Finally got the chance to hear WTMP in Tampa. This is the only AM music station I have heard in HD. Unfortunately, the audio was terrible in HD. There is no base and the treble is way too loud. It sounded very tinny. The analog sounds fine for AM. In addition, the audio stream is several seconds out-of-sync digital vs analog. Is it unusual for HD AM to sound so bad and out-of-sync from the analog signal?
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WTMP 1150
- Thread starter CentralFL
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The only time I heard music on HD AM was when a local Punjabi station left the HD on after purchasing the station. It sounded like FM, basically. There was some bass present.
The issue might be the radio you're using, or it's possible that they haven't bothered to dial in the EQ on the HD side.
The issue might be the radio you're using, or it's possible that they haven't bothered to dial in the EQ on the HD side.
This is one of my gripes with HD radio. It's a 20 year old standard now that desperately needs an update. In todays area and given the current luke warm response to HD that probably wont happen. Other digital radio standards out there are much more modern and flexible but obviously wont work inside the FM broadband band in their current form. Trying to maintain backwards computability with the current iBOC is likely not possible.
EQ can only do so much to fix a very old AAC codec and low bitrates. At very low bitrates it tries to make up for it with SBR but often adds annoying artifacts. Even in All digital AM mode you only get around 40 Kbps to work with for the entire channel. Doesn't mean it's all audio as well.
Assuming you don't have local noise a radio with a wide AM filter sounds much better.
On the FM side a few run 96 Kbps and it sounds decent enough for radio but you only get a single channel. It starts to get rather bad when try to cram 3 or 4 channels into a single iBOC channel.
As for the out of sync audio may have been that they don't have the time alignment set correctly.
There is little or no interest in AM HD, as there is not much interest in AM. Any improvement in FM HD (you don't specify whether you are referring to AM, FM or HD in general.
But the point is that this particular station does not sound good. AM HD does, in fact, sound better than AM analog. No, it does not compare well with FM HD, but it is in fact an improvement for its specific band.
What do you mean by "filter"? If you are talking about the tuner bandwidth, that can be determined in a number of ways depending on the circuitry.
You need to read up on FM HD. The "4th" channel is essentially a separate proposition. And the 3 base channels can be allocated bandwidth as deemed appropriate by the operator / licensee.
What do you mean by "time alignment"? Are you referring to the delay applied to the analog audio intended to match the digital audio?
If you are dealing with areas of broadcasting where you have no professional experience, you should present your concerns as questions first.
Not sure what improvement they could do to both really without moving it to a separate band to maintain backwards combability. I don't think they can just kill off current iboc and start with a new standard. There was petition awhile ago for 45-50 Mhz DRM+ but not sure if that went anywhere.
I disagree here. The artifacting and tinny highs just sound bad to my ears. If you have local noise however iBOC can clean that up provided it's not bad enough to prevent the sidebands from locking.
Radios that give you a option to adjust the filter. Some of course do this automatically. Eton Elite Satellit i have here gives me a few different filter lengths tho it's a DSP based radio. On a SDR if push it out to 10 Khz it sounds very good for AM imo. Local KSCO here during the day seems to use 10 Khz. 20 Khz if you count both sidebands.
Hum. I thought the 4th channel option was included in the base spec and you could run 4 channels at 24 Kbps. It appears that's not the case according to Multicasting - HD Radio and requires the use of Extended Hybrid mode. Regardless, the bitrates you can use there aren't very high so it wont sound very good.
Yes
I figured the topic of HD radio time delay is pretty self explanatory. You apply a delay to your HD streams so you don't have weirdly sounding audio if you flip between analog and digital. Products exist to keep it in alignment automatically.
HD channels can be separately allocated in accordance with the station's perceived needs. For example, a talk channel could have a lower rate than a music one.
True, But at the end of the day it's very limited bandwidth. You can only cram so much into 96 Kbps. Speaking about FM HD here.
I guess 32 Kbps is acceptable for talk and maybe 64 Kbps for music but still not great IMO. It's like crappy low bit rate internet streams. At that point I'd argue a well processed FM station and a radio such as the Sony XDR that offers good stereo separation would sound much better. There is probably some High end NXP chips now that are better in various car radios etc.
