Pulling Good Analog Sound out of Severe HD "Self Noise"?
 

I just found out my local classical station "uses the Extended Hybrid Mode for HD Radio, which allows us to allocate up to 120 kbps total for all our digital channels combined. We currently only broadcast two channels, our main (HD-1) at 64 kbps, and our secondary channel Viva la Voce (HD-2) at 48 kbps." This must be the worst case for cramping the bandwidth of the analog channel and is almost certainly killing my old tuner with "HD self noise."

I'm looking for guidance on two questions:

1) Is it even possible to get really good sound from the analog channel of such a station?

2) If so, what are the best tuners for the job? I'd guess the IF band-pass would have to have very steep edges -- a digital tuner might be indicated -- but doesn't this imply higher distortion? Other factors? -- Clark2

1.) Yes
2.) Look for a tuner with a good post-detection filter. Narrow IF's with steep slopes will help but also add to distortion as you've noted.

Some of the best performing tuners are :

Sony XDR-F1HD
Sangean HDT-1

They use DSP stereo decoding and have very good HD self noise rejection.

Brian Beasley has a lot of good information on HD self noise on his website:

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


Did you run FMFool to see if you have a strong adjacent channel HD station?

If you have a strong HD adjacent, it will impact your tuner choices as you'll need a tuner with a lot of IF stages and sharp cutoff ceramic filters. Something like the MR 80 or Sansui TU-X1 will fill the bill. The Magnum Dynalab tuners, as good as they are, just won't work as well in that specific situation.

While Brian Beasley has done about all that can be done with HD he cannot defy the laws of physics. There is no way to obtain high fidelity from HD radio broadcasts with the available bit-rates. Brian is pretty much a 'voice in the wilderness' in his opinions on the SQ of HD (though I admit to having stopped reading his treatise some years ago - :beatinghorse:).

Yes, it is.

I'm not sure that a digital tuner offers any automatic advantage here. W9TR's suggestion of the McIntosh MR80 is a good one, and the MR80 is very much an analog tuner even though it has a digital readout. My MR80 still sounds great after all these years.

But having a strong adjacent channel with HD isn't imo the biggest problem, because the HD on your desired signal is likely to be just as big a problem.

Quality FM reception has always hinged a lot on location and the antennas, and that's still true. The better the receiving antenna, the higher the gain. The higher the gain, the less you'll notice the distortion inherent in a higher selectivity tuner.

If you are open to other options, have you considered streaming non-local classical radio stations that are streaming at higher rate bps? KDFC for example, streams at 128k. Or subscribing to a music service and create your radio stations based on music that you like?

That's interesting! I never would have guessed it. Why would that be the case; not enough gain in the internal RF stages? -- Clark2

About (2), can you then use a wide IF pass-band if the post-detection filtering is good enough, and get rid of the self-noise without increasing distortion?

I don't think there's any problem with adjacent HD. The nearest that I know of is 2.4 MHz away. Will check...

Thanks for the good information. -- Clark2

Don't the HD sidebands actually overlap the bandwidth of an adjacent channel? Is it possible to overcome that even with a narrow IF? -- Clark2

Yes, there is overlap into the first adjacent. The extent to which narrow IF filters will help that hinges on a lot of variables - that's the nature of FM reception. But consider that while the first adjacent channel is just 200 kHz away, the FCC typically spaces stations in any market by 400 kHz. To be fair, with today's crowded FM band (in the US), that doesn't always quite work in practice.

Correct - the sidebands of first adjacent HD channels can become 'on channel' interference. Which is why it is so important to understand your local listening conditions. If you have any first adjacent channel issues then the problem is really hard to fix because of the on channel interference.

Narrow IF's help here, as does a directional antenna used to put the offending station in a null.

The easiest test to see if you have HD self noise is to switch your tuner to mono. If the noise goes away in mono, you have HD self noise or the signal you are receiving is not full quieting in stereo anyway. You need about 20 dB more signal strength to get full quieting in stereo vs mono. That's exclusive of HD self noise.

Tom