I don't know if this built in one is any better these days:


Generate Synthetic Vocal - Sinsy

You can hear Band-in-a-Box singing, with built-in support for the popular online vocal synth "Sinsy."

To access this feature, you should first enter melodies and lyrics to the Melody or Soloist track. If no lyrics are present, you can still generate a vocal synth using the syllable of your choice (e.g. la la la).

You can launch the Vocal Synth generation by one of the followings.

- Press the [Vocal Synth] button on the Notation window toolbar and select either of the Vocal Synth (auto or manual) menu items.

- Press the [Big Lyrics] tool bar button, and select either of the Vocal Synth (auto or manual) menu items.

- Go to menu Edit - Lyrics - Vocal Synth.

With the manual mode, Band-in-a-Box creates a Sound.XML file, which you need to upload to the Sinsy server. When the Sinsy has generated an audio file with a vocal synth, import it to Band-in-a-Box.
https://www-sinsy-jp