I use VLC for a random assortment of video and audio files (podcasts, etc--mostly people talking), so I can't really narrow this to any particular kinds of encoding or whatever else beyond saying that they're mainly mp4's and mp3's, but I'm wondering if any of the many audio settings in VLC pertain to making the audio sound better, or at least different, when it's sped up (typically 1.1 to 1.5).
At least half the time media sounds fine sped up, but the rest of the time the audio sounds slightly distorted sped up, lacking the smoothness that it would have at 1.0. This isn't a function of how high it's set, either, since it's just as likely to happen at 1.1 as anything higher. Some files just don't seem to work well sped up for whatever reason.
Sometimes I'll open them up in MPC-HC to see how they sound there, and often they sound fine at the equivalent higher speed. I've noticed this especially with MP3s. This leads me to believe that there might well be a setting.
I use Win10 and have 2.24, but I've noticed this over many versions.