Pew: "We Stand By Our Research On HD"

[rbrucecarter5]

To find all the low bandwidth AM radios, you need to include ALL radios not just cheap Chinese portables.. Find me a modern car stereo, OEM or aftermarket, with more than 5 kHz on AM. I can't find one. I checked the small handful of radios at Best Buy just yesterday (while looking for HD, which they NO LONGER SELL in standard DIN radios) and none of them sounded better than a telephone on AM.

I've already stated that car radios have decent selectivity - more of a requirement in a car radio than a home / portable radio. I suspect a lot of the "selectivity" is audio equalized for talk and sports. Thankfully Pioneer and some of the other high end aftermarket radios are not doing that any more, and just incorporating speech equalization into the audio controls, giving you the choice on AM.

Most car radios appear to be directly sampling AM and not using superhet architecture at all. Something only recently possible - I doubt it was done 10 years ago.

 

[Chuck]

A quick way to make AM sound a lot better would be to rescind the NRSC Mask, and allow stations to do 15 KHz in the daytime and 9.5 KHz at night, analog only. Yes, it would splatter onto adjacent channels in the daytime, but the spectral energy wouldn't be any more than is currently allowed for HD. In fact,it would probably be considerably less on most program material. At least, it wouldn't be a constant noise, like the digital hash of HD. Besides, the AM-HD contingent argues that hardly anyone tries to listen to a first adjacent anyway. Two can play that game.

Before somebody says "How do you make the frequency response change?" Easy. Most modern processors can be day-parted to do whatever you want. If you could "fix" an AM station by the installation of an Omnia 1 or a BW Broadcast DSP-AM processor, that would be a real bargain.

 

[davideduardo]

A quick way to make AM sound a lot better would be to rescind the NRSC Mask, and allow stations to do 15 KHz in the daytime and 9.5 KHz at night, analog only.

The problem is that most AM receivers in use today can't "hear" that additional bandwidth. The NRSC committee headed by Bob Orban demonstrated a few years ago that the average consumer radio rolls off at least 10 db at 3.9 kHz and that anything above 6 to 7 kHz bandwidth only makes the listening on most radios worse...

 

[Chuck]

The problem is that most AM receivers in use today can't "hear" that additional bandwidth. The NRSC committee headed by Bob Orban demonstrated a few years ago that the average consumer radio rolls off at least 10 db at 3.9 kHz and that anything above 6 to 7 kHz bandwidth only makes the listening on most radios worse...

Actually, many radios can do it. See some of R. Bruce Carter's posts. He's right.

As the new owner of an AM station, I recently dug out an old Sony radio that sounds amazing on AM. The GE Super-Radio can do it too, as can many others. But even if the receiver can't do full bandwidth, there is still an improvement in the perceived sound quality as long as the additional bandwidth isn't just a bunch of noise. In the daytime, noise isn't as big a problem as at night, which is why I suggested narrowing response after dark. You can demonstrate the effects of full bandwidth audio versus narrow band audio fairly easily. Just use a a lo-fi speaker (like a cheap computer speaker) and run music through it that has been filtered (200 Hz - 3.5 KHz). Then compare the same speaker using full bandwidth music audio (50Hz - 15Khz). Just about any audio editing program can do that for you. Decide for yourself which sounds better on music. Unless the speaker in question is really, really terrible, I'll bet you choose the full bandwidth version.

In fact adding high frequencies that most humans can't hear has an effect on your perception of audio quality. Maybe you can't hear it, but you can feel it. The people who make Mackie mixers noticed that and include an additional very high frequency EQ control they call "Air." I was skeptical myself, but it does make a difference. Psycho-acoustics is an interesting topic.

 

[rbrucecarter5]

A quick way to make AM sound a lot better would be to rescind the NRSC Mask, and allow stations to do 15 KHz in the daytime and 9.5 KHz at night, analog only.

