Over the years quite a few of our listeners have asked us to do broadcasts using the DRM system. We don’t ever plan on using DRM to broadcast RNEI and thought we’d make this page to explain our reasoning:
- Receiver Compatibility: DRM signals typically require the use of expensive and scarcely available physical radios, a wide SSB radio and a PC or the use of an SDR to decode them. The SDR & PC options require compatible software e.g. DREAM. DRM software has it’s own issues:
- Codec Licencing (It’s not free or legal for everyone to receive): DRM uses the AAC, AAC+ & xHE-AAC codecs. These are not free codecs and require proper licencing to be legal. DREAM on Windows is usually workable with AAC (e.g. used by RRI) after downloading a dll of questionable legality.
Higher-quality xHE-AAC broadcasts over DRM only have a few somewhat complex options to decode on a PC / SDR. KiwiSDRs support xHE-AAC natively but we’re not a show broadcasting only to KiwiSDR users!
- Dropouts are (on most days) Inevitable: We use HF / Shortwave. This medium is full of challenges like multipath, signal strength fluctuation, doppler and more. While DRM does a fantastic job coping with these difficult conditions, over a 1 hour long show having some dropouts is almost guaranteed on all put a perfect propagation day. Dropouts interrupt speech and music and we don’t think it’d be a good experience for listeners of our show.
- Interference / RFI / A neighbouring station can ruin any chance to decode: DRM doesn’t cope well with co-channel interference, a neighbouring signal or RFI whereas an AM radio will present you with some form of the show with the interference clearly present. We feel hearing something is better than nothing.
- DXing: We love our DXers and dedicated listeners who listen despite the poor signal. DRM has a minimum signal strength to decode whereas AM does not. If you have any audio data present in an AM signal, you will hear it. This makes for a much better weak signal / DXing experience.
- Bitrates: [to add]
- SDR software in 2023 can fix most issues of AM radio: In 2023 there are now options for:
- AM-Sync / DSB / SAM which will remove most issues related to carrier fading (the exploitive distortion issue).
- Noise removal (especially in SDR#) which can reduce if not remove noise and below-signal-level RFI to bring the audio quality to levels that are really good, possibly better than some DRM modes.
- Anti-Fading systems to further reduce issues related to multipath and enhance audio clarity.
- The CombStereo system to decode a stereo track from any recording of our AM signal.
- Auto-EQ systems to fix fading related “EQ” changes.
With options of using modern SDR software & CombStereo, we feel the need to use DRM to get high quality audio over HF might have passed, especially if portable radios are released in future with the technical improvements seen in SDR software.
We hope this explains why we don’t investigate broadcasting in DRM modes.