with some form of AGC and then a limiter with absolute peak limiting. With today's gear you can generate what looks like a square wave on the scope without exceeding the peak setting.
Ive just found using mpxtool stations near me are over modulating at 130% it seems.
Off the shelf spectral software developed in China, is often not accurate enough to make that determination.
To be even reasonably accurate, the software would need to be calibrated to the multiplex output level of the tuner. Without a reference FM signal, calibration is not possible.
Not to mention that if you are some distance from the transmitter site of the station in question, multipath can easily add several percent to the modulation "measurement".
You've just discovered what engineers in competitive markets have known for decades. Field measurement of FM modulation is not simple, requires a monitor that is carefully calibrated, a wide-band front end, and an antenna with location that provides a multipath free RF signal. There have been frequency-agile broadcast modulation monitors over the years that solve the first two problems, but then are still faced with the antenna/reception problem. You have all three to solve before any conclusions can be drawn.
And you can also use a little logic. Even if an FM station doesn't have an actual modulation monitor, their exciters have a modulation meter that is pretty accurate. They do know what their peak mod levels are, and nobody intentionally "speeds" to 130%. 73.1570 allows for more than 100% if SCAs are included, but the total can never exceed 110%. If you see more than one station doing 130%, consider the calibration problem must be on your side.
192khz earlier did you tell us you are a young person? Are you in a small town or city where a radio station might show you around and maybe give you an opportunity to experience the environment? If you are interested in the technical side of broadcasting, getting to know a local broadcaster can be helpful. Then you can come on here and ask why a local station does something. Then we could discuss the intersection of people, business, audience, markets, etc. which may in turn answer your modulation question.
I notice others here are taking time to provide accurate and correct answers to your questions. They don't have to do that.
I notice others here are taking time to provide accurate and correct answers to your questions. They don't have to do that.
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Yes, Yes I am. I'm in a suburban area so plenty options for exploring radio. The only thing is how? I've tried contacting many PDs and no response.
Seems as the 130% was actually some multipath or distortion in the signal. It averages about 115-120%
Yep! Re calibrated and it seems as the peaks are about 120% max.
Re calibrated and I'm reading about 115% max.
Recalibrated and I'm reading 115% max
Chances are, for the same reason, even that is higher than what it would measure with proper equipment. The fact you can change 'calibration' and see a change of 15%, is a clear indicator the application is for fun, not for passing judgement.
H
Harvey_Dogg
Guest
In my area there are several FM stations that are compressed into distortion. You might think your amplifier is blown up.
But they are not overmodulating.
But they are not overmodulating.
And that's so destructive to Time Spent Listening. Why some PD's or station owners still live in the 70's, is beyond me.
At co-located sites I see a number of stations modulating 125% or more ON THEIR MOD MONITORS. The pressure from PDs and GMs to be louder than the competition hasn't changed in the 50+ years I have been in the biz. When you try to explain the downside of that amount of modulation it's like trying to teak a pig to dance. (Waste of your time and tends to anoy the pig.)
Had one of those rare PD's at one of my stations who allowed me to prove my theory, at the time and today, that excessive processing reduces TSL. He allowed me to back the processing off to the point where there was actual dynamic range and very flat equalization. As expected, in-demo TSL went up (as I recall) about 22% in the first full book of the test.
Overmodulation also increases the potential for multipath distortion.
Well, yes and no. From a pure physics angle (pardon the pun); multipath are signals reflected off man-made or natural surfaces which arrive at a receiver in different times than the primary signal. Depending on the timing/phase, some of the reflections can cancel the primary signal out, effetively causing the receiver to appear as a loss of signal. ( I know you already know that Frank, but for the benefit of others reading)
I believe what you're referring to Frank, are the effects of Intermodulation Distortion (IMD), where excessive harmonics from the L+R bleed into the L-R, causing to a listener what sounds like multipath, or phase cancellation between the two subcarriers. Stations that have older composite stereo generators suffer from this more when they choose to run excessive clipping in their audio processing. Something similar can occur with older FM exciters being fed by even modern one-box audio processors with integrated stereo generators. Composite filters in the exciter can ring with dense audio, causing excessive harmonics in the modulator section of the exciter.
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