AM Stereo | Hacker News Reader

AM Stereo

amstereo.org

79 pointsLeoPanthera39 comments

I hadn't thought about AM Stereo in a long time. I had an old car with a 2nd hand "Voxson" AM Stereo unit in it, the stereo light would light up on 2CA (in the ACT in the late eighties). Unfortunately for AM stereo, Australia didn't really have widespread FM stations outside of the major cities until a similar period and the hype was all about FM.

Australia is huge and AM radio stations were able to broadcast much further than the first FM stations, so if you were looking for an FM station on a long trip you'd be fiddling with the radio trying to find another station, even with new-fangled digital tuners and seek functions.

I suppose it didn't help that AM stereo, in practice, was somewhat underwhelming compared to FM when you could find it, especially in a noisy car with a pair of sun damaged 6" speakers and the windows down because you didn't have A/C.

For those curious about the specific modulation: https://en.wikipedia.org/wiki/C-QUAM

Sounds like it was dead on arrival because of FM band.Reminds me of Thomson MP3pro's proprietary audio format that didn't take off either.

https://en.wikipedia.org/wiki/Mp3PRO

You could play an mp3pro 64kpbs with any regular mp3 codec and it sounded bad as expected, but using mp3pro codec it artificially improves it by recreating higher frequency harmonics that were removed due to the low bitrate and compression. Edit : typos and precision.

> Sounds like it was dead on arrival

How can something that is still in deployed commercial use for many years be “dead on arrival?” Moreover, AM stereo came out long after the FM band was well established.

*HD-DVD noises*

Whatever you thought that meant.

Because being niche when you were positioned to go mainstream is a failure.

mp3PRO and HE-AAC work in essentially the same way, but AAC is more efficient.

https://en.wikipedia.org/wiki/High-Efficiency_Advanced_Audio...

It wasn't DOA because of FM. FM stereo predated it by decades.

It was a combination of factors:

1) poor noise rejection of AM

2) high noise on the AM band

3) changing programming on AM (aka the rise of talk radio)

I think this is the webpage of one of my favorite YouTubers VWestlife: https://www.youtube.com/channel/UC1ydE9gDHTdvbNVIgEKIKzw He makes all sorts of cool retro videos on computers, hi-fi systems, records, tapes, etc. And he's been doing it for a really long time too! Like, recording early stuff on camcorders and digitizing and uploading.

Yup.... he namedropped it in one of his latest video's, that's probably why it was posted here now.

AM Stereo with a wide-IF receiver will pass 13khz of audio, it sounds quite good when it's clean. As does regular AM, on a vintage radio with a wife IF, it can sound great.

I worked at a Top 40 station WISE AM in Asheville,NC in the 70’s & 80’s. When we went Stereo in the early 80’ we gave away Sony AM stereo transistor radios on the air. The crazy part was hearing lightning static in stereo. I still have one of those Sony radios in a display case in my home office.

Back in the day, 1984, when I was an electrical engineer trainee, I was seconded to the electronics repair shop for the summer at the steelworks where I worked. I got to choose a kit to build and I chose this one from local magazine based on the Motorola kit. I think I intended to integrate it with a car radio. I don't think I got it to work all that reliably. Only a few of the music AM stations seemed to pick it up here in Australia. Very quickly FM won out. http://messui.polygonal-moogle.com/sch/kits/AMstereoEA.pdf

Contrary to what article says you can sometimes hear an FM radio station under ‘skip’ conditions. You can sometimes hear stations from the U.S. South in Upstate NY.

It's known as tropospheric ducting or propagation, where an ionized channel forms in the atmosphere which can reflect radio. Waveguides above the clouds. Under unusual conditions it can enable very long-distance UHF/VHF. Analog TV has been sporadically received out to over 1000 km. As I understand, pulling it off is harder with digital modes, as they're generally quite sensitive to phase variations caused by multipath distortion.

There are two phenomena.

Tropospheric ducting happens at low altitudes, a lot of times in the summer across Lake Ontario, people in Canada tune into TV stations in Syracuse and I sometimes talk to them on a 2 m repeater south of Cayuga lake.

The other is a ‘skip’ caused by a dense spot in the ionosphere.

Ham radio enthuasists take advantage of unusual propagation but so do many people who like listening to commercial broadcasts from far away.

In '97 I bought a '96 Mustang and had an AM station on for some reason; maybe a Cubs game. I was shocked to hear stereo effects come out of the speakers, and then I looked at the LED display on the radio and saw a little "headphone" icon. Sure enough, the stock Ford radio had AM stereo.

Cool novelty, but in the end it was the same AM sound quality but with two channels. A worthy improvement though.

