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AWS Polly UnsupportedPlsAlphabetException

The PLS alphabet specified is not supported.

Understanding AWS Polly

AWS Polly is a service provided by Amazon Web Services that turns text into lifelike speech, allowing developers to create applications that can 'speak'. It is widely used in applications that require voice interaction, such as virtual assistants, e-learning platforms, and more. Polly supports multiple languages and offers a variety of voices to choose from, making it a versatile tool for voice synthesis.

Recognizing the Symptom

When working with AWS Polly, you might encounter the UnsupportedPlsAlphabetException. This error typically manifests when you attempt to use a phoneme alphabet that Polly does not support. The error message might look something like this:

{
"__type": "UnsupportedPlsAlphabetException",
"message": "The PLS alphabet specified is not supported."
}

Exploring the Issue

The UnsupportedPlsAlphabetException occurs when the Speech Synthesis Markup Language (SSML) input contains a phoneme element with an alphabet attribute that Polly does not recognize. Polly supports specific phoneme alphabets, and using an unsupported one will trigger this exception.

Common Causes

  • Using a custom or incorrect phoneme alphabet in SSML.
  • Typographical errors in the alphabet attribute.

Steps to Fix the Issue

To resolve the UnsupportedPlsAlphabetException, follow these steps:

1. Verify Supported Alphabets

Ensure that you are using a supported phoneme alphabet. AWS Polly supports the following phoneme alphabets:

  • ipa - International Phonetic Alphabet
  • x-sampa - Extended Speech Assessment Methods Phonetic Alphabet

Refer to the AWS Polly Documentation for more details on supported alphabets.

2. Update Your SSML

If your SSML contains an unsupported alphabet, update it to use one of the supported alphabets. For example, change:

<phoneme alphabet="unsupported-alphabet" ph="tɛst">test</phoneme>

To:

<phoneme alphabet="ipa" ph="tɛst">test</phoneme>

3. Test Your Changes

After making the necessary changes, test your SSML input with AWS Polly to ensure that the error is resolved. You can use the AWS Polly Console to synthesize speech and verify the output.

Conclusion

By ensuring that you use a supported phoneme alphabet in your SSML input, you can avoid the UnsupportedPlsAlphabetException and ensure smooth operation of your AWS Polly-based applications. For further assistance, consult the AWS Polly Developer Guide.

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