hermes-agent/website/docs/user-guide/features/tts.md

sidebar_position, title, description

sidebar_position	title	description
9	Voice & TTS	Text-to-speech and voice message transcription across all platforms

Voice & TTS

Hermes Agent supports both text-to-speech output and voice message transcription across all messaging platforms.

:::tip Nous Subscribers If you have a paid Nous Portal subscription, OpenAI TTS is available through the Tool Gateway without a separate OpenAI API key. Run hermes model or hermes tools to enable it. :::

Text-to-Speech

Convert text to speech with ten providers:

Provider	Quality	Cost	API Key
Edge TTS (default)	Good	Free	None needed
ElevenLabs	Excellent	Paid	ELEVENLABS_API_KEY
OpenAI TTS	Good	Paid	VOICE_TOOLS_OPENAI_KEY
MiniMax TTS	Excellent	Paid	MINIMAX_API_KEY
Mistral (Voxtral TTS)	Excellent	Paid	MISTRAL_API_KEY
Google Gemini TTS	Excellent	Free tier	GEMINI_API_KEY
xAI TTS	Excellent	Paid	XAI_API_KEY
NeuTTS	Good	Free (local)	None needed
KittenTTS	Good	Free (local)	None needed
Piper	Good	Free (local)	None needed

Platform Delivery

Platform	Delivery	Format
Telegram	Voice bubble (plays inline)	Opus .ogg
Discord	Voice bubble (Opus/OGG), falls back to file attachment	Opus/MP3
WhatsApp	Audio file attachment	MP3
CLI	Saved to ~/.hermes/audio_cache/	MP3

Configuration

# In ~/.hermes/config.yaml
tts:
  provider: "edge"              # "edge" | "elevenlabs" | "openai" | "minimax" | "mistral" | "gemini" | "xai" | "neutts" | "kittentts" | "piper"
  speed: 1.0                    # Global speed multiplier (provider-specific settings override this)
  edge:
    voice: "en-US-AriaNeural"   # 322 voices, 74 languages
    speed: 1.0                  # Converted to rate percentage (+/-%)
  elevenlabs:
    voice_id: "pNInz6obpgDQGcFmaJgB"  # Adam
    model_id: "eleven_multilingual_v2"
  openai:
    model: "gpt-4o-mini-tts"
    voice: "alloy"              # alloy, echo, fable, onyx, nova, shimmer
    base_url: "https://api.openai.com/v1"  # Override for OpenAI-compatible TTS endpoints
    speed: 1.0                  # 0.25 - 4.0
  minimax:
    model: "speech-2.8-hd"     # speech-2.8-hd (default), speech-2.8-turbo
    voice_id: "English_Graceful_Lady"  # See https://platform.minimax.io/faq/system-voice-id
    speed: 1                    # 0.5 - 2.0
    vol: 1                      # 0 - 10
    pitch: 0                    # -12 - 12
  mistral:
    model: "voxtral-mini-tts-2603"
    voice_id: "c69964a6-ab8b-4f8a-9465-ec0925096ec8"  # Paul - Neutral (default)
  gemini:
    model: "gemini-2.5-flash-preview-tts"  # or gemini-2.5-pro-preview-tts
    voice: "Kore"               # 30 prebuilt voices: Zephyr, Puck, Kore, Enceladus, Gacrux, etc.
  xai:
    voice_id: "eve"             # xAI TTS voice (see https://docs.x.ai/docs/api-reference#tts)
    language: "en"              # ISO 639-1 code
    sample_rate: 24000          # 22050 / 24000 (default) / 44100 / 48000
    bit_rate: 128000            # MP3 bitrate; only applies when codec=mp3
    # base_url: "https://api.x.ai/v1"   # Override via XAI_BASE_URL env var
  neutts:
    ref_audio: ''
    ref_text: ''
    model: neuphonic/neutts-air-q4-gguf
    device: cpu
  kittentts:
    model: KittenML/kitten-tts-nano-0.8-int8   # 25MB int8; also: kitten-tts-micro-0.8 (41MB), kitten-tts-mini-0.8 (80MB)
    voice: Jasper                               # Jasper, Bella, Luna, Bruno, Rosie, Hugo, Kiki, Leo
    speed: 1.0                                  # 0.5 - 2.0
    clean_text: true                            # Expand numbers, currencies, units
  piper:
    voice: en_US-lessac-medium                  # voice name (auto-downloaded) OR absolute path to .onnx
    # voices_dir: ''                            # default: ~/.hermes/cache/piper-voices/
    # use_cuda: false                           # requires onnxruntime-gpu
    # length_scale: 1.0                         # 2.0 = twice as slow
    # noise_scale: 0.667
    # noise_w_scale: 0.8
    # volume: 1.0                               # 0.5 = half as loud
    # normalize_audio: true

Speed control: The global tts.speed value applies to all providers by default. Each provider can override it with its own speed setting (e.g., tts.openai.speed: 1.5). Provider-specific speed takes precedence over the global value. Default is 1.0 (normal speed).