I guess the counter to that would be if you have multipath and/or picket fencing then HD radio likely might win out. That was presented as one of the advantages and probably still holds true there as it can handle fading and multipath.
If they could increase the entire channel to 256 Kbps or 384 Kbps it would be much much better and actually beat FM audio quality hands down.
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So I happened to have these videos pop up on my youtube suggestions again of old C-QUAM/AM Stereo demos that are fantastic. Obviously AM stereo was way before my time.
12.5 kHz audio bandwidth in these demos according to the description. so it wouldn't be possible get as high as a top end with AM broadcast being limited to 10 Khz in the US.
IMO these demos are far better then what AM iBOC does right now. While HD radio does have a higher top end due to SBR Spectral band replication - Wikipedia it just sounds harsh and artificial due to it being severely bit starved.
Figured it was relevant to post it here vs another topic.
Off topic for low bitrates some time ago I was impressed by the updated to the Opus codec https://opus-codec.org/examples/. Even at only 64 Kbps it sounds a lot better then AAC. it's also open and royalty free compared to AAC. In the case of HD radio HDC which was found to be be very similar to AAC.
12.5 kHz audio bandwidth in these demos according to the description. so it wouldn't be possible get as high as a top end with AM broadcast being limited to 10 Khz in the US.
IMO these demos are far better then what AM iBOC does right now. While HD radio does have a higher top end due to SBR Spectral band replication - Wikipedia it just sounds harsh and artificial due to it being severely bit starved.
Figured it was relevant to post it here vs another topic.
Off topic for low bitrates some time ago I was impressed by the updated to the Opus codec https://opus-codec.org/examples/. Even at only 64 Kbps it sounds a lot better then AAC. it's also open and royalty free compared to AAC. In the case of HD radio HDC which was found to be be very similar to AAC.
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At the time of analog AM stereo, there was no 10 kHz limit. The problem was that litigation delayed the introduction of the system in the US from an anticipated late 1978 or early 1979 to the early 1980, and by that time most music listening had migrated to FM. In addition, most major market FMs covered their area much better than the majority of local AMs so the band was lost before AM stereo even began to roll out.
Again, Before my time but didn't FM stereo also play a part in this? A bit of a shame as AM stereo seemed like a very good standard but for crappy reasons it never took off.
If we had 15 Khz AM stereo and good processing it seems like it would have sounded nearly as good as a FM station with good processing.
I wonder what the future holds for the AM band. Seeing KGO having a sudden format change doesn't bode well for it's future.
On a sidnote. Not a broadcast engineer so please excuse me if my terms are off. It seems like a FM station that sounds good with dynamic range is hard to find now. When you do though it sounds amazing and can appreciate the work put into it as care was taken. To me it seems processing these days seems to be compress the daylights out of it to get to remain at max allowed peak deviation at all times. Goes hand in hand with the loudness war I figure. This probbaly isn't an engineering choice but people above them that said it has to be as loud as others...
FM stereo began almost exactly 20 years before AM stereo was finally authorized. By around 1977, more than half of all listening was to FM, and an even higher percentage of music listening was on the "new" band.
It didn't because most AM radios were not capable of doing much better than 5 to 6 kHz of audio.
KGO dies around the time of the 2008 recession. It was getting old in appeal, and the PPM showed it had no cume depth.
Yeah, That doesn't sound surprising.
I wonder how KCBS-AM is looking now that the old KGO is gone. Both have a good day groundwave signal down here tho it isn't exactly local. I guess it's a given that it's a 50kw blowtorch
At night KCBS seems to get me some weird phase distortion. My guess is a combo of skip and groundwave.
Guaranteed this was recorded under ideal conditions with expensive equipment, and has possibly been sweetened.
I owned a C-Quam radio back in the day (pricey Kenwood head unit in the car). Even worked at a C-Quam radio station, with the requisite professional off-air stereo monitor in the control room, and nothing ever sounded that good.
For one thing, there was always audible background hiss that is not heard in that recording. Also, the platform shifting was real, and it was annoying.
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