negative pitch values fail using gcp mode using -2.0 works fine with +2.0 about tts HOT 1 CLOSED

Oh yes, I ran into this too but forgot to mention it in the docs. The problem is in how the CLI parser interprets arguments that begin with a hyphen. The workaround is to use the alternate "equal sign" format for those arguments: tts test.txt test.mp3 --service gcp --project-file xxxx.json --language en-uS --type ssml --voice en-US-Wavenet-B --pitch=-2.0 (note the = between the pitch name and value).

I might be able to tweak the code so that the equal-sign format is not necessary. At the very least I'll add a note to the docs to point that out.

More technical explanation:
The parser module follows POSIX conventions, so anything that begins with a hyphen is considered an option. So something like --pitch -2 is interpreted as 2 different options, pitch=true and 2=true (nevermind that seems nonsensical), rather than pitch=2.

from tts.