Telegram Voice Bubbles & ffmpeg

Telegram voice bubbles require Opus/OGG audio format:

• OpenAI, ElevenLabs, and Mistral produce Opus natively — no extra setup
• Edge TTS (default) outputs MP3 and needs ffmpeg to convert:
• MiniMax TTS outputs MP3 and needs ffmpeg to convert for Telegram voice bubbles
• Google Gemini TTS outputs raw PCM and uses ffmpeg to encode Opus directly for Telegram voice bubbles
• xAI TTS outputs MP3 and needs ffmpeg to convert for Telegram voice bubbles
• NeuTTS outputs WAV and also needs ffmpeg to convert for Telegram voice bubbles
• KittenTTS outputs WAV and also needs ffmpeg to convert for Telegram voice bubbles
• Piper outputs WAV and also needs ffmpeg to convert for Telegram voice bubbles

# Ubuntu/Debian
sudo apt install ffmpeg

# macOS
brew install ffmpeg

# Fedora
sudo dnf install ffmpeg

Without ffmpeg, Edge TTS, MiniMax TTS, NeuTTS, KittenTTS, and Piper audio are sent as regular audio files (playable, but shown as a rectangular player instead of a voice bubble).

:::tip If you want voice bubbles without installing ffmpeg, switch to the OpenAI, ElevenLabs, or Mistral provider. :::

Piper (local, 44 languages)

Piper is a fast, local neural TTS engine from the Open Home Foundation (the Home Assistant maintainers). It runs entirely on CPU, supports 44 languages with pre-trained voices, and needs no API key.

Install via hermes tools → Voice & TTS → Piper — Hermes runs pip install piper-tts for you. Or install manually: pip install piper-tts.

Switch to Piper:

tts:
  provider: piper
  piper:
    voice: en_US-lessac-medium

On the first TTS call for a voice that isn't cached locally, Hermes runs python -m piper.download_voices <name> and downloads the model (~20-90MB depending on quality tier) into ~/.hermes/cache/piper-voices/. Subsequent calls reuse the cached model.

Picking a voice. The full voice catalog covers English, Spanish, French, German, Italian, Dutch, Portuguese, Russian, Polish, Turkish, Chinese, Arabic, Hindi, and more — each with x_low / low / medium / high quality tiers. Sample voices at rhasspy.github.io/piper-samples.

Using a pre-downloaded voice. Set tts.piper.voice to an absolute path ending in .onnx:

tts:
  piper:
    voice: /path/to/my-custom-voice.onnx

Advanced knobs (tts.piper.length_scale / noise_scale / noise_w_scale / volume / normalize_audio, use_cuda) correspond 1:1 to Piper's SynthesisConfig. They're ignored on older piper-tts versions.

Custom command providers

If a TTS engine you want isn't natively supported (VoxCPM, MLX-Kokoro, XTTS CLI, a voice-cloning script, anything else that exposes a CLI), you can wire it in as a command-type provider without writing any Python. Hermes writes the input text to a temp UTF-8 file, runs your shell command, and reads the audio file the command produced.

Declare one or more providers under tts.providers.<name> and switch between them with tts.provider: <name> — the same way you switch between built-ins like edge and openai.

tts:
  provider: voxcpm                 # pick any name under tts.providers
  providers:
    voxcpm:
      type: command
      command: "voxcpm --ref ~/voice.wav --text-file {input_path} --out {output_path}"
      output_format: mp3
      timeout: 180
      voice_compatible: true       # try to deliver as a Telegram voice bubble

    mlx-kokoro:
      type: command
      command: "python -m mlx_kokoro --in {input_path} --out {output_path} --voice {voice}"
      voice: af_sky
      output_format: wav

    piper-custom:                  # native Piper also supports custom .onnx via tts.piper.voice
      type: command
      command: "piper -m /path/to/custom.onnx -f {output_path} < {input_path}"
      output_format: wav

Placeholders

Your command template can reference these placeholders. Hermes substitutes them at render time and shell-quotes each value for the surrounding context (bare / single-quoted / double-quoted), so paths with spaces and other shell-sensitive characters are safe.

Placeholder	Meaning
{input_path}	Path to the temp UTF-8 text file Hermes wrote
{text_path}	Alias for {input_path}
{output_path}	Path the command must write audio to
{format}	mp3 / wav / ogg / flac
{voice}	tts.providers.<name>.voice, empty when unset
{model}	tts.providers.<name>.model
{speed}	Resolved speed multiplier (provider or global)

Use {{ and }} for literal braces.

