Can you use pre-recorded audio to respond to voice calls using the Sinch platform?

Yes, you can use pre-recorded audio in multiple formats, including WAV and MP3.

Pre-recorded messages can be used on a IVR scenario, when you want to play messages in a menu scenario instead of using TTS, and it can also be used on a callout scenario, when the customer want to trigger a call to a destination number, and play a message directly, such as a PIN code for a OTP (One Time Password) call. 

Further Resources

• External media support – Content caching, limits, supported Content-Type headers.
• Text-to-speech Callout - Server initiates a call to a phone number and plays a synthesized text messages or pre-recorded sound files. 
• Playfiles - Plays Interactive Voice Response (IVR) files for the supported locale at the Sinch backend. An IVR message is played only on the caller’s side.