> it was the same AM sound quality but with two channels

This conflicts with the website. It says the sound quality of AM Stereo is as good as FM.

An AM channel can pass 12-13khz of audio an FM channel about 19khz, they sound dramatically different though because of different equalization curves. AM stereo sounds nearly as good as FM, while also feeling "richer".

It sounds like the marketing for AM Stereo focused on the wrong things.

Really they should have stressed the range (so more station choice in more places) and the jump in fidelity rather than the stereo bit.

Convenience over quality worked for VHS vs Betamax. It could have worked for AM Stereo too.

Kinda, as I pointed out on a parallel thread, it failed for a variety of reasons.

First thing is the early AM Stereo radios didnt sound very good, mostly because of the narrow IF (a heavy rolloff over 8khz), but there were other inherent issues with AM that it didnt attempt to immediately solve too, like poor quality noise blankers.

Later on they intrigued the AMAX AM Stereo Radios did solve a bunch of quality issues with AM -

1) Wider IF (meaning more fidelity)

2) Much improved noise suppression

3) Other improvements improving platform stability (meaning preventing stereo center from shifting left-right.

If failed because:

1) poor noise rejection of AM and naturally high noise on the AM band

2) changing programming on AM (aka the rise of talk radio)

3) delay in the FCC picking a single AM Stereo standard, they decided to "let the market chose" which means for like 6 years there were multiple mutually incompatible AM Stereo standards on the air, which reduced incentives by receiver manufacturers to introduce support.

I don't recall anyone ever claiming that it was truly comparable in fidelity to FM. In addition to bandwidth limitations, AM is still subject to way more interference than FM.

Maybe in a perfect lab setting it could approach FM, but... yeah. ¯\_(ツ)_/¯

I'm really far away from any of the stations listed but I'd imagine cheap modern SDR can get this and decode it pretty easily. Anybody try?

Ben from Oddity Archive tried to track down a few of these stations over the summer to see if they actually were still broadcasting in stereo https://www.youtube.com/watch?v=i8b8Ro1OdQ8

If you view the source code for that page, you'll note that the HTML tags are in all caps. The very first line is:

<!DOCTYPE HTML><HTML><HEAD><META CHARSET="windows-1252">

I'd not expect an HTML5 doctype. More like ol' <!DOCTYPE HTML PUBLIC "-//SoftQuad//DTD HoTMetaL PRO 4.0::19971010::extensions to HTML 4.0//EN">

Uhm... https://en.wikipedia.org/wiki/Digital_Radio_Mondiale ?

Both DRM and iBiquity HD-Radio are mentioned on the page.

Maybe longwave can make a come back with digital modulation. There's a ~100 kbit/s broadcast channel available way down there, with uniquely excellent propagation characteristics. (Viewing radio as a wave, at such long wavelengths, when the radio waves encounter buildings, or even mountain ranges, they diffract around them. It's like how most of the energy of a wave on the surface of some water diffracts around a small rock sticking out of the water, rather than being stopped by it.) A single transmitter can cover most of a continent, with indoor and even some ground penetration. Receivers are simple, and can have tiny antennas despite the wavelength. There are even watches that can sync themselves to longwave time signal broadcasts, which are about the only thing on LW currently broadcast in North America.

Got to watch those 100ft full-wave whip antennas when going under the bridge ;)

This website is targeted at the US/Canadian audience, where HD Radio is used rather than DRM. HD Radio does exist for AM stations, but has failed to catch on even more than it has failed for FM (which is a pretty sad story). In my market, for example, there is only a single AM station with HD that's receivable... and that's probably better than the average. It's a Spanish-language sports station, so it sort of falls into two of the popular AM brackets.

In 2020 the FCC went ahead with adoption of "all-digital" AM stations with no analog audio. There are enough advantages to the all-digital arrangement, which is of course much more similar to DAB, that some people think it might breathe a little life back into HD radio - I'm skeptical, but only time will tell.

In general AM radio has little popularity in the US outside of news and sportscasting. Foreign language stations are also a bit of an AM holdout since they benefit from the larger catchment area.

Now I'm not sure that I agree with the authors criticism of IBOC HD Radio as unproven, it works quite well these days, but it is clear that remarkably few radio receivers on the market have HD radio support... even in expensive hi-fi and home theater receivers. Where HD radio has been fairly successful is in cars, with HD radio being a fairly common but far from universal feature in car head units.

HD Radio uptake is quite variable by market. In some markets it's quite dense, others not do much.

Other than slightly worse stereo separation FM Multiplex sounds better, other than the stations running the whole HD channel for one audio stream.

Title was submitted as "AM Stereo" but was munged by HN.

You can edit it back.

I don't know how, there's no Edit button.

I think it disappears after a certain time.

Fixed now.

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