Optional keys

Key	Default	Meaning
timeout	120	Seconds; the process tree is killed on expiry (Unix killpg, Windows taskkill /T).
output_format	mp3	One of mp3 / wav / ogg / flac. Auto-inferred from the output extension if Hermes picks a path.
voice_compatible	false	When true, Hermes converts MP3/WAV output to Opus/OGG via ffmpeg so Telegram renders a voice bubble.
max_text_length	5000	Input is truncated to this length before rendering the command.
voice / model	empty	Passed to the command as placeholder values only.

Behavior notes

• Built-in names always win. A tts.providers.openai entry never shadows the native OpenAI provider, so no user config can silently replace a built-in.
• Default delivery is a document. Command providers deliver as regular audio attachments on every platform. Opt in to voice-bubble delivery per-provider with voice_compatible: true.
• Command failures surface to the agent. Non-zero exit, empty output, or timeout all return an error with the command's stderr/stdout included so you can debug the provider from the conversation.
• type: command is the default when command: is set. Writing type: command explicitly is good practice but not required; an entry with a non-empty command string is treated as a command provider.
• {input_path} / {text_path} are interchangeable. Use whichever reads better in your command.

Security

Command-type providers run whatever shell command you configure, with your user's permissions. Hermes quotes placeholder values and enforces the configured timeout, but the command template itself is trusted local input — treat it the same way you would a shell script on your PATH.

Voice Message Transcription (STT)

Voice messages sent on Telegram, Discord, WhatsApp, Slack, or Signal are automatically transcribed and injected as text into the conversation. The agent sees the transcript as normal text.

Provider	Quality	Cost	API Key
Local Whisper (default)	Good	Free	None needed
Groq Whisper API	Good–Best	Free tier	GROQ_API_KEY
OpenAI Whisper API	Good–Best	Paid	VOICE_TOOLS_OPENAI_KEY or OPENAI_API_KEY

:::info Zero Config Local transcription works out of the box when faster-whisper is installed. If that's unavailable, Hermes can also use a local whisper CLI from common install locations (like /opt/homebrew/bin) or a custom command via HERMES_LOCAL_STT_COMMAND. :::

Configuration

# In ~/.hermes/config.yaml
stt:
  provider: "local"           # "local" | "groq" | "openai" | "mistral" | "xai"
  local:
    model: "base"             # tiny, base, small, medium, large-v3
  openai:
    model: "whisper-1"        # whisper-1, gpt-4o-mini-transcribe, gpt-4o-transcribe
  mistral:
    model: "voxtral-mini-latest"  # voxtral-mini-latest, voxtral-mini-2602
  xai:
    model: "grok-stt"         # xAI Grok STT

Provider Details

Local (faster-whisper) — Runs Whisper locally via faster-whisper. Uses CPU by default, GPU if available. Model sizes:

Model	Size	Speed	Quality
tiny	~75 MB	Fastest	Basic
base	~150 MB	Fast	Good (default)
small	~500 MB	Medium	Better
medium	~1.5 GB	Slower	Great
large-v3	~3 GB	Slowest	Best

Groq API — Requires GROQ_API_KEY. Good cloud fallback when you want a free hosted STT option.

OpenAI API — Accepts VOICE_TOOLS_OPENAI_KEY first and falls back to OPENAI_API_KEY. Supports whisper-1, gpt-4o-mini-transcribe, and gpt-4o-transcribe.

Mistral API (Voxtral Transcribe) — Requires MISTRAL_API_KEY. Uses Mistral's Voxtral Transcribe models. Supports 13 languages, speaker diarization, and word-level timestamps. Install with pip install hermes-agent[mistral].

xAI Grok STT — Requires XAI_API_KEY. Posts to https://api.x.ai/v1/stt as multipart/form-data. Good choice if you're already using xAI for chat or TTS and want one API key for everything. Auto-detection order puts it after Groq — explicitly set stt.provider: xai to force it.

Custom local CLI fallback — Set HERMES_LOCAL_STT_COMMAND if you want Hermes to call a local transcription command directly. The command template supports {input_path}, {output_dir}, {language}, and {model} placeholders.

Fallback Behavior

If your configured provider isn't available, Hermes automatically falls back:

• Local faster-whisper unavailable → Tries a local whisper CLI or HERMES_LOCAL_STT_COMMAND before cloud providers
• Groq key not set → Falls back to local transcription, then OpenAI
• OpenAI key not set → Falls back to local transcription, then Groq
• Mistral key/SDK not set → Skipped in auto-detect; falls through to next available provider
• Nothing available → Voice messages pass through with an accurate note to the user