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Comment by subhro | Hacker News Reader

As a pilot and a radio officer, I have always been able to process and service 2 audio streams simultaneously. So not surprised with this finding.

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I've always been impressed by the controllers in centers and TRACONs. They can have multiple frequencies they're monitoring in each ear, and no matter how polite we try to be we (pilots) have no way of knowing if we're stepping on a call on another frequency. They just have to deal with it. Not to mention communication amongst themselves to some extent as they hand people off, though I haven't been in a tower for a very long time, that may be automated/digital now.

And it's not like pilot/controller conversations are about weekend BBQ plans. It's as information dense as possible without sounding like a METAR report.

The drive through window staffers at restaurants do this, and it’s crazy. They will tell me my order and total, accept payment, and send me to the next window, all while listening to the next person tell them their order.

That tracks. As a teacher I sometimes find myself conversing with multiple kids simultaniously as well. If it's nothing too deep that requires full focus, it works. (Though I do find it tiring and avoid it.)

Perhaps a dumb question but are they center panned (or mono, i.e. talking over each other) or is it split left ear/right ear when they come through the headset?

Airplane radios are generally broadcasting and receiving mono. There are modern headsets that can also play stereo, but only for onboard music or intercom purposes, if the plane supports it. But in planes with 2 radios you can usually configure their I/O individually. So you can listen (and also talk, although that makes sense less often) on two frequencies at the same time.

Yes of course, the transmitted audio would be mono. I meant one radio in one ear and another radio in the other ear, or if you mix them and they both play in both ears. But it sounds like they're mixed (talking over each other in a single audio stream).

Yes. I have never seen any system (planes or elsewhere) that splits multiple voice communication inputs so you hear different streams in different ears. How would that be different (let alone better) than having both streams in both ears? It's not like your brain can process each ear separately.

But of course your brain can process each ear separately. You have a holistic conscious experience, but that is like a hallucination constructed by your brain for your own benefit. The raw signals are indeed "in stereo"

There are generally 4 ways you can deal with presenting two independent mono sources to one person using headphones:

1. Mix them together into one mono channel and send that to both ears.

2. One in each ear.

3. Make separate mixes for each ear. For each ear's mix make one of the sources louder than the other, picking a different source to make louder for each ear.

4. Like #3, but also add delay in each ear's mix to the source that is weaker in that ear.

#2 is generally better than #1. Personally I'd find it annoying because it is very unnatural, but it makes it a lot easier for the brain to separate the sources, makes it easier to focus on one and ignore the other if you need to do that, and prevents the auditory masking you can get when two sources are in same place in your perceived audio space.

#3 fixes the masking problem with #1 but #2 still because it is still easier to focus when you need to. Also, in each ear the weaker signal is unnatural and the brain expends some effort to filter it out, which is fatiguing over long periods.

#4 is by far the best. It solves the long term fatigue problem from #3 because our auditory system is built to expect a weaker version of anything one ear hears first to arrive shortly later at the other ear, and automatically filters it out instead of having to do it at a higher level. The delay shifts the perceived source of each voice to somewhere outside the head instead of somewhere inside, which is more natural, which is much less fatiguing than the "one voice" per ear approach (the brain almost always does more work when something seems unnatural).

Many military planes use #4, as do some Airbus models.

Different voice inputs in different ears wouldn't help since our brain processes auditory input on left/right side of brain based on the type of input, not which ear it came from. Speech is processed on the left side, and non-speech (music etc) on the right side.

> It's not like your brain can process each ear separately.

If you've ever seen a dance music DJ (Tomorrowland is streaming on Youtube right now!) - that's exactly what many of them do.

To DJ a continuous mix as is the norm for this style - generally you'll have headphones on, but only covering one ear. You'll listen to "currently playing" though your right ear, through the venue sound system (well, it's monitors). You'll also be listening to "up next", on the other record/cd/mp3 deck, through the headphones to your other ear. And you'll work the pitch slider, trim controls etc and hopefully produce a good mix!

Not everyone does it like this, some have the headphones permanently on and mix in stereo both tracks at both ears. Or split ears, headphones only - that is an option on the usual Pioneer mixers. But it's surely the most common mental image of a club DJ to have them holding their hand to their headphones on one ear only, I'm sure!

> I have never seen any system (planes or elsewhere) that splits multiple voice communication inputs so you hear different streams in different ears.

PS Engineering PMA450B is one, but most GA aircraft I’ve flown work like this.

> How would that be different

It would be different based on the fact you’d hear one conversation in your left ear, and another in your right ear.

> (let alone better)

Beauty is in the ear of the beholder.

> It's not like your brain can process each ear separately.

Different brains function differently.

Thanks, this was the info I was originally after :)

They are mono, but I was trying to say that with practice, you can process 2 independent audio streams simultaneously irrespective of whether they are mono or stereo. For example, I am able to keep track of 2 people talking at the same time. I obviously can't respond to both but can maintain independent contexts.

I wonder if piano players find that easier too, compared to lay people.

I think it was wondered whether you were having the independent streams panned hard to the left and right ears and if that had something to do with hemispheres of the brain and the processing efficiency.

That’s a super interesting question. I don’t think I isolate one stream to each ear since I can process them through headphones as well. Also routinely when I am working as a radio officer, I have conversations with live humans in the room while listening and responding to audio over RF through the headphone.

To be honest, I can’t articulate how I do it. I just somehow manage to do it.

I do it too, but I "buffer" one person's speech while I process the other's, and vice versa. Do you process both at once?

I wonder if reading techniques (i.e. human TTS) are also a bit like this. You have to "read ahead" and maintain a mental buffer, in order to parse the sentences so that you can put emphasis in the correct places, timing etc. So the eyes and mind are ahead of the speech.

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