This is one in a series in which Ibiquity Digital Corp. answers questions about how to implement HD Radio, the newly-trademarked name of what used to be called in-band, on-channel digital audio broadcasting. Broadcast Technology Manager Jeff Detweiler answers here.
Q: I am reviewing an SCA performance contract with a prospective broadcast tenant. How will my plans to implement IBOC impact my SCA operations?
A: IBOC implementation should not impact your SCA business. However, we believe that over time, most of these services desire to migrate to the more robust digital signal available as a standard capability in new receivers.
Tests on SCA compatibility verify that the hybrid mode (in which the analog and digital signals are both transmitted) of Ibiquity’s HD Radio IBOC system has no significant impact on SCA performance.
Appendix J of the NRSC’s FM “IBOC Evaluation Report” available on the NRSC Web site at: www.nab.org/SciTech/nrsc.asp, concludes that “the perceptual scores indicate that the overall utility of the subcarrier is not particularly diminished with the addition of FM IBOC signals, because the field test subjective scores remain well above the listener ‘tune-out’ threshold” identified in an Ibiquity Digital report.
To further support this conclusion, Ibiquity Digital’s report “Experimental Report on (IBOC) DAB Compatibility with Existing SCAs” confirms that the audio signal-to-noise ratio of recovered audio from the 67 kHz SCA observed with baseline IBOC carriers (-20dB host), while receiver dependent, was not impaired enough to cause interference with, or impact to, the host SCAs range of reception.
SCAs located at 92 kHz are more prone to noise and interference, as the noise floor and the IBOC intermodulation products are higher at upper baseband frequencies. Even in this interference prone spectrum, 92 kHz SCA audio had SNR reduction of only 2 dB.
The test results for digital modulated SCA channels show that IBOC degradation was in the 0.5 percent range. This test result translates to less than one-tenth of a dB on the bit error rate curve, which would result in a negligible impact on a digital SCA’s service area.
Additional support can be found a study by National Public Radio and the International Association for Audio Information Services, “Further Report on Analog SCA Compatibility with Ibiquity Digital’s FM-IBOC System.” This report also is available on the NRSC Web site. The report states, “On average, the added IBOC-interference effect, based on population, was projected at 2.6 percent.”
The benefits offered by the audio quality and advanced data services of the HD Radio system clearly outweigh any potential impact on analog SCA services. Both can easily coexist on the host station during the hybrid phase of implementation.
Send your IBOC questions to firstname.lastname@example.org. Radio World welcomes other points of view.