The speaker says that some early speech-to-speech models, including Sesame, accepted speech input and produced speech output only.

“interpretability of such models like because you don't want it to be a black box so how can you understand where it is lacking and so that that's a lot of research that we do and how to make speech-to-speech models more interpretable the other constraint is I think initially the speech-to-speech models like I think sesame etc that came in that they were just speech-to-speech like they literally took in speech and gave out speech ours is like multi-model so”