> ## Documentation Index > Fetch the complete documentation index at: https://docs.ultravox.ai/llms.txt > Use this file to discover all available pages before exploring further. # Preview Voice > Performs a test generation of a voice, returning the resulting audio or error. ## OpenAPI ````yaml post /api/voice_preview openapi: 3.0.3 info: title: Ultravox version: 0.1.0 description: API for the Ultravox service. servers: - url: https://api.ultravox.ai security: [] paths: /api/voice_preview: post: tags: - voices description: >- Performs a test generation of a voice, returning the resulting audio or error. operationId: preview_voice requestBody: content: application/json: schema: $ref: '#/components/schemas/Voice' required: true responses: '200': content: audio/wav: schema: type: string format: binary description: '' '400': content: application/json: schema: type: object additionalProperties: {} description: '' security: - apiKeyAuth: [] components: schemas: Voice: type: object properties: voiceId: type: string format: uuid readOnly: true name: type: string maxLength: 40 description: type: string nullable: true maxLength: 240 primaryLanguage: type: string nullable: true description: >- BCP47 language code for the primary language supported by this voice. maxLength: 10 languageLabel: type: string nullable: true readOnly: true description: >- Human-readable language label with flag emoji and English name (e.g., '🇺🇸 English (United States)'). previewUrl: format: uri type: string readOnly: true ownership: allOf: - $ref: '#/components/schemas/OwnershipEnum' readOnly: true billingStyle: allOf: - $ref: '#/components/schemas/BillingStyleEnum' readOnly: true description: >- How billing works for this voice. VOICE_BILLING_STYLE_INCLUDED - The cost of this voice is included in the call cost. There are no additional charges for it. VOICE_BILLING_STYLE_EXTERNAL - This voice requires an API key for its provider, who will bill for usage separately. provider: type: string readOnly: true nullable: true definition: $ref: '#/components/schemas/ultravox.v1.ExternalVoice' required: - billingStyle - definition - languageLabel - name - ownership - previewUrl - provider - voiceId OwnershipEnum: enum: - public - private type: string BillingStyleEnum: enum: - VOICE_BILLING_STYLE_INCLUDED - VOICE_BILLING_STYLE_EXTERNAL type: string ultravox.v1.ExternalVoice: type: object properties: elevenLabs: allOf: - $ref: '#/components/schemas/ultravox.v1.ElevenLabsVoice' description: A voice served by ElevenLabs. cartesia: allOf: - $ref: '#/components/schemas/ultravox.v1.CartesiaVoice' description: A voice served by Cartesia. lmnt: allOf: - $ref: '#/components/schemas/ultravox.v1.LmntVoice' description: A voice served by LMNT. google: allOf: - $ref: '#/components/schemas/ultravox.v1.GoogleVoice' description: |- A voice served by Google, using bidirectional streaming. (For non-streaming or output-only streaming, use generic.) inworld: allOf: - $ref: '#/components/schemas/ultravox.v1.InworldVoice' description: |- A voice served by Inworld, using bidirectional streaming. (For non-streaming or output-only streaming, use generic.) respeecher: allOf: - $ref: '#/components/schemas/ultravox.v1.RespeecherVoice' description: A voice served by Respeecher, using bidirectional streaming. generic: allOf: - $ref: '#/components/schemas/ultravox.v1.GenericVoice' description: A voice served by a generic REST-based TTS API. description: >- A voice not known to Ultravox Realtime that can nonetheless be used for a call. Such voices are significantly less validated than normal voices and you'll be responsible for your own TTS-related errors. Exactly one field must be set. ultravox.v1.ElevenLabsVoice: type: object properties: voiceId: type: string description: The ID of the voice in ElevenLabs. model: type: string description: The ElevenLabs model to use. speed: type: number description: |- The speaking rate. Must be between 0.7 and 1.2. Defaults to 1. See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.body.voice_settings.speed format: float useSpeakerBoost: type: boolean description: >- See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.body.voice_settings.use_speaker_boost style: type: number description: >- See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.body.voice_settings.style format: float similarityBoost: type: number description: >- See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.body.voice_settings.similarity_boost format: float stability: type: number description: >- See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.body.voice_settings.stability format: float