I don't live in any of the markets, but regularly get skywave listening in my car in HD after dark from WBZ Boston, WCBS NYC and WLS. That, and some of the naysayers here keep transposing the signal qualities of an AM-HD signal when talking about FM-HD signal. Two completely different modulation models and transmission methods.
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I don't live in any of the markets, but regularly get skywave listening in my car in HD after dark from WBZ Boston, WCBS NYC and WLS. That, and some of the naysayers here keep transposing the signal qualities of an AM-HD signal when talking about FM-HD signal. Two completely different modulation models and transmission methods.
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diymedia
Guest
Sticks and stones! I find it telling that, 12+ years on from formal launch, we're parsing the minutiae of IBOC's technical performance, as if it's some new-fangled technology that we're still unraveling the mysteries to. Lover or hater, can we at least agree that it's these inconsistencies in design and implementation that have stymied (in part) broadcasters' interest in adopting HD?
I wouldn't say the adoption of investing-in or transmitting IBOC/HD is solely, or even primarily based on technical concerns. At least I've never heard that argument anywhere but here.
Especially for mid or small market stations, the limitation is really just the pure implementation costs verses Return On Investment for a station which may be comfortably profitable, all the way to stations who are just squeaking by with their analog signals alone. Had consumers embraced listening to those "special and unique" commercial-free formats on FM, to the point where future revenue was involved, or AM listening started to skew younger and increase, stations in any market would be climbing on board in droves. In my mind the problem was related to lack of substantive marketing that was appealing. Most of the large original station groups that invested in HD/IBOC, were under the impression that promoting HD on the station that carried HD was a good idea. Well, I suppose it was from an expense standpoint, but not in a way that interested consumers. Marketing of HD was cryptic and obtuse, assuming somehow that listeners to their stations would be intrigued, running out to purchase a new aftermarket radio or insist that their new car was equipped with HD reception capability. Clearly that didn't happen. I think that had the original station group investors and Ibquity put together a serious war chest of wide ranging marketing campaign dollars outside of their owned stations, interest in HD may have at least gotten off the ground by now.
I agree. AM Stereo was probably promoted more than HD radio has been. DAB in Europe is marketed more effectively than HD radio has been marketed in America. Here in the U.S. I don't know anyone but radio aficionados that even know HD radio exists. However, I have non-radio aficionado acquaintances in Scandinavia that have DAB radios in their houses.
Of course, their governments over there have helped in marketing by publicizing the services... even so, there was a much better marketing campaign overall.
Here in the U.S. I don't recall much advertising of new HD services on TV or even radio.
The only time I hear HD "marketed" now is when the HD-2 is casually mentioned during station IDs and liners. I don't think that's enough to get consumers interested.
35-40 miles?
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rbrucecarter5
Guest
I am glad it works for you. My experience is a little different listening to music. The music even with a good signal on a local station, perfect HD lock sounds like a high bandwidth digital stream. High frequency content like cymbals are strangely frequency shifted down. Music quality was much poorer than the same station, same song, a few months earlier with C-Quam. Granted, you probably can't hear those effects on talk radio. But from what I have heard, as a discriminating music listener - HD AM is not an improvement over C-Quam, and the use of HD AM pretty much relegates the band to talk and sports formats. Music formats do not sound like analog FM, as was originally advertised.
Even with talk radio, analog AM radios sound really good, because the IF bandwidth of today's radio is so wide. If the audio response wasn't artificially rolled off in the audio stages, mono talk and music would sound GREAT on AM! I would advise anybody listening to talk or music on a modern AM radio to take one capacitor out of the audio signal chain and enjoy wideband AM mono. I have some radios without that audio roll off, and even talk radio sounds rich and full fidelity. Much better than the same station in AM HD. You may not immediately notice audio compression artifacts on speech, but your mind can, and I find digital AM fatiguing to listen to - without being conscious of the compression.
AM Music in HD? Sounds better than AM music in analog...that's what matters.
(It's better than MP3 quality and most people that's good enough and has been an example of how discriminating people are.)
Neil Young is proposing a new music player with (supposedly) superior audio. Want to predict how well it well sell?
http://en.wikipedia.org/wiki/Pono_(digital_music_service)
Sorry, we are not moving backwards...as nostalgic as it might be.
