Emerging Radio Technologies -- On-air and Online

A Case Study in All-Digital HD AM Broadcasting: Refinements, Performance Tests, and Lessons Learned - $15

WWFD (820 kHz, Frederick MD), owned by Hubbard Radio and having engaged in a cooperative effort with Xperi Corporation to become the first AM broadcast station to transmit using the HD Radio MA3 mode full-time, commenced operations as such on July 16th, 2018. While initial performance met expectations in terms of coverage, a transmission problem occurred: the secondary and tertiary carriers, containing the stereo information and ancillary data services, were not being formed correctly and therefore suffering from excessive bit-error losses. Inadequate sampling of the baseband digital signal by the transmitter?s Pulse Duration Modulator (PDM) had led to excessive noise in the carriers and increased spectral regrowth in the transmitted RF signal. A second transmitter having a higher-phase PDM was installed, solving this issue. A further refinement was made by adding a phase rotation network to the day antenna, achieving Hermetian symmetry (already present on the night antenna), which presented a constant-conductance load to the transmitter. With the antenna system optimized, adaptive precorrection techniques were employed in the transmitter to minimize spectral regrowth, and improve signal robustness and receiver acquisition time. Day and night drive tests were conducted in the summer of 2019. Nighttime tests were repeated in the winter of 2019, to compare coverage with the reduced co-channel skywave interference conditions encountered earlier in the year.

With all-digital operation, the monitoring of licensed parameters must be revisited. Power measurement with regards to MA3 transmissions must be performed in a different manner than with standard analog AM transmissions, as pin-diode base current meters designed for AM do not accurately measure currents using the all-digital mode of operation. Procedures for performing power measurements with spectrum analyzers, power meters, and thermocouple RF ammeters are discussed.

Finally, some operational ?lessons learned? are presented. Techniques for optimal audio processing in conjunction with the high audio compression rate in the MA3 mode are discussed. A battery-protected power supply which keeps critical parts of the digital transmitter online during power interruptions was installed, thereby reducing system downtime during utility interruptions. It is hoped that the knowledge gained from WWFD?s experience will facilitate the conversion of other stations who are contemplating using the MA3 transmission mode.

Dave Kolesar | Hubbard Radio | Washington, DC USA
Mike Raide | Xperi Corporation | Columbia, MD USA

Audio-Specific Metadata To Enhance the Quality of Audio Streams and Podcasts - $15

Audio-specific metadata was envisioned several years ago in the MPEG-D standard for Dynamic Range Control. The application of this metadata to online content awaited a newer audio codec and the current generation of mobile operating systems. Now that both are becoming widely available, this paper explains how audio content providers can offer new consumer benefits as well as a more compelling listening experience.

This paper and presentation will explain the types of audio-specific metadata that monitor key characteristics of audio content, such as loudness, dynamic range and signal peaks. From simple to large-scale producers, the metadata sets are added to the content during encoding for real-time distribution?as in streams, or for file storage?as with podcasts.

In the playback device or system, this metadata is decoded along with the audio data frames. Through diagrams the decoder operations are described, providing benefits such as loudness matching across different audio content?ending annoying blasting from some audio and reaching for the volume. It will be shown that audio dynamic range can be controlled according to the noise environment around the listener?quiet parts of a performance can be raised to audibility, but only for those who need it.

An audio demonstration is planned to allow the audience to hear the same encoded program over a range of playout conditions with the same device, from riding public transit to full dynamic range for listeners who want highest fidelity. The workflows in production and distribution to add audio-specific metadata are explained, showing how content producers need to make only one target level for all listeners, rather than one for smart speakers, another for fidelity-conscious listeners, etc.

John Kean | Cavell Mertz & Associates Inc. | Manassas, Virginia, USA
Alex Kosiorek | Central Sound at Arizona PBS | Phoenix, Arizona, USA