Sliding Time Scale/Pitch Shift Reducing Vocal Audio Quality

[SnoCone]

I'm using Windows 10 version 1607, Audacity 2.1.3, and used the .exe installer.

I was using the Sliding Time Scale/Pitch Shift tool to make a song gradually get about 10% faster. However, I noticed that whenever I used the tool, the sound quality for the vocals dropped significantly. I've included a small audio sample that has the original and then a 1% change on the tempo using the Sliding Time Scale/Pitch Shift tool. I found that the quality drop was persistent through different sizes of tempo changes (even 0%). I've also tried it on a few other tracks and noticed that it tended to affect vocal-heavy tracks the most, but not consistently.

Does anyone know why this could be happening or a way to avoid or fix it?

[steve]

I think it's just a limitation of the time-stretch algorithm, and that hearing tends to be extremely sensitive to quality changes in human voices (more so than other sounds).