Bilingual speakers sometimes change their pitch and voice quality when they switch from one language to the other. For example, when speaking in L2 rather than L1, German learners of French pronounce vowels with less adduction of the vocal folds (Pützer et al., 2016), and Korean learners of English with a lower pitch (Cheng, 2020). Here, I present a corpus study which suggests that the extent to which L2 learners of English change their pitch and voice quality may depend on how similar their L1 is to English. I extracted 68 211 vowels—51 857 in L1 and 16 354 in L2—from 1617 speakers with 21 different L1 backgrounds (including English) in the CSLU: 22 Languages Corpus and measured F0, harmonics-to-noise ratio (HNR), and H1i–H2 for each vowel. I then computed two cluster distances for each L1 and for each measure: (1) vowels from the native English speakers versus L1 vowels from the learners and (2) L1 vowels versus L2 vowels from the learners. I found strong correlations between (1) and (2): r = 0.416 for F0 (p = 0.068), r = 0.531 for HNR (p = 0.016), and r = 0.374 for H1–H2 (p = 0.105).