HD radio is standard on a ton of automotive infotainment systems and the sound quality is a little better than what most listeners likely experience on a streaming service.
Does that still hold true? Internet streaming bitrates and codecs were abysmal early on, but 128 to 256 kbit/s HE-AAC and AAC-LC streams have become much more common from my perspective. I actually wrote the KROQ CE and PD about 4 years ago, asking why they were still streaming at only 64 kbit/s instead of going to (or offering as a "super HD" alternative) a higher, codec-transparent bitrate, to take advantage of the fact that streaming video platforms had "shoestretchered" most ISP service tiers into permitting high, nearly/totally unlimited bandwidth, even on cellular providers. I basically pointed out that in the years prior, datacenter bandwidth had dropped to near zero in cost, and consumers meanwhile were sitting around watching Youtube videos, television shows, and movies via their ISPs for hours on end, even over 4G, at bitrates ranging from ~600 kbit/s (360p) to 1+ mbit/s (various levels of HD) without any regard to the bandwidth factor, because most providers had stopped cutting peoples' throats for high usage levels. So why not go to 160 or above with AAC-LC and sound fantastic? Anyway, back then, the KROQ CE and PD didn't seem to agree with my logic, but years later, I noticed that their stream for KROQ HD2 had been given a facelift to 128 kbit/s HE-AAC (see for yourself with ffmpeg or your favorite player:
http://playerservices.streamtheworld.com/api/livestream-redirect/KROQHD2AAC.aac). And at least when I check out various other sources these days, it seems many others have finally seen the light I saw half a decade ago, and are following suit.
Which to me means that online streaming definitely sounds better than IBOC -- and by a mile.
For what it's worth, I was never able to stand the sound of IBOC and actually resented the fact my car tuner had no way to be manually set in analog mode. Maybe I would have found it acceptable in a car (with help from road noise masking) if I were listening to a station dedicating its entire ~94 kbit/s to its HD1 (i.e. no HD2 or above). But every station that I ever listened to in HD had an HD2 (or more) and was always unlistenable to my ears, even with background to help mask the flawed audio's details.
I wonder if the radio industry, today, has lost sight of the apparent fact that IBOC was never designed to utilize these bitrates forever. The "~94 kbit/s ÷ [number of channels]" predicament we're still in was surely meant to exist only during a brief transitional phase, wherein they expected rapid uptake of HD radios, followed by the shutting down of analog, allowing IBOC's bitrates to go much higher. But that hasn't happened. And at this point, I can't imagine the public ever replacing enough of their analog-only tuners (now that it has moved on to being interested primarily in "devices") to permit shutting the analog signals off -- especially with fractions of ratings points mattering. So it seems like IBOC has become stuck in "everything above 2 kHz sounds gritty and slushy" land.
Which leads me to this. The latest O&O processors (among others) have made substantial improvements in their analog HF clarity and fidelity since IBOC was introduced. Is it possible to configure an IBOC encoder to not encode an HD1, so that tuners always grab the main audio from the analog signal, leaving the HD2 service (and above) to hog all the digital bandwidth for themselves? If this was in fact possible, then that is how I would run my stations -- if I owned a cluster or two. At the height of the processing wars, the radio industry nitpicked over every half-decibel of loudness, and fretted over every half-decibel of audible distortion. Entire careers and fortunes were made (Bob's, Frank's, etc.) inventing miraculous techniques to mask distortion vs. the desired loudness levels of the day. Why, then, the radio industry doesn't see hugely audible IBOC codec artifacting as today's uncancelled clipper distortion blows my mind. I see codec artifacts as "distortion uncanceled coding." To me, broadcasting 30 kbit/s HD1+HD2+HD3 is the equivalent of driving pre-emphasized treble 12 dB deep into a diode in 1955. And even then,
at least analog clipping is made of
harmonics and sum/difference
inharmonics that are
somehow related to the audio going non-linear. Coding artifacts, by comparison, sound completely artificial. They're also worse because they're continuously present whereas analog clipping is only audible during the particular milliseconds something is going over the clipping threshold. With all that in mind, I would have to think -- and again, especially with what the latest analog processing can do to keep the HF sounding competitive with digital -- that any sane station with a compelling non-afterthought product on its HD2 should be trying to turn off its HD1 in order to revolutionize the sound of the HD2 in the same way the Optimod 8100 revolutionized the sound of loud analog FM by canceling away all
its audible distortion. Because, again, it just seems like an analog shut-off is never going to happen on FM. And without that shut-off, doing what I'm proposing (if possible) would be the second best thing, in terms of finally getting away from the horrid temporary IBOC bitrates we're all hearing.
P.S. I always sort of suspected these temporary bitrates (~94 kbit/s ÷ [channels]) may have been why IBOC's designers and the main processor manufacturers apparently came to an agreement whereby each HD waveform would be limited to -6 dB except for short-term transients (and possibly slightly less leaning on the multiband compression), with tuners playing the HD output +6 dB louder than the analog whenever they switched back and forth. It's almost like they needed to force every HD signal to sound "noticeably more alive and punchy" spectrum-wide to impress lay listeners as a distraction from how gritty and slushy its high spectrum actually sounded -- again, during the low bitrate transition period. I mean, yes, the HD also lacking the HF energy loss caused by the analog's pre-emphasis limiting would have also been impressive by itself. But had that been the
only audible improvement, people's attention would have been drawn directly to and
only to the very part of the audio drowning in artifacts. So I always figured that the 6 dB headroom allotment was agreed upon to help sell the system during its difficult transition period -- to make the codec noise medicine go down. Because once the analog finally did go away (and the bitrates went up), I always figured that at least one station in every market would eat that entire 6 dB in order to achieve 200% loudness vs. its format's competitor, forcing everyone else to sound shockingly quiet, and thereby forcing everyone else to double their loudness levels as well -- ending the improved dynamic range of HD once and for all. Anyway, if my instincts are correct about this headroom having been a way of helping mask the temporary bitrates' audible downside (one they knew the industry wouldn't be able to resist gobbling up forever), then I suppose this little postscript can serve as further evidence that the bitrates we hear on-air weren't meant to be around this long.