Text to Speech

Overview

The Text to Speech API converts text into audio with any of 9 TTS models. The default, bulbul:v3, has 37 voices across 11 Indian languages.

Four models are on the free tier: bulbul:v3, aura-2-en, aura-2-es and melotts.

Endpoint: POST /v1/audio/speech

1. 1

   Your app

   Send text + a and to

2. 2

   Your chosen model

   Synthesize speech in the chosen voice — if is omitted

3. 3

   Your app

   Receive the audio stream and play or save it

Basic Usage

from openai import OpenAI

client = OpenAI(
    api_key="cm_your_key",
    base_url="https://api.callmissed.com/v1"
)

response = client.audio.speech.create(
    model="bulbul:v3",
    voice="shubh",
    input="Namaste, kaise hain aap?"
)

response.stream_to_file("speech.mp3")

Parameters

Send a JSON body.

Audio Formats

response_format accepts mp3, opus, aac, flac, wav or pcm, but not every model can produce every format. The Content-Type response header always describes the audio actually returned, so read it rather than assuming the format you asked for.

Errors

Errors use the OpenAI envelope: {"error": {"message", "type", "code"}}.

Making speech sound human

Naturalness comes from three places, in order of impact:

1. The text you send. Every engine sounds more human when the input reads like speech rather than like a screen. humanize (on by default) handles the mechanical part — markdown, emoji, https://callmissed.com → "callmissed dot com", 2039123456 → 203.912.3456. Beyond that, write short sentences and use contractions; if an LLM generates your text, tell it that its output will be spoken aloud.

2. Expressiveness parameters, where the model supports them:

# bulbul:v3 — temperature is its expressiveness control
curl -X POST https://api.callmissed.com/v1/audio/speech \
  -H "Authorization: Bearer cm_your_key" \
  -H "Content-Type: application/json" \
  -d '{"model": "bulbul:v3", "input": "Bilkul, main abhi check karta hoon.", "voice": "shubh", "temperature": 1.1}' \
  --output speech.mp3

# gpt-4o-mini-tts — direct the performance in plain language
curl -X POST https://api.callmissed.com/v1/audio/speech \
  -H "Authorization: Bearer cm_your_key" \
  -H "Content-Type: application/json" \
  -d '{"model": "gpt-4o-mini-tts", "input": "Your order shipped this morning.", "voice": "nova", "instructions": "Cheerful and upbeat, like sharing good news with a friend."}' \
  --output speech.mp3

3. Pauses in the text. deepgram-aura-2, deepgram-aura-1, aura-2-en and aura-2-es read pause cues written into your text: ... gives a longer natural pause, a comma or period gives a short one, and um/uh render as natural hesitation.

{"model": "deepgram-aura-2", "input": "Let me pull that up... okay, found it."}

bulbul:v3 and gnani-timbre-v2.0 do not support pause markup or SSML — they would speak the dots aloud. Use sentence length and real punctuation for rhythm on those models.

Choosing an expressive voice

Streaming (Deepgram Aura)

For deepgram-aura-2 and deepgram-aura-1, set "stream": true to receive audio frames as they're synthesized, as a chunked HTTP response. Ideal for real-time playback where you want the first audio bytes as fast as possible.

Streaming supports raw encodings only — response_format must be linear16 (or pcm/wav), mulaw, or alaw. Compressed formats (mp3, opus, aac, flac) cannot be streamed; if you request one with stream:true, the full audio is returned in one buffered response instead.

curl -N -X POST https://api.callmissed.com/v1/audio/speech \
  -H "Authorization: Bearer cm_your_key" \
  -H "Content-Type: application/json" \
  -d '{"model": "deepgram-aura-2", "voice": "thalia", "input": "Streaming hello.", "response_format": "linear16", "stream": true}' \
  --output speech.raw

Billing is identical to the non-streaming path (per character). Other providers ignore stream and return the full audio in one response.