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HD Listening Tests

D

diymedia

Guest
Question: have any listening tests ever been done of HDC? I'm thinking of the sort where a general and expert listener population grade the codec's performance relative to analog, in both clear and impaired listening situations.
 
diymedia said:
Question: have any listening tests ever been done of HDC? I'm thinking of the sort where a general and expert listener population grade the codec's performance relative to analog, in both clear and impaired listening situations.
Click to expand...

No.

HDC was announced by press release on August 12, 2003. https://ibiquity.com/press/pr/081203.htm It was adopted based on the opinion of the radio industry engineers who heard it, in comparison to PAC (which, up to that point, was the tested and FCC-approved codec for IBOC).

In the very early days there were listening tests conducted on both AAC (proposed by USADR) and PAC (proposed by LDR, later iBiquity). However, as I remember it, this was before the idea emerged to create supplementary channels. The testing was done on the full data rate configurations (for both AM and FM).

- Jonathan
 
diymedia said:
Question: have any listening tests ever been done of HDC? I'm thinking of the sort where a general and expert listener population grade the codec's performance relative to analog, in both clear and impaired listening situations.
Click to expand...

Listening tests conducted by the HD cartel were fatally flawed, because they were not conducted scientifically, there was no double blind comparison, they are not repeatable, and were not submitted for peer and public review.

I conducted my own set of tests - as impartially as I could (remember that I am motivated to use the system because it is the only place my preferred formats are offered over the air).

My worst fears about the shortcomings of the system have not only been confirmed, but exceeded for HD-AM. The slightest bit of background noise causes the system to drop out, other than that I have confirmed about 80 miles on a 10 kW station. Other testers have documented 150 miles, but I have yet to confirm such a feat due to the lack of clear channel 50kW clears in the area running HD. I have never received HD at night on any station - too much interference from adjacents and co-channels. Before and after comparisons of C-Quam and HD show a 330 mile range for C-Quam daytime, vs. 30 mile for HD on one station. On another, it was 290 miles for C-Quam and less than 10 miles for HD after the conversion.

The only finding I have that is encouraging is how far HD FM really goes. On stations that have not implemented the ill-advised sideband power increase, I have documented over 60 miles in the car, with no range limit yet. I have done 65 miles with a dipole on a home tuner, with another observer getting 84 mile reception with a dipole. With an outdoor antenna, the range is close to 250 miles, provided there are no first adjacents anywhere nearby, nor any skip from a co-channel. The HD-2 subchannels are a good idea, but the recovery time from a dropout is unacceptable for consumer audio, whose users are not used to the warm up times of old tube equipment.

Both AM and FM HD have the unfortunate side effect of reducing the station's analog coverage, sometimes drastically. My theory is that the problem is on the receive end, with the receiver AGC confused by the presence of the sideband. I was fortunate to find a station that implemented and dropped HD a couple of times. Drive tests showed their range to be 150 miles without HD, and less than 90 miles analog coverage with HD. This has severe implications for local building penetration. Similar decreases in range occurred on virtually all stations in both Dallas and Ft. Worth, with ranges that had previously been 150 miles or even more reduced to about 90 miles. AM experiences similar decreases in range, with even more severe consequences for local building penetration.

I conducted these tests as scientifically as I could. No double blind testing was possible, but the results were repeatable on different occasions, different times of year, and multiple stations with multiple receivers. All receivers were aligned prior to testing and in good condition.
 
Thanks for this! The only testing in the record that I can find of this kind is from Lucent Digital Radio, filed in RM-9395 on January 24, 2000, and involves evaluation of PAC on FM only.
 
Another drive test. Test station - KGLK Lake Jackson, TX. Pioneer DEH-P9400BH receiver, 31 inch whip antenna. HD reception dropped out for 30 seconds just past the highway 362 interchange on highway 290, a distance of 68.7 miles.
 
diymedia said:
The only testing in the record that I can find of this kind is from Lucent Digital Radio, filed in RM-9395 on January 24, 2000, and involves evaluation of PAC on FM only.
Click to expand...

Paragraph 18 of the First Report and Order http://transition.fcc.gov/fcc-bin/audio/FCC-02-286A1.pdf summarizes the state of codec testing at the time (October 10, 2002). The testing report referenced in footnote 29 is found at http://apps.fcc.gov/ecfs/comment/view?id=5508336350 (two documents).

To the best of knowledge, no formal test report of PAC on the AM system was ever published (if, in fact, a formal test had been done). However, there were contemporaneous stories at the time about its shortcomings. See, e.g., http://www.radioworld.com/article/ibiquity-charts-a-new-course/16245

- Jonathan
 
IIRC, the original codec for HD-AM was absolutely horrible when shown at either CES or NAB such that the horrified engineers insisted iBiquity trash it, so they went back to the drawing board and came up with the AM-HD current codec that works okay with music, but is for sh** with cellphone calls and bassy talk show hosts (and any day with a thunderstorm within 100 miles).
 
Interesting. So the only subjective, comparative listening data in the public record is really that from Lucent circa 2000. Thanks to all!
 
There's actually 3 listed in the NRSC standards:

http://www.nrscstandards.org/Reports.asp

Look for "Generation 1, 2, and 3". It's not perfect, because the digital evaluation is at 96 kilobits, which almost nobody actually uses. It also has the processing switched off for the HD test and on for the FM test. Hardly fair, and also not representative of what is actually being used.

Dave B.
 
Interesting. Wonder if there's a way to get hold of Ellyn Sheffield's report(s) to learn more about how the tests were conducted (sample size, etc.).
 
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