Mono for Talk on FM

[carolinaradio]

Talk also sounds better on mono in FM because without the stereo, you can (for lack of better engineering terminology) crank the audio up without it over-modulating/clipping. A lot of FM talkers in mono are louder than even the music stations and certainly the stereo talkers.

Has anyone here experienced a stereo that won't stop on mono? Tried yet another radio, a circa 2004 GM radio and it will stop on a mono station if its strong enough (or it may spot the RDS).

 

[rrsounds]

Talk also sounds better on mono in FM because without the stereo, you can (for lack of better engineering terminology) crank the audio up without it over-modulating/clipping. A lot of FM talkers in mono are louder than even the music stations and certainly the stereo talkers.
<snip>

When monophonic audio is fed to a stereo generator, no signal in the 38 kHz subcarrier range will be present at the generator's output. The subcarrier only 'comes alive' in the presence of stereo audio.

In other words, the ONLY difference between transmitting strictly 'mono' (no stereo generator) and mono programming on a stereo FM radio station, is the presence of the 19kHz pilot in the signal from the active stereo generator, making program audio very slightly lower in modulation (<10%) to make room for the pilot. But otherwise, the signals are IDENTICAL.

The truly dramatic advantage to turning off the pilot during mono programming is purely receiver-side, and this advantage really only applies to stereo receivers: with the pilot on, a stereo receiver may decode whatever noise lies in the subcarrier region, and add it into the detected left and right outputs. This noise can be considerable, and is all the more noticeable with mono programming because the noise occurs spatially in the listening environment where there is no other audio to mask it (randomly to the far left and right).

Other than the less than 1 dB loudness advantage of having no pilot, a mono receiver will detect virtually NO difference between a mono transmitted signal and a mono program on a stereo FM station.

FWIW, to the best of my knowledge there is no processor presently available that allows for monophonic transmission of audio bandwidth much greater than 15kHz, but this is a moot point, since any given modern receiver can be expected to have similar bandwidth limitations. Practically speaking, wider bandwidth would be wasted on speech, anyway.

There was talk a while back about modulating the level of the pilot to dynamically mirror the amount of L-R (IOW, no pilot with mono input; full pilot with stereo input audio). But I never heard much more than some vague talk. Maybe someone can tell me why this is a bad idea.

Kind Regards,
David

 

[rfry]

FWIW, to the best of my knowledge there is no processor presently available that allows for monophonic transmission of audio bandwidth much greater than 15kHz, but this is a moot point, since any given modern receiver can be expected to have similar bandwidth limitations.

This is interesting, as it relates to the claims made by some that the complete, digitally implemented air chain, including the stereo FM audio processor should use sampling rates that can support stereo audio response to an upper limit of about 22 kHz -- regardless of whether typical FM receivers and home sound systems can usefully detect and reproduce audio much above 15 kHz, that their typical listeners can even hear such, and that those listeners would even notice if frequencies >15 kHz were not present

//

 

[RadeoEngineer]

FWIW, to the best of my knowledge there is no processor presently available that allows for monophonic transmission of audio bandwidth much greater than 15kHz, but this is a moot point, since any given modern receiver can be expected to have similar bandwidth limitations.

This is interesting, as it relates to the claims made by some that the complete, digitally implemented air chain, including the stereo FM audio processor should use sampling rates that can support stereo audio response to an upper limit of about 22 kHz -- regardless of whether typical FM receivers and home sound systems can usefully detect and reproduce audio much above 15 kHz, that their typical listeners can even hear such, and that those listeners would even notice if frequencies >15 kHz were not present

//

This makes no sense in the analog world, as you can't transmit it. If this is a reference to HD, I still have doubts. Anyway, who can hear 22 kHz besides that barking dog next door?

 

[fm-engineer]

FWIW, to the best of my knowledge there is no processor presently available that allows for monophonic transmission of audio bandwidth much greater than 15kHz, but this is a moot point, since any given modern receiver can be expected to have similar bandwidth limitations.

This is interesting, as it relates to the claims made by some that the complete, digitally implemented air chain, including the stereo FM audio processor should use sampling rates that can support stereo audio response to an upper limit of about 22 kHz -- regardless of whether typical FM receivers and home sound systems can usefully detect and reproduce audio much above 15 kHz, that their typical listeners can even hear such, and that those listeners would even notice if frequencies >15 kHz were not present

//

I believe it was more about the shape of DSP filters such as the 15kHz low pass than anything else. When that debate was a hot topic (Harris Digit) one camp was arguing 32kHz, the other 48kHz. One processor sounded like breaking glass, the other was getting close to sounding analog. Today, DSP no longer sounds like that, but even Orban has gotten away from 32kHz BSR in their 8500 flagship. As we move forward, expect to see standard resolutions of 96 kHz and above. IIRC, 96 kHz @ ???kbs approaches true linear audio. In similar fashion, 15 megapixels = 400 speed 35 mm film.

