Voice is only available through the Oracle Android, iOS and Web SDKs, which work with instances of Oracle Digital Assistant that were provisioned on Oracle Cloud Infrastructure (sometimes referred to as the Generation 2 cloud infrastructure). You cannot use these SDKs (and therefore cannot integrate voice) if your instance is provisioned on the Oracle Cloud Platform (as are all version 19.4.1 instances).
When speech recognition is enabled, a microphone button replaces the send button whenever the user input field is empty. Users tap this button to begin recording their voices. The speech is sent to the speech server for recognition, converted to text, and then sent to the skill. If the speech is only partly recognized, then the partial result is displayed in the user input field, allowing the user to clean it up before sending it to the skill