As part of the packet loss challenge, there was an ASR word accuracy evaluation to see how PLC impacted intelligibility. See https://www.microsoft.com/en-us/research/academic-program/au...

The good news is that we were able to improve intelligibility slightly compared with filling with zeros (it's also a lot less annoying to listen to). The bad news is that you can only do so much with PLC, which is why we then pursued the Deep Redundancy (DRED) idea.

Right, this is why the Proper radio calls for a lot of systems have mandatory read back steps, so that we're sure two humans have achieved a shared understanding regardless of how sure they are of what they heard. It not only matters whether you heard correctly, it also matters whether you understood correctly.

e.g. train driver asks for an "Up Fast" block. His train is sat on Down Fast, the Up Fast is adjacent, so then he can walk on the (now safe) railway track and inspect his train at track level, which is exactly what he, knowing the fault he's investigating, was taught to do.

Signaller hears "Up Fast" but thinks duh, stupid train driver forgot he's on Down Fast. He doesn't need a block, the signalling system knows the train is in the way and won't let the signaller route trains on that section. So the Up Fast line isn't made safe.

If they leave the call here, both think they've achieved understanding but actually there is no shared understanding and that's a safety critical mistake.

If they follow a read-back procedure they discover the mistake. "So I have my Up Fast block?" "You're stopped on Down Fast, you don't need an Up Fast block". "I know that, I need Up Fast. I want to walk along the track!" "Oh! I see now, I am filling out the paperwork for you to take Up Fast". Both humans now understand what's going on correctly.