 

[littlejohn]

Yeh. And on big blowuops, Tri - X looks scurvy compared to Pan x at what - 32 ASA or some such. But much better resolution.

 

[gtomas]

I believe it was more about the shape of DSP filters such as the 15kHz low pass than anything else. When that debate was a hot topic (Harris Digit) one camp was arguing 32kHz, the other 48kHz. One processor sounded like breaking glass, the other was getting close to sounding analog. Today, DSP no longer sounds like that, but even Orban has gotten away from 32kHz BSR in their 8500 flagship.

I believe they did it more for marketing reasons, than the real need. Competition pounded on their 20k HD path response in contrast to Orban's 16k (except for Orban PC-1100 which was always 20k) so they needed to bring that up, for comparison purposes. But this is all moot, as all digital radio broadcast systems that are in use today around the world, either can't reproduce 20k or noticeably benefit from reduced input audio bandwidth (at least 16k). As far as streaming goes, you need to have a very high bitrate (>160 kbps) and quality codec such as AAC to have full 20k response.


Regards,
Goran Tomas

 

[rfry]

As we move forward, expect to see standard resolutions of 96 kHz and above. IIRC, 96 kHz @ ???kbs approaches true linear audio.

Maybe so.

Such resolutions might be useful for recording/production/post-production facilities.

But not addressing this poster specifically, what is the point in transmitting, either by analog or digital means, such audio bandwidths as cannot be reproduced by the receiving systems used by most radio listeners -- and/or even audible to those listeners, if such extended audio bandwidths were present in their listening environment?

//

 

[Tom Wells]

I can still hear the 19khz pilot. I agree that the mono advantage is all on the receiver end.
If the radio has no mono-stereo switch, (as most modern radios don't) then mono transmission will definitely help most users for talk.

I have collected and maintained and used ONLY radios (AM included) that do not have lopped-off high ends.

But I'd need an A/B headphone comparison to know if the frequencies above 15 k were missing.
I'm happy with "relatively flat to 15khz".

There are times when I'm making a recording and lop everything off above x, but only if the result is a net gain.

 

[radiorob2.0]

I can still hear the 19khz pilot.

Wow, I salute you. Obviously you haven't blasted your eardrums with those loud, screamin' guitars.

 

[fm-engineer]

Maybe Frank will chime in; but again I think it was the more gradual shape of the 15 kHz LPF. The early steep DSP filters did not sound very good. So the audio up to 15 kHz sounded better with a more gradual stopband, but if you had anything above the Nyquist using 32 kHz BSR, then overshoots would occur. This is why a Harris Digit exciter overshoots with an Omnia processor, and now will with the Orban 8500. Everyone has gotten away from 32 kHz except Harris, and they never implemented a way to upgrade the Digit exciters. There was an aftermarket IC chip Harris offered called the wideband input. It really did nothing to help the problem. Again, this is a very old argument and discussion. Harris is the only company to still use 32kHz with the Digit. All other digital exciters use a higher BSR.

As we move forward, expect to see standard resolutions of 96 kHz and above. IIRC, 96 kHz @ ???kbs approaches true linear audio.

Maybe so.

Such resolutions might be useful for recording/production/post-production facilities.

But not addressing this poster specifically, what is the point in transmitting, either by analog or digital means, such audio bandwidths as cannot be reproduced by the receiving systems used by most radio listeners -- and/or even audible to those listeners, if such extended audio bandwidths were present in their listening environment?

//

 

[rrsounds]

I can still hear the 19khz pilot.

Wow, I salute you. Obviously you haven't blasted your eardrums with those loud, screamin' guitars.

Especially when the pilot is not only higher in frequency, but 20 dB lower in volume (before de-emphasis!) than the broad swath of what is typically extremely dense high-frequency material only a few kHz away. And most receivers have a notch on the pilot too, along with de-emphasis and a low-pass filter, so, kudos, I guess!

Kind Regards,
David

 

[Tom Wells]

I can still hear the 19khz pilot.

Wow, I salute you. Obviously you haven't blasted your eardrums with those loud, screamin' guitars.

Especially when the pilot is not only higher in frequency, but 20 dB lower in volume (before de-emphasis!) than the broad swath of what is typically extremely dense high-frequency material only a few kHz away. And most receivers have a notch on the pilot too, along with de-emphasis and a low-pass filter, so, kudos, I guess!

Kind Regards,
David

This is not on newer radios, which used to make me think my hearing was starting to go.
On old radios, it's still loud as ever. TV sweep oscillator/outputs used to drive me nutso.
I built a notch filter set in 1982 for 60hz, 14,758 and 19,000 and got a lot of use from them.

 

[HowardMBurgers]

If you're that worked up about turning on the stereo light (or the little "ST" on the LCD), while still running a composite STL to the transmitter, it's a simple matter to build up (or buy) a precision audio oscillator and just mix 19 khz into the mono composite audio before the exciter to turn on the light. Yeah I know technically you aren't supposed to do that, but it works fine.

