"List Of Tuners That Can Properly Filter HD Radio Self Noise?"

[PocketRadio]

"List Of Tuners That Can Properly Filter HD Radio Self Noise?"

"... As you settle back to enjoy it, you notice something peculiar. The normally pristine audio from a station that prides itself on a high-quality signal has an annoying background noise. You check your directional rooftop antenna, but it's aimed right at the station not more than ten miles away. Your tuner's signal-strength meter is pegged to the right, as usual. What gives? Then you vaguely recall that the station recently announced it was converting soon to HD Radio."

http://www.ham-radio.com/k6sti/hdrsn.htm

 

[scanman1]

None of my analog tuners have a problem with HD on FM. AM, OTOH, is another story.

 

[Mike Walker]

And the term "self-noise" refers to noise generated BY THE RADIO, not the radio station. It's an incorrect use of the term. Not to burden you with facts.

 

[w9wi]

And the term "self-noise" refers to noise generated BY THE RADIO, not the radio station. It's an incorrect use of the term. Not to burden you with facts.

The noise is *generated* by the station -- turn off the digital transmitter, and it goes away. True, it's only *audible* because the receivers are sensitive to signals on frequencies they don't need to be sensitive to.

It does seem a bit naive however to suggest that the audience replace (or modify!) millions of existing receivers to accomodate a technology that virtually none of them are using. (ironically, *DXers* are probably the single group that's most likely to have followed Beezley's suggestions - many of us have implemented IF Filter mods, often going as low as 110KHz)

The rules in place at the time these receivers set aside these areas of the FM channel as interstation "guard bands". The receiver designers believed in good faith there would be no significant energy in these areas.

(thanks to the OP for posting that link; the author has a very good reputation in the amateur radio community for technical expertise, and the article is both comprehensive and understandable, at least to hams!)

 

[Mike Walker]

Post me a recording of this alleged "noise" being received on an FM tuner. I'm surrounded by FM HD stations from the west, south, and east. I've tried HARD to hear any interference on adjacent channels, and I'll be damned if I can. And I'm talking about on ANALOG radios...expensive and cheap. I'm not saying it DOESN'T exist, but if it's such a problem, would it follow that people like me...who have worked in and around radio for decades...can't find it if they try? And I HAVE TRIED!

I've READ that when receiving a station with HD on the very cheapest analog fm stereo radios, that signal to noise can be compromised. I've READ it, but again...I'll be damned if I can HEAR IT!

Again, I'm referring to FM. I have NO AM HD experience...yet. I do have a suspicion that interference won't be so hard to find.

 

[Play Freebird]

As discussed in the referenced article, the noise problem is usually confined to stereo receivers that use older decoder chips and/or wide filters. I've noticed the background hiss on my early '60s-vintage McIntosh MR65B tuner, as well as my favorite portable: a Sony SRF-40W FM Walkman, which still sounds incredible (on good headphones) even though it's a 26 year-old-design. I'd estimate the HD-induced noise is down about 50 dB, so it's somewhat masked by heavy processing, but I can certainly hear it. Modern receivers perform better, it's not an issue on my JVC HD car radio.

Mike, I know from reading your profile that you became fascinated with radio at a young age after listening to FM stereo headphones. Same deal here! If you can find one of these old Walkmen, I think you would enjoy it, if you can still find a station transmitting a clean signal.

I always bring my "antique" SRF-40W when I travel overseas (it has analog tuning, so it's not locked to the 200 kHz channel steps found in North America) and always enjoy listening to FM in parts of the world where quality is still valued over "quantity". A couple of years ago, I spent a night in Dortmund, Germany and happened to catch a concert broadcast on WDR 3, one of the regional public radio services. This was an in-house recording, and with the acoustics of the hall, it just sounded fabulous -- and yes, I got goosebumps. From old-fashioned un-hyped FM radio, no less!

This experience was a reminder of Major Armstrong's original vision, but it's a shame I had to travel 4000 miles to hear it.