You think HD has had a hard time? Try convincing the masses that music really does sound good on the AM band!
(I won't hold my breath)
That's because the Pono player is dependent on a bunch of snake oil to earn its sales. I'm actually a believer that with current technology we could benefit from increased fidelity from a move to 48 kHz/24-bit lossless recordings from the current CD-standard 44.1/16, but the truth is the CD standard already encompasses 100% of normal human hearing range, as well as a dynamic range great enough to cause severe ear injury if the entire range is used.
Anyone who claims that a $10,000 network cable or a 192 kHz/24-bit recording sounds any better than the same stuff at CD rates through $5 cables is succumbing to confirmation bias. I've yet to meet anyone who could tell a 192/24 recording from a 44.1/16 recording or a thousand dollar speaker wire versus lamp cord in a blind test. I am one of those cursed with particularly critical hearing and have passed to some degree ABX listening tests between 44.1 and 48 kHz recordings of vinyl albums on consumer grade equipment, but anything beyond that is a waste of space and marketing voodoo. And this is coming from someone who wanted to believe high definition recordings would be something special, and owns several (freebie) high res audio tracks for testing purposes.
That said, AM HD is in no way comparable to mp3 in encoding quality. A 320 kbps mp3 is nearly transparent from a critical standpoint and de facto transparent to the vast majority of listeners. An AAC (.m4a), OGG Vorbis or Opus (new open source codec) at comparable bitrates will be even more transparent, as will a FLAC (lossless compressed) audio file.
The sames of AM HD I've heard online put it somewhere around a 64 kbps mp3 encoding, which no one even uses anymore because it sounds so bad. FM HD with no subchannels is more or less equivalent in my experience to a 112 to 128 kbps mp3 but only with the newer software and hardware installs. And none of those come close to sounding anything close to CD-quality.
It's a matter of opinion whether one thinks AM HD or a fully uncompressed digital audio chain to an analog AM stereo transmission will sound better, because both have trade-offs. AM HD has compression artifacts galore and sounds swishy on the (faked) high end, while AM is bandwidth limited to, er, 12 kHz? Something like that. But I'd rather have 12 kHz of clean audio than 20 kHz top end that's full of artificial computer noise that is supposed to approximate the sound of a hi-hat or cymbal, or vocal inflections.
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rbrucecarter5
Guest
That's my point. And that you won't hear 20 kHz. High frequencies are aliased and frequency shifted down - the "geniuses" that designed the system ignored the Nyquist frequency. If you ever did try to broadcast music with substantial high frequency content, the frequency shifting of those frequencies downward would make the music unlistenable. Wideband mono is much preferable, at least the percussion instruments appear at the correct pitch.
Nyquist Sampling Theorem has nothing to do with stereo or mono, but is about the sampling frequency (time or space). Every digitally-created or digitally reproduced audio has some form of aliasing, simply because trying to mathematically sample such a complex signal containing multiple frequency layers is impossible at fixed rates required for reproduction of the audio. HD/IBOC Radio, Mp3 files, Wave files, CD's, DVD's, etc., whatever your form of reproduction, must have a fixed sample rate which will cause aliasing, particularly at high frequencies. According to the Nyquist sampling theorem, the signal must be sampled at twice the highest frequency contained in the signal. Say you have a sine wave at 3Hz, fc=3 Hz, and so the Nyquist theorem tells us that the sampling frequency, fs, must be at least 6 Hz. Taking a 20kHz sine wave by itself, the sample rate would have to be 40kHz. Next we assume the sampling of a complex signal composed of many frequency components. By Fourier's theorem, any continuous signal may be decomposed in terms of a sum of sines and cosines at different frequencies. Since the many frequencies in music can't be sampled individually, a fixed rate is chosen. In the case of CD's, the rate is 44.1kHz. One common situation in which aliasing occurs is in Film. This is because continuously varying images are being discretely sampled at a rate of 24 frames/sec. The Nyquist sampling theorem tells us that aliasing will occur if at any point in the image plane there are frequency components, or light-dark transitions, that occur faster than fs=2, which in this case is 12 frames/sec. But in many situations the light-dark transitions may be occurring faster than this, such as a wagon wheel or propeller rotating at high speed. The point being; even with modern or classic films, some form of aliasing occurs.
