I was watching the ep on YouTube, and I tend to have headphones because my laptop's speakers aren't too good, so that's how I caught it. Even when YouTube compresses the heck out of the sound, you can still make out details.
The sound mix is also one of the things I love about the series. In scenes where the characters are outside and talking, the acoustics are adjusted in such a way that they actually do sound like they're outdoors (voices echoing off buildings, etc). Most other cartoons don't even bother with such details.