The author is chief engineer and IT manager of Portland Radio Group.
I agree with everything Glynn Walden explained in his article “Mono on FM: Hang on a Moment.”
In-car listening has been greatly improved over the years, with DSP and other techniques to improve the listening experience, and operating in mono is not a huge improvement for many situations.
I’m a big proponent of mono transmission for low-power stations or spoken word. It makes a huge difference in non-mobile receiving environments.
Office and home audio systems, portable radios and the like have their limitations. I’ve observed that listening to lower-powered stations (or full-power stations outside the 70 dBu contour) in residential and commercial environments can be a noisy experience; the receiver could be decoding full stereo even with noise –20 dB below the decoded audio. Many radios have automatic switching with no manual override for mono, and there are other situations where the user is unaware of the improvement mono can provide.
Those who have chosen to broadcast in mono likely have many experiences where they felt powerless about local noise, so they made the conscious decision to force the issue and provide the best experience possible for the greatest number of listeners by using mono.
So far, with three music translators, I’ve received only one call about not broadcasting in stereo. I’ve also found that many radios don’t even have a stereo light, so who’s to know which mode the station is in?
One compromise: The Omnia 9 audio processor, a wonderful toolbox of audio innovation, has a feature that is useful for just this situation, called Auto Pilot. This feature detects speech and low L–R to automatically switch off the pilot. I see this as a reasonable option for those who want music in stereo (which will mask the noise) and speech in mono.