 

[dbdigital]

As discussed in the referenced article, the noise problem is usually confined to stereo receivers that use older decoder chips and/or wide filters. I've noticed the background hiss on my early '60s-vintage McIntosh MR65B tuner, as well as my favorite portable: a Sony SRF-40W FM Walkman, which still sounds incredible (on good headphones) even though it's a 26 year-old-design. I'd estimate the HD-induced noise is down about 50 dB, so it's somewhat masked by heavy processing, but I can certainly hear it. Modern receivers perform better, it's not an issue on my JVC HD car radio.

Mike, I know from reading your profile that you became fascinated with radio at a young age after listening to FM stereo headphones. Same deal here! If you can find one of these old Walkmen, I think you would enjoy it, if you can still find a station transmitting a clean signal.

I always bring my "antique" SRF-40W when I travel overseas (it has analog tuning, so it's not locked to the 200 kHz channel steps found in North America) and always enjoy listening to FM in parts of the world where quality is still valued over "quantity". A couple of years ago, I spent a night in Dortmund, Germany and happened to catch a concert broadcast on WDR 3, one of the regional public radio services. This was an in-house recording, and with the acoustics of the hall, it just sounded fabulous -- and yes, I got goosebumps. From old-fashioned un-hyped FM radio, no less!

This experience was a reminder of Major Armstrong's original vision, but it's a shame I had to travel 4000 miles to hear it.

I know what you mean.

I have some old air checks going back to 1969 that I recorded of KWST in Los Angeles (now Power 106) using a mid-60's Fisher FM stereo tuner and Sony reel-to-reel tape deck. Of course, very little processing was used in those days and the sound is amazing.

Puts the analog sound found on many of today's FMs to shame.

db

 

[Mike Walker]

Hey "Play Freebird". Great name! I'm old enough to have been on the air when the phone rang a hundred times a night with that very request "HEY, PLAY FREE BIRD, MAN!"

The oldest FM Stereo Walkman-type radio I have is a GE that I bought in 1980 because I really liked the features...switch selectable stereo/mono switch, separate left and right volume controls, good ole' analog tuning, and a really nice AM section (response doesn't "drop like a rock" above a couple of khz). I don't hear the noise you're talking about on this unit.

The Walkman I use more often is a Sony SRFM35 with digital tuning. I still don't hear the noise. The oldest FM stereo device I own is a 1960s Fisher model 500c receiver. It's out of commission now (bad tube), but when I get it fixed, I'll give a listen. I'm VERY interested to hear what the hell people are talking about, because I hear NO noise. I've even had a friend at an HD station cycle the HD on and off while I listened for a change in background noise on an analog radio. NOTHIN' (with the volume cranked up enough I could hear the background hiss either way...in other words, too damn loud).

I have read that s/n ratio on some old radios can suffer as much as 20db, but it must be pretty rare because I can't duplicate it, and I've tried!

Back to your comment about falling in love with FM stereo nearly 40 years ago, listening through headphones...HD gives me the same feeling of "hearing more than I've ever heard before" that I had then. Which is a lot of why I love it. I even end up listening to programming I don't especially care for, because the audio is so good (I've been doing that with tv as well...we just got our first HDTV. I've actually been watching golf and tennis, WHICH I HATE! But it looks fantastic!)

 

[Play Freebird]

The FM self-noise is subtle, likely to be masked under music if the station is using heavy processing, but it can usually be heard under voice. (On the other hand, the AM HD noise on some receivers is horrendous. I know someone who recently bought a VW Jetta with the "Monsoon" audio system; its AM section has wider-than-average IF response, so all of the HD stations are underlaid with hiss. Needless to say, the non-HD stations which aren't using a 5 kHz filter sound MUCH better... so much for "compatibility".) Now, back to FM:

Yesterday, I ran a side-by-side comparison between my old analog FM Walkman and the Accurian HD receiver while listening on Sony 7506 headphones. The Walkman was fed a strong signal from an external attic antenna by capacitively coupling the center conductor of the coax to the headphone cable, I used the same antenna to feed the Accurian.

