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WCBS-am: Analog on IBOC stations doesn't have to sound bad

L

LinoNYC

Guest
Here in NYC there is a large difference in how the analog audio is handled, some such as WOR opt for the narrow bandpass approach while others such as WABC and more recently, WCBS-am sound alot closer to wideband AM.

While you can hear that there is some peaking in the 6khz region, the scratchy distortion that is an artifact of steeper rolloffs on narrower stations is gone.

http://www.sendspace.com/file/4jfj66 14mb wav

Lino
 
Not living in NY - I haven't heard WCBS audio. But I've heard the analog from many IBOC. Even tuning as carefully as I can - making sure the alignment of the radio is dead on - I still hear IBOC hiss in the background. Some stations worse than others, but there on all of them. There is only one possible answer - unless the phase of the transmitting antenna system is completely FLAT across the whole range - the phase modulated sidebands will have an analog modulation component.
 
rbrucecarter5 said:
Not living in NY - I haven't heard WCBS audio. But I've heard the analog from many IBOC. Even tuning as carefully as I can - making sure the alignment of the radio is dead on - I still hear IBOC hiss in the background. Some stations worse than others, but there on all of them. There is only one possible answer - unless the phase of the transmitting antenna system is completely FLAT across the whole range - the phase modulated sidebands will have an analog modulation component.
Click to expand...

Additionally, part of the loud "white noise" stereo HD AM signal is -26 directly under the 0 to 5kHz analog audio.
 
SUPERCASTER said:
rbrucecarter5 said:
Not living in NY - I haven't heard WCBS audio. But I've heard the analog from many IBOC. Even tuning as carefully as I can - making sure the alignment of the radio is dead on - I still hear IBOC hiss in the background. Some stations worse than others, but there on all of them. There is only one possible answer - unless the phase of the transmitting antenna system is completely FLAT across the whole range - the phase modulated sidebands will have an analog modulation component.
Click to expand...

Additionally, part of the loud "white noise" stereo HD AM signal is -26 directly under the 0 to 5kHz analog audio.
Click to expand...

That is one of your "golden oldies" Realistically, Am under the best of conditions can achieve a 30db/sn.

Even on a fairly wideband tuner (KLH) that aircheck evinced a noise level well below what the average person and radio would even notice.

Lino
 
LinoNYC said:
Even on a fairly wideband tuner (KLH) that aircheck evinced a noise level well below what the average person and radio would even notice.
Click to expand...

Remember, if you let your station's audio chain deteriorate too far - noise adds by the root sum squared law, meaning that the strongest source of noise tends to dominate the noise figure. If that source of noise is your station, then receiver quality is moot.

This may explain the difficulty with nighttime IBOC - the strongest source of noise dominates. If that is IBOC hash, it will push through clearly, masking all other noise sources.
 
HD supporters claim the average listener is incapable of noticing improved fidelity, then claim HD radio will be the salvation of terrestrial broadcasting, and HD radios are "flying off the shelves".
How can both be true?
Obviously, they can't. Neither statement is true.
 
Well Supercaster, of course I don't think typical listeners are "incapable of noticing" improved fidelity. But let's be honest here. Sadly, most AM radios are low-fidelity devices, with bandwidth barely better than a telephone. I KNOW that many aren't, and that analog am is capable of great fidelity. But if your radio takes a nosedive above 2khz, then you probably are "incapable of noticing" fidelity improvement related to wider bandwidth. Actually YOU (the listener) are not "incapable of noticing". Your radio is incapable of revealing the difference. Let's be real, there ARE some REAL limitations to the fidelity potential of typical AM radio listening, because many (most perhaps) radios are so damn bad!
 
Mike Walker said:
Well Supercaster, of course I don't think typical listeners are "incapable of noticing" improved fidelity. But let's be honest here. Sadly, most AM radios are low-fidelity devices, with bandwidth barely better than a telephone. I KNOW that many aren't, and that analog am is capable of great fidelity. But if your radio takes a nosedive above 2khz, then you probably are "incapable of noticing" fidelity improvement related to wider bandwidth. Actually YOU (the listener) are not "incapable of noticing". Your radio is incapable of revealing the difference. Let's be real, there ARE some REAL limitations to the fidelity potential of typical AM radio listening, because many (most perhaps) radios are so damn bad!
Click to expand...

The old "most AM radios are narrow bandwidth" lie. I thought Shredderman had debunked that one for good: http://www.mindspring.com/~shreddermanrulz/myth1.htm
 
Yes, there's no absolute cutoff at, say, 3-5khz. But a device that's down 20-30db by 6-8khz, as most AM radios are, is NARROWBAND. You can't hear highs. Sibilant sounds are muted. Things like brushed cymbals, and tinkling bells all but disappear. This is real, and obvious. OBVIOUSLY we need better AM radios! Adherence to the NRSC pre-emphasis/de-emphasis should have been MANDATORY (rare is the FM radio that doesn't follow the de-emphasis curve closely).

But the combination of muffled highs (which manufacturers claim is to reduce interference...ok, it does actually do that) and rolled-off lows (w.t.f.? This is UNNECESSARY by any standard!) results in audio more akin to a telephone than anything "high fidelity" in too damn many AM radios. If your response curve looks like an upside down smiley curve, peaking in the midrange, and drooping at either end, then it DOES make discerning differences in fidelity at the station difficult.

In my own tests with an rf generator, I have found many AM radios in my house that can reach 8khz. But at this frequency the level is VERY attenuated in all but items like the GE SuperRadio (and the Radio Shack clone), and the Sony SRF-A100. As Orban pointed out in the 80s, it IS POSSIBLE to get 8khz audio out of typical AM radios, but it requires such extreme equalization that loudness is compromised, which of course compromises coverage, and "dial presence".
 
Mike Walker said:
Radio Shack clone), and the Sony SRF-A100. As Orban pointed out in the 80s, it IS POSSIBLE to get 8khz audio out of typical AM radios, but it requires such extreme equalization that loudness is compromised, which of course compromises coverage, and "dial presence".
Click to expand...

Uh - Mike - read Shredderman's page. Every radio he analyzed was extremely wideband. It would seem to not only be possible without "extreme equalization" - but downright easy if you put in one miserably cheap ceramic filter for the IF. Nobody in their right mind would suggest AM radio manufacturers are using this approach to make their radios "high fidelity". But poor selectivity brings along, as a side benefit, wideband audio response. What was it he claimed - +/-40 kHz? Why don't they just make the AM section an antenna, tuning cap, and diode and be done with "cost cutting"? Not only wideband audio, but no power wasted on the AM section.
 
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