Bland BTTS Text to Speech and Voice Cloning API

Bland BTTS

curl --request POST \
  --url https://api.novita.ai/v3/bland-tts/v2/tts

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.novita.ai/v3/bland-tts/v2/tts",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.novita.ai/v3/bland-tts/v2/tts"

	req, _ := http.NewRequest("POST", url, nil)

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

require 'uri'
require 'net/http'

url = URI("https://api.novita.ai/v3/bland-tts/v2/tts")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)

response = http.request(request)
puts response.read_body

POST

bland-tts

tts

Bland BTTS

curl --request POST \
  --url https://api.novita.ai/v3/bland-tts/v2/tts

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.novita.ai/v3/bland-tts/v2/tts",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.novita.ai/v3/bland-tts/v2/tts"

	req, _ := http.NewRequest("POST", url, nil)

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

require 'uri'
require 'net/http'

url = URI("https://api.novita.ai/v3/bland-tts/v2/tts")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)

response = http.request(request)
puts response.read_body

1. Overview

This document describes how to use speech synthesis and voice cloning through the Bland BTTS native protocol. Both endpoints are synchronous: a POST request returns the result directly, with no need to create a task and poll for the result.

1.1 Endpoints

Capability	Method and path
Speech synthesis	`POST /v3/bland-tts/v2/tts`
Voice cloning	`POST /v3/bland-tts/v1/voices/clone`

The full address in the examples in this document is https://api.novita.ai plus the endpoint path in the table above, where https://api.novita.ai is the API domain you use.

1.2 Authentication

All requests must carry the platform API Key:

Authorization: Bearer <YOUR_API_KEY>

Speech synthesis requests must also specify the JSON content type (Content-Type: application/json); voice cloning requests use multipart/form-data and do not need to specify the content type separately (the HTTP client generates it automatically, including the boundary).

1.3 Response Structure

On success, speech synthesis returns audio binary data directly, not JSON. See “2. Speech Synthesis” for details.
On success, voice cloning returns JSON, where data.voice_id is the UUID of the newly cloned voice and can be used directly as the voice field of the speech synthesis endpoint.
When the two endpoints fail, they return different JSON error structures. See the “Common Errors” section of each endpoint.

2. Speech Synthesis

Official parameter reference: Speak

2.1 Endpoint

POST https://api.novita.ai/v3/bland-tts/v2/tts

Common request fields:

Field	Type	Required	Description
`text`	string	Yes	Text to synthesize, up to 5000 characters. Supports pause syntax, such as `<`.
`voice`	string	Yes	Voice UUID (voice names are not accepted). Use the official List Voices endpoint to look it up, or use the `voice_id` produced by the voice cloning endpoint.
`audio`	object	No	Output audio format configuration. All sub-fields are optional.
`audio.encoding`	string	No	Defaults to `pcm_s16le`. Options are `pcm_s16le` (16-bit signed little-endian PCM) or `mulaw` (8-bit mu-law, fixed at 8kHz, for telephony scenarios).
`audio.sample_rate`	number	No	Defaults to 48000. Options are 8000/16000/24000/44100/48000; fixed at 8000 when `encoding=mulaw`.
`audio.container`	string	No	Defaults to `raw`. Options are `raw` (raw frames, suitable for streaming scenarios) or `wav` (a complete RIFF/WAVE file, suitable for download and storage).
`controls`	object	No	Voice expressiveness controls. All sub-fields are optional, with a range of 0.0–1.0, and take effect only on BTTS_V3 voices.
`controls.expressiveness`	number	No	Higher values make the intonation richer and more varied; lower values make it flatter and more uniform.
`controls.stability`	number	No	Higher values make repeated synthesis results more consistent; lower values increase expressiveness but also variability.

2.2 Example

curl -X POST 'https://api.novita.ai/v3/bland-tts/v2/tts' \
  -H 'Authorization: Bearer <YOUR_API_KEY>' \
  -H 'Content-Type: application/json' \
  -d '{
    "text": "Hello world",
    "voice": "<voice_id>",
    "audio": {
      "container": "wav"
    }
  }'

2.3 Response

On success, the endpoint returns audio binary data directly (HTTP 200), not JSON. The Content-Type varies with the request’s audio.container/audio.encoding (for example, audio/wav, audio/pcm). In practice, the transparent proxy returns the upstream X-Sample-Rate response header unchanged (the sample rate of the synthesized audio); other response headers documented by Bland, such as x-request-id/x-model/x-voice-id/x-cost/x-latency, were not observed in testing. Do not rely on these headers.

2.4 Billing

Request cost = unit price (per thousand characters) × number of characters in text / 1000

The character count is calculated from the text field. Chinese characters (Han characters) count as 2 characters, and other characters (including English letters, digits, spaces, and punctuation) count as 1 character. The exact unit price depends on the pricing page of the service you use.

3. Voice Cloning

Official parameter reference: Clone Voice

3.1 Endpoint

POST https://api.novita.ai/v3/bland-tts/v1/voices/clone

The request body is multipart/form-data. Common fields:

Field	Type	Required	Description
`name`	string	Yes	Display name of the cloned voice, 1–30 characters. Must be unique within your voice library.
`audio_samples`	file	Yes	Audio sample file. Regardless of which engine is used (V2 or V3), only a single file is accepted. About 10 seconds is recommended, with a maximum of 10MB.
`gender`	string	No	`male` or `female`. Optional but recommended, as it helps the underlying model.
`description`	string	No	Free-form text description, provided to the model as supplementary context for tone and style.
`isBTTS_V3`	string	No	When the value is the string `"true"`, the V3 engine is used (the default when neither engine flag is set).
`isBTTS_V2`	string	No	When the value is the string `"true"`, the V2 engine is used (choose one of `isBTTS_V3` and `isBTTS_V2`).

isBTTS_V3/isBTTS_V2 are boolean-semantic fields, but because the request body is multipart/form-data rather than JSON, they must be sent as the string "true".

