It may be that you've ended up resampling it.

That sounds like a reasonable explanation to the effect I was hearing.

Does anyone know at what sample rate RA is encoded, or how to determine it, if it has multiple sample rates?

Yeah, in messing around with RealPlayer, I was unable to see any detailed data on the track format that it was playing.

but I was just testing the CarTalk, and not looking for remarkably high fidelity.

Me too, but in going back and forth with a simple A/B between the source RA file and the generated WAV file, it was a pretty obvious problem.

And if the real-time decoding thing is actually true, then it's time to start shopping for a different RA-to-MP3 converter program. If I want to batch-encode CarTalk episodes, I don't want to have to wait an hour for each one.