What is the Speech service (preview)?

The Speech service, part of Microsoft's Cognitive Services, unites several Azure speech services that were previously available separately: Bing Speech (comprising speech recognition and text to speech), Custom Speech, and Speech Translation. Like its precursors, the Speech service is powered by the technologies used in other Microsoft products, including Cortana and Microsoft Office.


The Speech service is currently in public preview. Return here regularly for updates to documentation, additional code samples, and more.

With one subscription, the unified Speech service gives developers an easy way to give their applications powerful speech-enabled features. Your apps can now feature voice command, transcription, dictation, speech synthesis, and translation.

Function Description
Speech to Text Converts continuous human speech to text that can be used as input to your application. Can integrate with the Language Understanding service (LUIS) to derive user intent from utterances.
Text to Speech Converts text to audio files of natural-sounding synthesized speech.
Speech Translation Provide translations of speech to other languages, with text or speech output.

Using the Speech service

The Speech service is made available in two ways. The SDK abstracts away the details of the network protocols. The REST API works with any programming language but does not offer all the functions offered by the SDK.

to Text
Text to

SDKs Yes No Yes Libraries for specific programming languages that simplify development.
REST Yes Yes No A simple HTTP-based API that makes it easy to add speech to your application.

Speech to Text

The Speech to Text (STT), or speech recognition, API transcribes audio streams into text that your application can accept as input. Your application can then, for example, enter the text into a document or act upon it as a command.

Speech to Text has been separately optimized for interactive, conversation, and dictation scenarios. The following are common use cases for the Speech to Text API.

  • Recognize a brief utterance, such as a command, without interim results
  • Transcribe a long, previously-recorded utterance, such as a voicemail message
  • Transcribe streaming speech in real-time, with partial results, for dictation
  • Determine what users want to do based on a spoken natural-language request

The Speech to Text API supports interactive speech transcription with real-time continuous recognition and interim results. It also supports end-of-speech detection, optional automatic capitalization and punctuation, profanity masking, and text normalization.

You can customize Speech to Text acoustic and language models to accommodate specialized vocabulary, noisy environments, and different ways of speaking.

Text to Speech

The Text to Speech (TTS), or speech synthesis, API converts plain text to natural-sounding speech, delivered to your application in an audio file. Multiple voices, varying in gender or accent, are available for many supported languages.

The API supports Speech Synthesis Markup Language (SSML) tags, so you can specify exact phonetic pronunciation for troublesome words. SSML can also indicate speech characteristics (including emphasis, rate, volume, gender, and pitch) right in the text.

The following are common use cases for the Text to Speech API.

  • Speech output as an alternative screen output for visually-impaired users
  • Voice prompting for in-car applications such as navigation
  • Conversational user interfaces in concert with the Speech to Text API

If you need an unsupported dialect or just want a unique voice for your application, the Text to Speech API supports custom voice models.

Speech Translation

The Speech Translation API can be used either to translate streaming audio in near-real-time or to process recorded speech. In streaming translation, the service returns interim results that can be displayed to the user to indicate translation progress. The results may be returned either as text or as voice.

Use cases for Speech Translation include the following.

  • Implement a "conversational" translation mobile app or device for travelers
  • Provide automatic translations for subtitling of audio and video recordings

Speech Devices SDK

With the introduction of the unified Speech service, Microsoft and its partners offer an integrated hardware/software platform optimized for developing speech-enabled devices: the Speech Devices SDK. This SDK is suitable for developing smart speech devices for all types of applications.

The Speech Devices SDK allows you to build your own ambient devices with a customized wake word, so that the cue that triggers audio capture is unique to your brand. It also provides superior audio processing from multi-channel sources for more accurate speech recognition, including noise suppression, far-field voice, and beamforming.

The SDK is based on web sockets using port 443.

Next steps

Get a free trial subscription key for the Speech service.