pronunciationDictionaries: type: array items: $ref: >- #/components/schemas/ultravox.v1.ElevenLabsVoice_PronunciationDictionaryReference description: >- See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.body.pronunciation_dictionary_locators optimizeStreamingLatency: type: integer description: >- See https://elevenlabs.io/docs/api-reference/text-to-speech/convert#request.query.optimize_streaming_latency.optimize_streaming_latency format: int32 maxSampleRate: type: integer description: >- The maximum sample rate Ultravox will try to use. ElevenLabs limits your allowed sample rate based on your tier. See https://elevenlabs.io/pricing#pricing-table (and click "Show API details") format: int32 description: Specification for a voice served by ElevenLabs. ultravox.v1.CartesiaVoice: type: object properties: voiceId: type: string description: The ID of the voice in Cartesia. model: type: string description: The Cartesia model to use. speed: type: number description: >- (Deprecated) The speaking rate. Must be between -1 and 1. Defaults to 0. format: float emotion: type: string description: (Deprecated) Use generation_config.emotion instead. emotions: type: array items: type: string description: (Deprecated) Use generation_config.emotion instead. generationConfig: allOf: - $ref: >- #/components/schemas/ultravox.v1.CartesiaVoice_CartesiaGenerationConfig description: Configure the various attributes of the generated speech. description: >- Specification for a voice served by Cartesia. See https://docs.cartesia.ai/api-reference/tts/websocket ultravox.v1.LmntVoice: type: object properties: voiceId: type: string description: The ID of the voice in LMNT. model: type: string description: The LMNT model to use. speed: type: number description: |- The speaking rate. Must be between 0.25 and 2. Defaults to 1. See https://docs.lmnt.com/api-reference/speech/synthesize-speech-bytes#body-speed format: float conversational: type: boolean description: >- See https://docs.lmnt.com/api-reference/speech/synthesize-speech-bytes#body-conversational description: Specification for a voice served by LMNT. ultravox.v1.GoogleVoice: type: object properties: voiceId: type: string description: The ID (name) of the voice in Google, e.g. "en-US-Chirp3-HD-Charon". speakingRate: type: number description: |- The speaking rate. Must be between 0.25 and 2. Defaults to 1. See https://cloud.google.com/python/docs/reference/texttospeech/latest/google.cloud.texttospeech_v1.types.StreamingAudioConfig format: float description: |- Specification for a voice served by Google. This implementation uses bidirectional streaming, so voices prior to Chirp3 are not supported. ultravox.v1.InworldVoice: type: object properties: voiceId: type: string description: The ID of the voice in Inworld. modelId: type: string description: >- The ID of the model to use for generations, e.g. "inworld-tts-1-max". See https://docs.inworld.ai/docs/tts/tts-models speakingRate: type: number description: |- The speaking rate. Must be between 0.5 and 1.5. Defaults to 1. See https://docs.inworld.ai/api-reference/ttsAPI/texttospeech/synthesize-speech-stream#body-audio-config-speaking-rate format: float temperature: type: number description: >- How much randomness to use when sampling audio tokens. Must be between 0.0 and 2.0. See https://docs.inworld.ai/api-reference/ttsAPI/texttospeech/synthesize-speech-stream#body-temperature format: float applyTextNormalization: type: boolean description: >- Whether or not to apply text normalization. This should typically only be disabled if the agent is instructed to normalize text directly. See https://docs.inworld.ai/api-reference/ttsAPI/texttospeech/synthesize-speech-stream#body-apply-text-normalization. description: Specification for a voice served by Inworld. ultravox.v1.RespeecherVoice: type: object properties: voiceId: type: string description: The ID of the voice in Respeecher. model: type: string description: >- The model to use, e.g. "/v1/public/tts/ua-rt" or "/v1/public/tts/en-rt" Requests will be sent to wss://api.respeecher.com{model}/tts/websocket. If not set, defaults to "/v1/public/tts/en-rt" for calls with an English language hint and "/v1/public/tts/ua-rt" otherwise. seed: type: integer description: Random seed for reproducible generation. format: int32 temperature: type: number description: >- Controls randomness of the output. Higher values produce more varied speech. If set, must be greater than or equal to 0.0. format: float topK: type: integer description: |- Limits sampling to the top K most likely tokens. If set, must be exactly -1 or greater than 0. format: