sonic

You can pass Espeak recordings around legally. It's just GPL. The license applies to the software, not the content produced via it. I will attempt to remember and find the time to take my demo recording of this on Rust compiler source code that's currently in dropbox and put it up somewhere more permanent. I doubt Dropbox will care for me much if I allow HN-volume traffic to hit my account. It's Espeak using an NVDA fork with an additional voice that some of us like, so vanilla espeak is in the ballpark. What I don't remember is if vanilla non-libsonic espeak softcaps the speech rate. It might. I believe new versions of espeak integrate libsonic directly, but that old versions just silently bump the speaking rate down if it's over the max. I haven't used command line espeak directly for anything in a very long time. Libsonic is an op

Yes the speech rate algorithm is important. The application I use uses the Sonic algorithm by Bill Cox, which is actually optimized for rates over 2x. https://github.com/waywardgeek/sonic I think speed rate should be a standard control on every multimedia player, just like volume.

For me the best sound speed up I've found is the Android app "Presto" that can be used by the Podcast app as a speedup service. It uses the Sonic algorithm which is specifically tailored for speech speedups above 2x. https://github.com/waywardgeek/sonic