Guess what? The sound quality of the new “HD Radio” system sucks! That’s the verdict of none other than the National Radio Systems Committee, the industry-sponsored group that develops radio broadcast standards in the U.S.
In an internal memo dated May 14 (.pdf, 94K), Milford Smith, chairman of the NRSC subcommittee on digital radio, announced it is “temporarily suspending its IBOC-DAB standards-setting process.” This is due in part to the results of recent on-air tests and a private demonstration held at the Washington, D.C. studios of National Public Radio. The evidence mostly involves the AM side of the iBiquity-engineered digital radio system.
Upon actually hearing the system work on the air, esteemed members of the DAB Subcommittee “do not consider the audio quality demonstrated by the iBiquity 36 kbps[!] PAC technology to be suitable for broadcast.” It seems that iBiquity originally demonstrated the IBOC system using a different, possibly non-proprietary audio encoding algorithm (codec). The “PAC” encoder being rolled out on IBOC-equipped radio stations around the country, however, is an in-house build, and of an inferior sound quality. One might call that a bait-and-switch….
The NRSC says there is a concern with IBOC-FM as well, due to the fact that “the poor performance of the PAC codec at low bit rates raises concerns of performance at intermediate rates.” The IBOC-FM system is designed to provide a 96 kbps-quality signal over the air, although the memo hints that the ending bit rate of most FM broadcasts will definitely be 64 kbps, as “ancillary data providers and secondary audio providers” want at least one-third of the bandwidth.
FM signals synthesized in the lab and tested on the air so far have been at the full 96 kbps – but if 64 becomes the default “sound,” NRSC wants to make sure that FM-IBOC won’t sound like sh*t, either.
This is a bump in the road because it does not raise any problems with how the digital radio signals are produced, just how the audio is encoded before transmission. Although there is evidence to suggest that the IBOC signal itself will cause interference problems on both the AM and FM bands, regardless of the codec used, this temporary pause in the standards-setting process has nothing to do with that problem.
Working out a problem that large would require redesigning from scratch, something iBiquity (and, by extension, the radio industry) is not willing to do, although at least one alternative AM digital radio system has recently been developed and awaits testing.
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