Changing the TTS Backend

The text-to-speech (TTS) backend is the software that actually converts text to speech. The default backend is your system’s accessibility speech, which is simple, lightweight, and fast. However, it is not necessarily the most realistic or flexible TTS engine. There are several cloud services that provide TTS, such as Amazon Polly. PyLips currently supports Amazon Polly, but we plan to add other services in the future.

Integrating with Amazon Polly

To use Amazon Polly, you will need to set up the AWS CLI for your system. This Medium article does a great job of explaining the steps you will need to take. Be sure to allow Polly access; Polly has a free trial for one year that allows you to perform TTS with up to 5 million characters per month for free.

Once you have set up the AWS CLI, you can use it by passing ‘polly’ to the RobotFace constructor:

from pylips.speech import RobotFace

face = RobotFace(tts_method='polly')

You can also pass different voice_ids as in the “changing the voice” example. A description of the different voices for Polly are available here.

In addition, Amazon Polly has many options to customize the TTS output. Specifically, Polly uses SSML to customize the output. SSML is a markup language that allows you to control the pitch, rate, volume, and other aspects of the speech. You can directly pass SSML to the say method:

from pylips.speech import RobotFace

face = RobotFace(tts_method='polly')
face.say('<prosody rate="slow">Hello, world!</prosody>')