The problem is that most AM receivers in use today can't "hear" that additional bandwidth. The NRSC committee headed by Bob Orban demonstrated a few years ago that the average consumer radio rolls off at least 10 db at 3.9 kHz and that anything above 6 to 7 kHz bandwidth only makes the listening on most radios worse...

Really? You still make that nonsensical statement even in the light of massive evidence to the contrary? Sad --- you have bought the lies hook line and sinker.

 

[satech]

The problem is that most AM receivers in use today can't "hear" that additional bandwidth. The NRSC committee headed by Bob Orban demonstrated a few years ago that the average consumer radio rolls off at least 10 db at 3.9 kHz and that anything above 6 to 7 kHz bandwidth only makes the listening on most radios worse...

IIRC, that testing was done using only a handful of current-production receivers, none of which were especially cheap (and thus would be inherently wideband due to the lack of selectivity) or purposely designed for hi-fi AM (such as a GE/RCA Superadio III). And given a clean signal playing music, the test listeners did show a preference for a full 10 kHz transmitted bandwidth, but that was mostly overlooked in the final conclusions.

 

[rbrucecarter5]

The problem is that most AM receivers in use today can't "hear" that additional bandwidth. The NRSC committee headed by Bob Orban demonstrated a few years ago that the average consumer radio rolls off at least 10 db at 3.9 kHz and that anything above 6 to 7 kHz bandwidth only makes the listening on most radios worse...

IIRC, that testing was done using only a handful of current-production receivers, none of which were especially cheap (and thus would be inherently wideband due to the lack of selectivity) or purposely designed for hi-fi AM (such as a GE/RCA Superadio III). And given a clean signal playing music, the test listeners did show a preference for a full 10 kHz transmitted bandwidth, but that was mostly overlooked in the final conclusions.

Doesn't anybody bother to read my posts and web pages? It isn't the expensive AM receivers that are wideband - it is the $5 cheap radios that are wideband (or the $1 bill of material for the AM radio section of something that includes a radio). NOBODY will pay for a wideband, high fidelity AM radio, so nobody makes one on purpose, except maybe the CCrane-EP. They are just wideband because the ceramic filter is incredibly sloppy and wide.

If listeners prefer wideband music, they won't be listening to it on AM. They long ago switched to FM. The wideband nature of new AM sections is an accident, not intentional. Just cost reduction - scale down the IF selectivity by buying a cheap ceramic filter - to squeeze another penny out of the design.

 

[Chuck]

Doesn't anybody bother to read my posts and web pages? It isn't the expensive AM receivers that are wideband - it is the $5 cheap radios that are wideband (or the $1 bill of material for the AM radio section of something that includes a radio). NOBODY will pay for a wideband, high fidelity AM radio, so nobody makes one on purpose, except maybe the CCrane-EP. They are just wideband because the ceramic filter is incredibly sloppy and wide.

If listeners prefer wideband music, they won't be listening to it on AM. They long ago switched to FM. The wideband nature of new AM sections is an accident, not intentional. Just cost reduction - scale down the IF selectivity by buying a cheap ceramic filter - to squeeze another penny out of the design.

Yes, I read your posts and you are right. Given good signal strength to overcome man-made interference, it would be easy to make AM and FM sound almost indistinguishable from each other on these cheap radios. That would require AM stations to improve their frequency response, rather than rolling things off at 3.5 KHz.

 

[rbrucecarter5]

Doesn't anybody bother to read my posts and web pages? It isn't the expensive AM receivers that are wideband - it is the $5 cheap radios that are wideband (or the $1 bill of material for the AM radio section of something that includes a radio). NOBODY will pay for a wideband, high fidelity AM radio, so nobody makes one on purpose, except maybe the CCrane-EP. They are just wideband because the ceramic filter is incredibly sloppy and wide.

If listeners prefer wideband music, they won't be listening to it on AM. They long ago switched to FM. The wideband nature of new AM sections is an accident, not intentional. Just cost reduction - scale down the IF selectivity by buying a cheap ceramic filter - to squeeze another penny out of the design.