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Everything in life has trade-offs...
(BTW...How are you going to get AM Analog in Stereo?)
C-QUAM is the standard and I have an AMAX Walkman sitting here unloved with nothing to listen to, so…
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rbrucecarter5
Guest
Nyquist has to be slightly greater than 2:1, otherwise you could get a dropout if the sine wave happened to be in zero-crossing when sampled twice. I think the original CD players used 22.1 kHz, and were ridiculously expensive because they needed a multiple pole filter to prevent the sample rate from heterodyning with musical notes. Faster A/D converters made oversampling possible. And made a great marketing tool - when in reality all it did was get rid of the expensive 20 pole low pass filter and substitute much simpler and cheaper filters.
The problem I see with AM HD is how they can possibly get a high enough sampling frequency in the limited bitrate they have. The audible evidence - and I MAY have it on tape - is that things like cymbals and triangles are undersampled, and curiously pitch shifted way down in frequency (the result of undersampling). If I had to guess, I would say their sampling rate is something more like 5 kHz, not 22.1 kHz. Does anybody know the real sample rate? That isn't going to work for anything but talk radio and sports, but guess what? That is what most AM is these days. But one listen to a music station and you come away underwhelmed. I don't know how anybody could think that musical beds in talk shows sound good. Unless they roll off their music, those undersampled musical instruments are going to be VERY annoying.
As for stereo - it has been pointed out that many, if not most HD radios decode C-Quam, which is why it would be a viable alternative for music stations. At the very least, it appears that HD radios have to use product detection for HD AM, which is much superior to envelope detection. So even if all the HD radio does is receive mono - analog, it is going to sound really good. Since there is no reason for stereo on talk or sports stations, why not just go for wideband mono analog and sound great on HD radios in mono? Musical beds? The local talk station hosts complain that if they play too much music, the owner complains. So you get a few seconds of mono music instead of stereo - people are there for Rush or whatever, they aren't music listeners.
I'm not sure what the sample rate for IBOC/HD-AM encoders are, as that isn't published by Ibquity. That being said, I believe what you're mistaking for sampling rate artifacts, are probably CODEC artifacts. Even more with AM-HD at the lower 40kbps bitrate, the effects of running music or spots that were recorded or transcoded and played as Mp3 or AC3 files, don't sound very good (swishy). I've heard AM-HD stations play .wav file at 44.1 that sounded really good. If WLW or WCBS plays a spot that was encoded as an Mp3 for file size or whatever, it is noticeably more swishy. FM-HD requires a 44.1 encoder input for the best quality, even then the station can limit the audio low pass to 15kHz to conserve bits. The Orban dual analog/digital audio processor for HD stations runs a sample rate of around 512kHz, because of look-ahead limiting of peaks rather than traditional clipping. Clipping audio waveforms doesn't work well with HD encoding, since there is a limited number of bits available to spare because of clipping byproducts.
I've got two HD-capable radios in vehicles, and neither will decode AM stereo. Not sure where you heard that. Since AM stereo has been dead and gone for over 25 years now, I couldn't imagine why any receiver manufacturer would bother.
The same can be said about IBOC except it's only been dead since 2007.
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The theorem says the sampling fate must be AT LEAST MINIMUM twice the highest frequency..in TDM/T1s/ISDN, the sampling rate is 8kHz for a 0-4 kHz frequency range on a DS0. With an 8bit rate, that makes each DS0 64kb/s....x 24 plus overheaed for framing and signaling and you get 1.544MHz for a T1....ROLM telephone switches used 12 kHz in their early models (because ROLM, which started making flight computers for the DOD and moved into the telecom side, could only get access to control chips which sampled at 12 kHz and not the telecom industry 8 kHz....a ROLM CBX offered better quality on its audio vs a Nortel or other brand) but this hurt them as converting to T1 took up an entire shelf of cards to do the conversion....The later IBM designed 9751 ROLM did switch to 8kHz sampling...and the audio quality was noticable.
As for mono vs stereo, OEM radio makers will NOT accept customer complaints about noise, etc, hence, this is why FM blends LONG before the stereo pilot is lost and AM quality is so poor....they DON'T want customers coming back to the dealers complaining...
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