3.2 Example

curl -X POST 'https://api.novita.ai/v3/bland-tts/v1/voices/clone' \
  -H 'Authorization: Bearer <YOUR_API_KEY>' \
  -F 'name=my-cloned-voice' \
  -F 'audio_samples=@sample.wav;type=audio/wav'

3.3 Response

On success, the endpoint returns (HTTP 200):

{
  "status": 200,
  "data": {
    "voice_id": "<voice_id>",
    "name": "my-cloned-voice"
  },
  "errors": null
}

Field	Type	Description
`status`	integer	HTTP status code, 200 on success.
`data.voice_id`	string	UUID of the newly cloned voice, used directly as the `voice` field of the speech synthesis endpoint.
`data.name`	string	Echoes the display name provided in the request.
`errors`	null/array	`null` on success.

Verified in practice: passing the voice_id produced by the cloning endpoint directly to the voice field of the speech synthesis endpoint returns real synthesized audio with HTTP 200, so the two endpoints can be used in sequence directly.

3.4 Billing

The voice cloning endpoint is always free of charge and generates no cost.

3.5 Common Errors

{
  "status": 400,
  "data": null,
  "errors": [
    { "error": "<error type>", "message": "<error message>" }
  ]
}

Scenario	Response recorded in the official documentation	Description
Request is missing a required field	HTTP 400, error: “Validation Error”	For example, when the `audio_samples` file is not provided.
The account has reached the plan’s voice limit	The official documentation records HTTP 400, error: “Limit Exceeded”, message: “You have reached the maximum number of voices for your plan.”	The actual response observed in testing is HTTP 500, `{"data":null,"errors":[{"error":"INTERNAL_SERVER_ERROR","message":"You have reached the maximum number of voices for your plan."}]}`. Use the observed behavior (HTTP 500) as the source of truth and do not assume this scenario returns 400.

When the account has reached its voice limit, you need to top up the Bland account wallet to increase the quota. This is unrelated to the faas-backend configuration.

4. Common Errors and Notes

Error structure of the speech synthesis endpoint:

{ "error": { "code": "<error code>", "message": "<error message>" } }

HTTP	code	Common scenario	Suggested handling
400	`invalid_request`	A required field is missing or incorrectly formatted.	Fix the request based on the error message.
400	`text_too_long`	`text` exceeds 5000 characters.	Shorten the text or split it into multiple requests.
400	`unsupported_encoding`	`audio.encoding` is not an allowed value.	Check whether the value is `pcm_s16le`/`mulaw`.
400	`unsupported_sample_rate`	`audio.sample_rate` is invalid for the current `encoding`.	Check the sample rate value; `mulaw` is fixed at 8000.
400	`unsupported_container`	`audio.container` is not `raw` or `wav`.	Check the value.
400	`unsupported_voice`	The voice exists but is not BTTS_V2/BTTS_V3.	Switch to a supported voice.
402	`insufficient_credits`	The account balance is insufficient.	Top up the account.
403	`voice_not_live`	The voice is in draft status and has not been published.	Publish the voice and retry.
404	`voice_not_found`	The voice UUID does not exist or is not accessible.	Check the value of the `voice` field.
500	`synthesis_failed`	Synthesis failed before or during streaming.	Retry later; if the failure persists, contact technical support.

The error structure of the voice cloning endpoint is described in “3.5 Common Errors” and is not the same structure as the speech synthesis endpoint. Do not mix them up. Other notes:

The speech synthesis endpoint request body requires the JSON content type; the voice cloning endpoint request body is multipart/form-data and must not be called with JSON.
A voice_id created by voice cloning is shared among all callers under the current API Key, and the system does not record “which caller cloned which voice”. Manage voice ownership and visibility in your own business layer, and do not assume the platform isolates voices between callers.
The optional fields of the voice cloning endpoint (gender/description/isBTTS_V3/isBTTS_V2) have not been fully validated with real requests. It is recommended to test them yourself before launch to confirm that the behavior meets expectations.
When the response is audio binary data, process it directly according to the returned Content-Type and do not attempt to parse it as JSON.

Last modified on October 21, 2026

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Overview

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Bland BTTS

1. Overview

1.1 Endpoints

1.2 Authentication

1.3 Response Structure

2. Speech Synthesis

2.1 Endpoint

2.2 Example

2.3 Response

2.4 Billing

3. Voice Cloning

3.1 Endpoint

3.2 Example

3.3 Response

3.4 Billing

3.5 Common Errors

4. Common Errors and Notes

​1. Overview

​1.1 Endpoints

​1.2 Authentication

​1.3 Response Structure

​2. Speech Synthesis

​2.1 Endpoint

​2.2 Example

​2.3 Response

​2.4 Billing

​3. Voice Cloning

​3.1 Endpoint

​3.2 Example

​3.3 Response

​3.4 Billing

​3.5 Common Errors

​4. Common Errors and Notes

1. Overview

1.1 Endpoints

1.2 Authentication

1.3 Response Structure

2. Speech Synthesis

2.1 Endpoint

2.2 Example

2.3 Response

2.4 Billing

3. Voice Cloning

3.1 Endpoint

3.2 Example

3.3 Response

3.4 Billing

3.5 Common Errors

4. Common Errors and Notes