Yes, I read your posts and you are right. Given good signal strength to overcome man-made interference, it would be easy to make AM and FM sound almost indistinguishable from each other on these cheap radios. That would require AM stations to improve their frequency response, rather than rolling things off at 3.5 KHz.

I've been doing some research about the 6 transistor AM reference design. I now think maybe it is more appropriate to call it the "All Japanese 6 transistor" design because it was Sony that first put the pre-driver transformer - then push pull class B stage, then output transformer on the audio - thus making the first of the soon to be standard 6 transistor radio design. This happened in about 1957 to 1958, so TI did the first four transistors - they had the luxury of a 22.5V battery, so one audio transistor driving an output transformer gave plenty of output voltage swing. Not sure what the battery life would have been in the Regency, though. That would be pure class A and drain the battery pretty quickly if you left the volume on high. Sony's first try was five transistors and not much better, but it ran off of 9V. They followed it up with the familiar 6 transistor configuration that was easier on batteries.

Of course this is a nostalgic trip down memory lane. I wonder when the last such radio was actually made? I'm not including the necessary additions for FM, just the AM section. I'd bet it hung on in Russia a lot longer than the US. But I'd be surprised if one had been made within the last 30 years. Maybe somebody sold it as re-branded surplus circuit boards from an earlier product.

I am still interested in the exact list of radios from the NRSC study, with dates of manufacture and preferably schematics. Either the study was incredibly corrupted by wanting to support a conclusion, or incredibly lucky to find a bunch of antiques. I'd like to know their source - I'm getting short on germanium transistors to repair really old gear. Either way, most radios today are broadband, I think I have proved that beyond any reasonable doubt. I challenge anyone to find an AM section with three familiar cans in it - yellow, white, and black - with the familar red oscillator can. Send me a picture good enough to read date codes on the parts. I don't think you will find out from the 80's, maybe you would from the 70's. If you can, I know it will have an IF bandwidth in the 3 to 4 kHz range. Old tube All American Five radios only have two IF cans and are inherently broader band than transistor radios for that reason. But when you are only driving a 2 1/4 inch speaker, broadband doesn't mean a lot so transistor radios used three. And the main reason as far as I can tell is impedance matching and allowing two IF gain stage transistors because it was harder to get germaniums to the same gain as tubes.

 

[davideduardo]

Given good signal strength to overcome man-made interference, it would be easy to make AM and FM sound almost indistinguishable from each other on these cheap radios. That would require AM stations to improve their frequency response, rather than rolling things off at 3.5 KHz.

And, given that in the top 100 markets, less that 175 stations cover even 80% of the whole market, day and night, there simply are not very many AM stations that are capable of giving adequate service.

The very few remaining HD stations roll off at between 5 kHz and 6 kHz, while the rest are theoretically NRSC compliant, meaning they occupy a 10 kHz bandwidth... not 3.5 kHz.

 

[davideduardo]

Doesn't anybody bother to read my posts and web pages? It isn't the expensive AM receivers that are wideband - it is the $5 cheap radios that are wideband (or the $1 bill of material for the AM radio section of something that includes a radio).

You are missing the point... nobody buys stand-alone radios today, cheap or otherwise. They get radios as part of another device, if at all.

I'm always fascinated that the reference radios mentioned are things like the GE Superradio or some other ultra-niche product not intended for the mass market.

Most of the home or office radios in use today are existing units that likely have not been in production for a decade or more. As distribution changes to new media, they are not being replaced.

 

[davideduardo]

Really? You still make that nonsensical statement even in the light of massive evidence to the contrary? Sad --- you have bought the lies hook line and sinker.

The NRSC committee headed by Bob Orban (I get the feeling that some of the posters have no clue as to who Mr. Orban is) purposely selected radios that would be in consumers hands... not new production models exclusively... but the kind of thing being used by consumers.

Today, so few of the newer models are being sold, if you can even find a radio at a store, that their characteristics are totally irrelevant.

