AWS Polly

AWS Polly is a cloud-based text-to-speech service that produces natural-sounding neural speech. It accepts IPA directly through SSML, so there is no phoneme conversion step – what you write in your phonetic inventory is what Polly tries to pronounce.

NOTE

If you just want the configuration fields, skip to Configuration.

Setup

Enable the feature flag when building:

cargo build --features voice-polly

Polly requires AWS credentials. The simplest method is to set environment variables:

export AWS_ACCESS_KEY_ID=your-key
export AWS_SECRET_ACCESS_KEY=your-secret
export AWS_REGION=us-east-1

Alternatively, configure ~/.aws/credentials using the AWS CLI. The region determines which voices are available – most voices exist in us-east-1.

You can verify that credentials are working by running conlang config voice scan, which queries the Polly API and lists available voices for your configured region.

Configuration

Each Polly voice entry requires "driver": "polly" and accepts the following optional fields:

A minimal entry:

{
  "driver": "polly"
}

This uses the Joanna voice with the neural engine.

A multi-voice setup:

{
  "polly-joanna": {
    "driver": "polly",
    "voice_id": "Joanna",
    "engine": "neural"
  },
  "polly-matthew": {
    "driver": "polly",
    "voice_id": "Matthew",
    "engine": "standard"
  }
}

The "neural" engine produces higher-quality speech but is not available for every voice ID. The "standard" engine is available for all voices and is less expensive per character.

How IPA Reaches Polly

When you speak through a Polly voice, the toolkit wraps your IPA string in an SSML <phoneme> tag:

<phoneme alphabet="ipa" ph="ˈpa.ta">.</phoneme>

Polly interprets the IPA directly, so there is no lossy conversion step. This gives Polly higher IPA fidelity than eSpeak-ng for most sounds, though Polly’s phoneme support is limited to the sounds that exist in its voice’s base language.

Discovering Voices

Run conlang config voice scan to query the Polly DescribeVoices API:

conlang config voice scan

This lists every voice available in your configured AWS region, along with the voice ID, language, and supported engines. Use the voice IDs from this list as the "voice_id" value in your configuration.