TTS Streaming - Cognigy Documentation

TTS Streaming Feature

The TTS Streaming feature delivers synthesized speech to your voice AI Agent as it’s generated, rather than waiting for the entire response to finish processing. This feature enables faster, more natural-sounding conversations. Standard TTS systems wait for the entire text to be processed before playing any audio, which introduces a noticeable delay, especially with longer texts. TTS streaming instead processes text in segments and plays each one back as soon as it’s synthesized.

Some speech providers use streaming to describe their API’s connection method, for example, a websocket-based API for submitting multiple texts. This concept is different from TTS streaming in Voice Gateway, which refers to audio playout: how quickly synthesized audio starts playing back to the caller.

Key Benefits

• Lower response latency. Audio playback starts as soon as the first words are synthesized, instead of after the full text is processed.
• More natural conversation flow. Reduced time-to-first-audio makes voice AI Agent responses feel closer to real-time human conversation, especially with longer text.

Prerequisites

• A voice AI Agent configured.
• A speech service configured in the Voice Gateway Self-Service Portal.

Restrictions

• The following speech providers don’t support TTS Streaming: AWS, Google, Nuance, Speechmatics, and Deepgram Flux.
• TTS vendor fallback doesn’t work with TTS Streaming. If TTS streaming is activated, the fallback vendor configuration is ignored.
• For ElevenLabs, Voice Gateway uses the ElevenLabs streaming API. The following parameters aren’t supported and can’t be specified in Extra Options:
  • seed
  • previous_request_ids
  • next_request_ids
  • apply_text_normalization
  • apply_language_text_normalization
  • use_pvc_as_ivc
  • pronunciation_dictionary_locators

How to Configure TTS Streaming

To activate streaming for your voice AI Agent, follow these steps:

1. Configure Speech Service in Voice Gateway Self-Service Portal.

   1. In the navigation menu of the Voice Gateway Self-Service Portal, select Speech.
   2. On the Speech services page, select an existing speech service or create a new one by clicking Add a speech service in the upper-right corner.
   3. On the Add Speech service page, make sure that the Use for text-to-speech option is activated.
   4. Activate the Enable text-to-speech streaming option.
   5. (Optional) For ElevenLabs, configure the Extra Options field to customize the TTS streaming behavior. See the list of unsupported parameters in the Restrictions section.
   6. Click Save.

2. Configure the Set Session Config Node in Cognigy.AI.

   1. Go to the Set Session Config Node in your Flow.
   2. In the Synthesizer (TTS) section, select your speech service from the TTS Vendor list.
   3. Configure TTS Language and TTS Voice as needed.

More Information

• Speech Services
• TTS and STT vendors

Last modified on July 8, 2026.