AM station operators considering or currently on the air with AM IBOC digital signals now have a more analog-friendly signal option. Ibiquity's new modified MA1 specification, introduced by Jeff Detweiler at a radio technology engineering session at the 2010 NAB Show, allows broadcasters to sacrifice a degree of digital throughput in exchange for a somewhat higher analog bandwidth and a commensurate noise-floor reduction in analog receivers.
Specifically, the new specification allows for operation in a "core only" mode, eliminating the tertiary and secondary digital carriers that lie closer to the carrier with the analog sidebands. This permits the use of broader analog audio filtering by the broadcaster for improved analog quality and also reduces so-called "self interference" that manifests itself as a higher analog noise floor.
While IBOC audio data throughput using the modified scheme is reduced from 36kb/s to 20kb/s, improved low-bit-rate codecs employing spectral replication permit higher quality digital audio than was available using previous codec options.
Ibiquity hopes the new option may convince some AM broadcasters previously squeamish about sacrificing analog reception quality with their current audience to reconsider IBOC digital conversion.