In terms of audio signal/noise ratio, HD beats analog, no question. During pauses, the noise floor is way down (on good source material)

But for natural, musical, human-compatible sound, I still prefer FM. Nearly every station in the Philadelphia market runs an HD-2 secondary channel, so the main channels are allocated only 64 or 48 kbps, causing the HD Codec to struggle on the high frequencies. Although the HD channel's lack of pre-emphasis limiting provides a slight boost in brightness, the timbre of the harmonics is phony, like the difference in taste between cane sugar and "Sweet N' Low".

I don't see any remedy for this problem until the "full digital" system is implemented and the available bitrate increases. But that's not likely to happen for 15 or 20 years. The scary thing is that some broadcasters are now talking about adding HD-3, which will crunch the bits even further.

So I ask the question: With this "HD" system, has audio really taken a step forward, or are we just moving sideways -- or even backwards?

 

[R.F. Burns]

The FM self-noise is subtle, likely to be masked under music if the station is using heavy processing, but it can usually be heard under voice. (On the other hand, the AM HD noise on some receivers is horrendous. I know someone who recently bought a VW Jetta with the "Monsoon" audio system; its AM section has wider-than-average IF response, so all of the HD stations are underlaid with hiss. Needless to say, the non-HD stations which aren't using a 5 kHz filter sound MUCH better... so much for "compatibility".) Now, back to FM:

Yesterday, I ran a side-by-side comparison between my old analog FM Walkman and the Accurian HD receiver while listening on Sony 7506 headphones. The Walkman was fed a strong signal from an external attic antenna by capacitively coupling the center conductor of the coax to the headphone cable, I used the same antenna to feed the Accurian.

In terms of audio signal/noise ratio, HD beats analog, no question. During pauses, the noise floor is way down (on good source material)

But for natural, musical, human-compatible sound, I still prefer FM. Nearly every station in the Philadelphia market runs an HD-2 secondary channel, so the main channels are allocated only 64 or 48 kbps, causing the HD Codec to struggle on the high frequencies. Although the HD channel's lack of pre-emphasis limiting provides a slight boost in brightness, the timbre of the harmonics is phony, like the difference in taste between cane sugar and "Sweet N' Low".

I don't see any remedy for this problem until the "full digital" system is implemented and the available bitrate increases. But that's not likely to happen for 15 or 20 years. The scary thing is that some broadcasters are now talking about adding HD-3, which will crunch the bits even further.

So I ask the question: With this "HD" system, has audio really taken a step forward, or are we just moving sideways -- or even backwards?

In NYC we have 2, HD 3 channels, WNYC & WPLJ. I've sent a recording of WNYC HD2 to Mike. Ask him for his impressions of their HD 2 stream.

 

[Mike Walker]

I'd say quit listening with your eyes (bitrate specs), and listen with your ears. Bitrate figures are not comparable to mp3, because HDC is a far more efficient codec. If it sounds good, it is good. If you're biased against lossy compression algorithms (as some obviously are), the only way to PROVE the quality of them is with double-blind testing.

96kbps HDC is completely transparent. If no aggressive compression or limiting is applied, it sounds just like the source. 48kbps still sounds brighter, cleaner, less distorted, and with far better stereo separation and bass extension than typical analog fm stereo.

 

[Play Freebird]

96kbps HDC is completely transparent. If no aggressive compression or limiting is applied, it sounds just like the source. 48kbps still sounds brighter, cleaner, less distorted, and with far better stereo separation and bass extension than typical analog fm stereo.

In a perfect world, we wouldn't need lossy algorithms and could transmit everything at 24 bit/96k linear -- however, I understand the need to compromise. The question is: How much can we throw away and still claim it sounds "better than analog". I agree with you that the 96kbps HDC sounds good, but I easily hear the artifacts at lower rates, especially if the audio is heavily processed ahead of the encoder.

I'm hoping that some local DTV stations start offering high-quality audio services within a few years. They have *much* more bandwidth available for ancillary data than HD radio and could do some really cool things with surround sound, etc.