 

[rbrucecarter5]

The NRSC committee headed by Bob Orban (I get the feeling that some of the posters have no clue as to who Mr. Orban is) purposely selected radios that would be in consumers hands... not new production models exclusively... but the kind of thing being used by consumers.

Today, so few of the newer models are being sold, if you can even find a radio at a store, that their characteristics are totally irrelevant.

I know exactly who Mr. Orban is. He would not be the first, nor will he be the last, to publish information influenced by money. I am not intimidated by titles or reputation in the industry. When bias is apparent, reputations are meaningless. Conclusions reached before the study was done, or experimental procedures specifically targeted to support a desired conclusion is not science. I personally value my scientific integrity higher than some people. Double blind, properly conducted, unbiased experimentation that produces repeatable results is science.

Even at the time of the study, it had been 20 years at least since a three IF can AM radio had been produced. I have no idea how they picked their radios, but the radios they selected obviously had a very high percentage of antiques.

 

[Chuck]

To quote NRSC

"The audio envelope input spectrum to the AM transmitter shall be -15 dB at 10 kHz, smoothly decreasing to -30 dB at 10.5 kHz,
then remaining at -30 dB from 10.5 kHz until 11.0 kHz. At 11.0 kHz, the relative amplitude shall
be -40 dB, smoothly decreasing to -50 dB at 15 kHz. Above 15 kHz, the relative amplitude shall remain
below -50 dB. The reference level is 1 dB above a 200 Hz sine wave at 90% negative modulation."

 

[TheBigA]

I have no idea how they picked their radios, but the radios they selected obviously had a very high percentage of antiques.

The study is online, and they give full details on how they reached their conclusions.

 

[rbrucecarter5]

I have no idea how they picked their radios, but the radios they selected obviously had a very high percentage of antiques.

The study is online, and they give full details on how they reached their conclusions.

Link? The link somebody posted here was conclusions with no list of radios. Of course the list without schematics wouldn't be much use. They need to document the equipment used in the test to support their conclusions.

 

[rbrucecarter5]

I have no idea how they picked their radios, but the radios they selected obviously had a very high percentage of antiques.

The study is online, and they give full details on how they reached their conclusions.

This is a link to the design of antique radios manufactured from the 1950's through early 1970's:

http://www.angelfire.com/planet/funwithtransistors/AJ6-1.html

A study based on these radios will conclude that bandwidth is 3 to 4 kHz.

Here is a link to what is typically inside radios manufactured in the last 30 years:

http://www.earmark.net/gesr/Current_Radio_Design.htm

A study based on modern radios will conclude that bandwidth is 10 to 40 kHz.

 

[TheBigA]

Link? The link somebody posted here was conclusions with no list of radios.

There are a bunch. Just search NRSC AM study. The ones I saw all list specific radios tested, and detail the methodologies.

 

[rbrucecarter5]

I'll do some research on this list and see what is up. I very strongly suspect that the roll off is done in the audio stages, not the IF stages. There is a huge difference between IF bandwidth and audio roll-off. Audio roll-off alone does very little to get rid of adjacent channel interference, or to get rid of HD sideband noise - especially if you can't tune precisely on channel. And if you ever do manage to get precisely on channel, the peculiar warbling sound caused by slight sideband asymmetries will definitely fall into the audio response of all test receivers. It is annoying!

 

[satech]

When bias is apparent, reputations are meaningless. Conclusions reached before the study was done, or experimental procedures specifically targeted to support a desired conclusion is not science.

The HD Radio proponents requested an NRSC study to validate the practice of reducing analog AM bandwidth that implementation of AM IBOC necessitated. That is what they wanted, and that is exactly what they got. No surprise there.

The only consequence is that the NRSC ended up recommending 7 kHz bandwidth, because even the most die-hard AM IBOC proponents realized that 5 kHz bandwidth (the original IBOC spec) sounds like total crap, even on narrowband receivers.