 

[rfry]

If you're that worked up about turning on the stereo light (or the little "ST" on the LCD), while still running a composite STL to the transmitter, it's a simple matter to build up (or buy) a precision audio oscillator and just mix 19 khz into the mono composite audio before the exciter to turn on the light. Yeah I know technically you aren't supposed to do that, but it works fine.

But doing so enables the L-R demodulator in analog stereo receivers, which adds noise to the L+R (monaural) audio that the receiver detects -- and for those receivers defeats much of the benefit of using monaural-only transmission.

//

 

[littlejohn]

Mr Fry is correct. You'd do as well to just run stereo. One AM in the Northeast used to put up the 5Hz tone which identified Kahn AM stereo, back in The Day. This fooled Crysler/Huntsvile OEM radios - and some others - into going to the wide IF bandwidth setting, and the station sounded mu ch better. Again the noise increased slightly, but that wasn't a great issue at the time in an automobile.

 

[boiseengineer]

Technically, just transmitting a 19 kHz "pilot" violates this little section:

Sec. 73.322 FM stereophonic sound transmission standards.

a) An FM broadcast station shall not use 19 kHz (+-)20 Hz, except as the stereophonic pilot frequency in a
transmission system meeting the following parameters:
(1) The modulating signal for the main channel consists of the sum
of the right and left signals.
(2) The pilot subcarrier at 19 kHz 2 Hz, must
frequency modulate the main carrier between the limits of 8 and 10
percent.
(3) One stereophonic subcarrier must be the second harmonic of the
pilot subcarrier (i.e., 38 kHz) and must cross the time axis with a
positive slope simultaneously with each crossing of the time axis by the
pilot subcarrier. Additional stereophomic subcarriers are not precluded.
(4) Double sideband, suppressed-carrier, amplitude modulation of the
stereophonic subcarrier at 38 kHz must be used.
(continues...)

 

[rrsounds]

Technically, just transmitting a 19 kHz "pilot" violates this little section:

Sec. 73.322 FM stereophonic sound transmission standards.

a) An FM broadcast station shall not use 19 kHz (+-)20 Hz, except as the stereophonic pilot frequency in a
transmission system meeting the following parameters:
(1) The modulating signal for the main channel consists of the sum
of the right and left signals.
(2) The pilot subcarrier at 19 kHz 2 Hz, must
frequency modulate the main carrier between the limits of 8 and 10
percent.
(3) One stereophonic subcarrier must be the second harmonic of the
pilot subcarrier (i.e., 38 kHz) and must cross the time axis with a
positive slope simultaneously with each crossing of the time axis by the
pilot subcarrier. Additional stereophomic subcarriers are not precluded.
(4) Double sideband, suppressed-carrier, amplitude modulation of the
stereophonic subcarrier at 38 kHz must be used.
(continues...)

If that was the case, every "stereo" station would be in violation whenever they transmitted a L+R only signal (such as an announcer's microphone).

Because, as stated previously, when comparing a mono signal transmitting a pilot versus a stereo station broadcasting mono material, the spectral content is (theoretically, at least identical.

Kind Regards,
David

 

[rrsounds]

If you're that worked up about turning on the stereo light (or the little "ST" on the LCD), while still running a composite STL to the transmitter, it's a simple matter to build up (or buy) a precision audio oscillator and just mix 19 khz into the mono composite audio before the exciter to turn on the light. Yeah I know technically you aren't supposed to do that, but it works fine.

But doing so enables the L-R demodulator in analog stereo receivers, which adds noise to the L+R (monaural) audio that the receiver detects -- and for those receivers defeats much of the benefit of using monaural-only transmission.

//

I would pick one nit here, Mr. Fry: the noise does not show up in the L+R signal, but rather, since the noise comes from the subcarrier region, appears out-of-phase in the individual left and right outputs. I'm pretty sure the noise would disappear if the two channels were summed.

Kind Regards,
David

 

[Tom Wells]

If you're that worked up about turning on the stereo light (or the little "ST" on the LCD), while still running a composite STL to the transmitter, it's a simple matter to build up (or buy) a precision audio oscillator and just mix 19 khz into the mono composite audio before the exciter to turn on the light. Yeah I know technically you aren't supposed to do that, but it works fine.

But doing so enables the L-R demodulator in analog stereo receivers, which adds noise to the L+R (monaural) audio that the receiver detects -- and for those receivers defeats much of the benefit of using monaural-only transmission.

//

I would pick one nit here, Mr. Fry: the noise does not show up in the L+R signal, but rather, since the noise comes from the subcarrier region, appears out-of-phase in the individual left and right outputs. I'm pretty sure the noise would disappear if the two channels were summed.

Kind Regards,
David

I remember summing the audio of a noisy FM stereo signal at the outputs of the audio amps years ago, and was amazed to find the noise reduction was exactly equal to the noise reduction in the mono position of the tuner. I expected the "true" mono from the tuner would be somewhat quieter.