I have a project coming up that may go digital, what would be the quality hit for doing multiple channels, would it be possible to do an hd2 and hd3 music and hd4 be a low bandwidth talk channel ? This is what was asked of me by the owner.... I've had exactly 0 experience with hd radio..
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how many channels on hd radio at acceptable quality
- Thread starter stephend2
- Start date
I think the question is answered simply in asking: what is the lowest bitrate that you can operate a sub-channel with?
I had heard that you can even sacrifice bandwidth on the HD-1 channel to run upwards of 4+ sub-channels. That would make me wonder why bother, as lowering the bandwidth of the HD-1 could possibly make it sound worse than an analog FM transmission.
I had heard that you can even sacrifice bandwidth on the HD-1 channel to run upwards of 4+ sub-channels. That would make me wonder why bother, as lowering the bandwidth of the HD-1 could possibly make it sound worse than an analog FM transmission.
There is 96 kbps to play with. IIRC, if you add an HD2, the HD1 drops to 48 kbps (which is inferior to analog FM IMHO). The HD1 doesn't go any lower - what happens is the 48 kbps left over gets divided by the number of HD and/or data channels you do.
So...if you have an HD1 and HD2, both will be 48 kbps. Add an HD3 and the HD2 will drop to either 24 or 36 kbps depending on the bandwidth you choose for the HD3.
Again, remember that 48 kbps (IMHO, though others may disagree), is already inferior to the potential quality an analog FM signal is capable of.
So...if you have an HD1 and HD2, both will be 48 kbps. Add an HD3 and the HD2 will drop to either 24 or 36 kbps depending on the bandwidth you choose for the HD3.
Again, remember that 48 kbps (IMHO, though others may disagree), is already inferior to the potential quality an analog FM signal is capable of.
From wikipedia page on HD Radio. I'm assuming just like anything digital, the higher the bitrate, the less robust the signal is. Would it be possible to run the higher bitrate if the signal was sufficient for the market? I suppose this would require testing. 150kb/sec is a lot better than 100kb/sec when you consider that 48kb/sec is the minimum acceptable for music programming. I'll go along with that based on my experience with HE-AAC, I would not want to listen to any less, I believe I could make that sound decent.
Being a big non-fan of HD Radio (only because it will not ALL fit in +/- 75khz like analog does), that's the way my ears heard it years ago. Good to know my ears were also hearing the same "inferior to analog sound" as LA_Guy when an HD2 was present.LA_Guy said:
I seem to remember one of the stations in Philadelphia is running an HD4 program. Is a road trip in the budget? 
PTBoardOp94 said:I seem to remember one of the stations in Philadelphia is running an HD4 program. Is a road trip in the budget?
Doesn't one of the stations near Pittsburgh also do an HD-4..
My assumption is to keep the most important material on the fist two HD channels. Keep voice only on the 3rd.
Of course one must ask themselves who listens to HD radio?
I know how that sounds asking that, but it's a good idea to keep in mind. Sub channels have always been the place to put uninteresting things.
You have to consider who will be listening to begin with. There is such a small population that listens to HD channels. Kind of reminds me of the days of subcarrier programming for the blind.
No offense but 1/100 of your listeners may even know what a HD2 channel even is, or that HD radio exist.
If you're going to put something on there, make sure it's specialized and important to the group that want's it to exist in the first place.
Of course one must ask themselves who listens to HD radio?
I know how that sounds asking that, but it's a good idea to keep in mind. Sub channels have always been the place to put uninteresting things.
You have to consider who will be listening to begin with. There is such a small population that listens to HD channels. Kind of reminds me of the days of subcarrier programming for the blind.
No offense but 1/100 of your listeners may even know what a HD2 channel even is, or that HD radio exist.
If you're going to put something on there, make sure it's specialized and important to the group that want's it to exist in the first place.
I hate how HD radio sounds. Even with all the bits on a single channel. My ears are extremely sensitive to compression artifacts. I think regular FM sounds FAR better than that 96k stream...