int32 topP: type: number description: >- Limits sampling to tokens with cumulative probability up to this value. If set, must be greater than 0 and less than or equal to 1.0. format: float minP: type: number description: |- Minimum probability threshold for token sampling. If set, must be between 0.0 and 1.0, inclusive. format: float presencePenalty: type: number description: |- Penalty for tokens already present in the context. If set, must be between 0 and 2, inclusive. format: float repetitionPenalty: type: number description: |- Penalty for repeating tokens. If set, must be between 1 and 2, inclusive. format: float frequencyPenalty: type: number description: |- Penalty based on token frequency. If set, must be between 0 and 2, inclusive. format: float description: |- Specification for a voice served by Respeecher. See https://space.respeecher.com/docs/api/tts/sampling-params-guide for parameter guidance. ultravox.v1.GenericVoice: type: object properties: url: type: string description: The endpoint to which requests are sent. headers: type: object additionalProperties: type: string description: Headers to include in the request. body: type: object description: >- The request body to send. Some field should include a placeholder for text represented as {text}. The placeholder will be replaced with the text to synthesize. responseSampleRate: type: integer description: The sample rate of the audio returned by the API. format: int32 responseWordsPerMinute: type: integer description: >- An estimate of the speaking rate of the returned audio in words per minute. This is used for transcript timing while audio is streamed in the response. (Once the response is complete, Ultravox Realtime uses the real audio duration to adjust the timing.) Defaults to 150 and is unused for non-streaming responses. format: int32 responseMimeType: type: string description: >- The real mime type of the content returned by the API. If unset, the Content-Type response header will be used. This is useful for APIs whose response bodies don't strictly adhere to what the API claims via header. For example, if your API claims to return audio/wav but omits the WAV header (thus really returning raw PCM), set this to audio/l16. Similarly, if your API claims to return JSON but actually streams JSON Lines, set this to application/jsonl. jsonAudioFieldPath: type: string description: >- For JSON responses, the path to the field containing base64-encoded audio data. The data must be PCM audio, optionally with a WAV header. jsonByteEncoding: enum: - JSON_BYTE_ENCODING_UNSPECIFIED - JSON_BYTE_ENCODING_BASE64 - JSON_BYTE_ENCODING_HEX type: string description: >- For JSON responses, how audio bytes are encoded into the json_audio_field_path string. Defaults to base64. Also supports hex. format: enum description: >- Specification for a voice served by some generic REST-based TTS API. The API must accept an application/json POST request (as defined below) and return either WAV audio, raw PCM audio, or application/json with a base64 encoded audio data field that itself corresponds to WAV or raw PCM audio. Note that this simple API implies a lack of either input streaming or audio timing information, so more specific voice types are preferable when available. ultravox.v1.ElevenLabsVoice_PronunciationDictionaryReference: type: object properties: dictionaryId: type: string description: The dictionary's ID. versionId: type: string description: The dictionary's version. description: A reference to a pronunciation dictionary within ElevenLabs. ultravox.v1.CartesiaVoice_CartesiaGenerationConfig: type: object properties: volume: type: number description: >- Adjust the volume of the generated speech between 0.5x and 2.0x the original volume (default is 1.0x). Valid values are between [0.5, 2.0] inclusive. format: float speed: type: number description: >- Adjust the speed of the generated speech between 0.6x and 2.0x the original speed (default is 1.0x). Valid values are between [0.6, 1.5] inclusive. format: float emotion: type: string description: >- The primary emotions are neutral, calm, angry, content, sad, scared. For more options, see Prompting Sonic-3. pronunciationDictId: type: string description: |- The ID of a pronunciation dictionary to use for the generation. Pronunciation dictionaries are supported by sonic-3 models and newer. See https://docs.cartesia.ai/build-with-cartesia/capability-guides/specify-custom-pronunciations description: Cartesia generation configuration for Sonic-3 and later models. securitySchemes: apiKeyAuth: type: apiKey in: header name: X-API-Key description: API key ````