Techy radio question

I'm asking here as I know there are some technically-minded posters on TVF so hope this topic is allowed.

On Radio 1 today, a round of the quiz on Scott Mills' show featured pan pipe covers of well-known pop songs. Listeners have to guess what song is being covered. The clips weren't great quality (slightly 'thin' sounding, if that's a thing). I was listening on headphones connected to my laptop streaming the BBC Sounds website.

It then became apparent that people listening on some radios couldn't hear the clips at all, with Scott concluding that the clips were 'out of phase'. It's a bit of a fun quiz, all quite-hearted - so they improvised by whistling for those who couldn't hear the clips.

Can anyone explain what actually happened though? You can hear on BBC Sounds here (from about 2:13:50). People start texting to complain during the second question.

I suspect what has happened is if you're listening on a mono radio, they didn't encode the track properly, so instead of getting the stereo track mixed down to mono, they got nothing or you'd need really good hearing to hear it. Even in stereo it sounds naff.

Ah. They do seem to just grab clips off the internet for this feature. Quite funny hearing the presenter explain the problem to the producer...

Next question, how many people are listening in mono these days? Seems significant to have quite a lot texting in! (Edit: any radio with a single speaker I guess).

Just listening to those clips on BBC Sounds with stereo speakers, it's pretty obvious that the first two are out of phase. Third one seemed fine (at least to my ears - don't have an AMU to hand).

Assuming it wasn't a bad import by someone in the production team, then it's likely whoever originally made it recorded the instrument mono, and then to give it a 'stereo effect' inverted one of the channels.

Perfectly audible when listening in stereo (albeit with some interesting spacial effects), but when mixed down to mono (either in transmission or by the listener's receiver) the two channels cancel each other out.

Proof:



The inversion of one channel gives your brain a hard time when it tries to work out where the sound is coming from (it uses timing differences as well as loudness to do so) so it can end up sounding like it's behind you or spread out all around you.

Sounds like those godawful Beatles compilations where they've split four mono tracks over two left and two right channels, where you end up with drums in one ear and vocals in the other.

Thanks for the explanation! I'll miss this place...

I've since found you can very easily switch Windows 10 audio to mono, and you're right - it's the first two clips that are affected.

Lots of smart speakers are in mono, for example.

No, it’s very different from that.

I know it's different from that, I said it "sounds" like them.

To my ears.

Subjectively.

This forum really is dying a death at the right time. Bloody nitpickers.

This whole thing of adding the two signals together and them cancelling each other out is how FM Stereo works, and how stereo was able to be added to the original mono signal without breaking existing mono radios.

Rather than transmitting a left and a right signal, what they actually do is transmit a mono signal (eg L+R) and a second channel which is the difference between them (L-R).

Stereo radios mix the two together. Mono + difference gives you the left channel, mono - difference gives you the right channel.

Mono radios ignore the difference signal and just use the mono channel. Which I think is genius.

Charming. I mean clearly almost two decades experience working in (audio and video) broadcast engineering just makes me a ‘bloody nitpicker’.

If out of phase audio sounds to you like a pop record from the early days of stereo mixing then I’d be concerned about your hearing. The two sound very very different.