I've always found this interesting. Think+transmit seems more likely to be the bottleneck vs receive, given that we can easily parse most podcasts etc at 3-4X speed. If being understood by everyone wasn't required, I wonder if one could learn to boost both send and receive rates?

I usually listen at 1.5x passively.

But what you said made me curious. I listened to this podcast at 3x. I was able to understand all the words, but my conceptual understanding decreased. I also have to listen actively -- not passively.

https://www.youtube.com/watch?v=9SFkwdm0PP0

At 4x, I could only understand the shape of the sentences but could no longer make out the words. But I turned on the captions and found I could keep up. Turns out reading at 4x works, listening at 4x doesn't.

English is also spoken with different prosodies and cadences. For instance, I can understand Singaporean English perfectly, but it's less amenable to being sped up. I tried listening to this lecture in Singaporean English in 3x and found that I could barely understand it.

https://www.youtube.com/watch?v=LA1dnUYzRWU

This suggest that maybe human minds are able to form ideas at a certain speed, and language has evolved to convey these ideas and not be a bottleneck, but there is no reason to improve language beyond this.

Likely so. I've noticed that those whose first language is one of those with fewer vowels - and thus must have more syllables per second to convey the same information rate- sometimes speak English much faster than I (as a monolingual native speaker) find normal.

3-4x! Are you the flash? I usually run things about 1.5x when I am commuting. 3x would require laser focus without distractions. Or you mean more a “can technically absorb the language being spoken” sense?