Personal opinion, but it's why I could never listen to satellite radio. It was extremely irritating to hear all that lossy *crap*.
Personal opinion, but it's why I could never listen to satellite radio. It was extremely irritating to hear all that lossy *crap*.
chriscollins said:
I agree, on both accounts.
If they've used AAC LC (which is not HE-AAC more widely known as AAC+, but rather a more generic perceptual coder) than 96kbps could sound better than FM. But they are not. Instead, they are using a codec similar to HE-AAC. And just like HE-AAC it relies on SBR to artificially regenerate the high end. Because of that HE-AAC always has that gritty, metallic sound to it. And since it artificially regenerates the high-end in the decoder, HE-AAC can never be audibly transparent. Unlike AAC LC (on which HE-AAC is based on) that can be transparent at bitrates at above 128 kbps.
As far as satellite radio is concerned, they've allocated way too small bitrates for their channels, again based on this false premise that HE-AAC is such wonderful and technologically advance codec that you can cram "CD quality audio" in something like 32 kbps... And some manufacturers like Orban, still proclaim this. Which, I personally find very disappointing.
Regards,
Goran Tomas
HE-AAC sounds great at low bit rates for what it is.. but of course it won't be CD Quality... I've done A / B flips between decent sounding internet streams and a lot of actual FM and there is not much difference from a 48kbps HE-AAC internet stream [that's processed properly and isn't using poor source material) and some FM broadcasts in the car.
Going back to HD .. You can make it sound "ok" if you take great care... however most do not.. their feeding mp3 source audio into not properly set up processing into a low bit rate HD-2 or HD-3 .. and when you add all that together you get a mess!
Going back to HD .. You can make it sound "ok" if you take great care... however most do not.. their feeding mp3 source audio into not properly set up processing into a low bit rate HD-2 or HD-3 .. and when you add all that together you get a mess!
Goran Tomas said:
I'm glad I'm not the only one who hears this the same way. You put a good adjective to it with 'metallic'. My brain is wired to compression for some reason. I can see it in Television as well.
Recently, a local affiliate made their sub-channel HD. Prior to that, when the sub was in SD, their main carrier looked great. Now, it looks 'soft' and 'blocky'.
I know TV is a different beast, but it makes me wonder... How many other people hear it the way I do? Especially women. They are so much more sensitive and perceive high frequency energy differently. I wonder how HD Radio comes off to a group of 25-45 year old women? I'm sure the 12-17 would think it's good, as they have grown up on bit reduced material.
This may be straying from the topic a bit, but maybe it's time to start thinking about taking the FM channel largely digital, protecting only
a 15 kHz channel in the center for a mono analog signal. allowing some backward compatibility for existing receivers. Stereo would be digital only. SCAs would go away.
I haven't a clue as to how much digital bandwidth could be added in such a scheme...
a 15 kHz channel in the center for a mono analog signal. allowing some backward compatibility for existing receivers. Stereo would be digital only. SCAs would go away.
I haven't a clue as to how much digital bandwidth could be added in such a scheme...
chriscollins said:
I wonder that as well. But nobody is doing the research... The results could be surprising!
On one of the conferences I attended, there was a presentation on the results of an extensive test on the perception of the perceptually coded material. There is this huge myth that young people are so accustomed to perceptually encoded music, that they don't notice the difference to linear audio, or even, that they prefer the coded versions. Well, this blind listening test with students, completely debunked this assumption.
If enough independent research is done, the perception on encoded audio quality might be quite different than what the codec and product manufacturers like us to believe...
Regards,
Goran Tomas
joebtsflk1 said:
There is a system proposed to do this - it was called FMeXtra, now VuCast. With keeping a mono part of the MPX, you'd get about 150 kbps digital channel. Which is more than enough for a high quality digital simulcast, that would sound better than FM. With 128 kbps AAC LC, you could claim "CD quality" and have some credibility.
But due to bad business moves and focus on the wrong market (analog SCA replacement), it never really picked up. Although it could have been a very good (if not better!) alternative to HD Radio/IBOC system.
Regards,
Goran Tomas
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