Amazon Polly

Amazon Polly represents a significant advancement in artificial intelligence-driven text-to-speech technology. When you text "What's the weather like today?" to your smart home device, you're likely hearing the neural voice generated by Amazon Polly. This powerful service can create lifelike speech across 47 languages, making it a versatile tool for developers building applications ranging from virtual assistants to language learning tools. In this article, we'll explore how Amazon Polly processes and stores content securely, the technical capabilities that enable its impressive voice synthesis, and how developers can integrate this technology into their projects while managing costs effectively.

Security and Compliance

Amazon Polly processes and stores content with stringent security measures. The system employs encryption both at rest and in transit, ensuring that only authorized employees can access the data. Technical and physical controls are in place to prevent unauthorized access or disclosure, with a particular focus on user privacy.

The service supports multiple audio formats including MP3, Vorbis, and raw PCM, with sampling rates up to 22 kHz for high-quality audio. Text submissions are stored in encrypted form for up to six months, after which they are deleted unless the user has opted out of content usage for continuous improvement and development purposes. For HIPAA compliance, the service follows the terms of the AWS Business Associate Addendum (AWS BAA) when handling Protected Health Information (PHI).

Content ownership remains with the user, and Amazon Polly uses content only with explicit consent. The service is COPPA-compliant, allowing use in websites, programs, or applications directed at children under age 13, provided users comply with the Amazon Polly Service Terms and obtain the necessary COPPA notices and verifiable parental consent. All content is processed in the AWS region where it is generated, with temporary storage only occurring for service improvement purposes, which users can opt out of through AWS Support.

Technical Specifications

Amazon Polly supports multiple audio formats including MP3, Vorbis, and raw PCM, with sampling rates up to 22 kHz for high-quality audio. The service processes text submissions securely, storing content in encrypted form for up to six months before deletion unless the user has opted out for continuous service improvement purposes.

The technical capabilities of Amazon Polly enable synthesis of lifelike speech across 47 languages, including support for Portuguese (Brazilian), Portuguese (European), Romanian, Russian, Spanish (Spain), Spanish (Mexican), Spanish (US), Swedish, Turkish, and Welsh through various voice engines. These engines include generative, long-form, neural, and standard text-to-speech options, with some voices capable of Newscaster-style narration.

The service provides developers with extensive customization options through Speech Synthesis Markup Language (SSML), allowing control over pronunciation, volume, pitch, and speech rate. Users can also employ custom lexicons to modify pronunciation of specific terms, acronyms, foreign words, and neologisms. Technical documentation details that the service generates audio streams sampled at 8,000 Hz, 16,000 Hz, and 22,050 Hz.

Amazon Polly processes text requests across multiple AWS regions including US East (N. Virginia), US West (Oregon), US East (Ohio), and international locations such as Ireland, Malaysia, Tokyo, Seoul, Singapore, Sydney, Cape Town, London, Frankfurt, and Ireland, with specialized neural voice support in select regions. The service is HIPAA-compliant and eligible for AWS Business Associate Addendum (AWS BAA) when handling Protected Health Information (PHI).

Pricing follows a character-based model with a 12-month free tier offering 500,000 characters per month for standard voices and 100,000 characters for neural TTS voices. Usage beyond the free tier costs $4.00 per million characters for standard voices and $19.20 per million characters for neural TTS voices, with regional pricing differences applicable. Users can cache and replay generated speech at no additional cost while maintaining audio quality through multiple sample rate options.

Voice Options and Customization

Amazon Polly's text-to-speech capabilities can be tailored through multiple voice options and customization features. The service offers three primary voice engines: standard text-to-speech voices, long-form voices, and neural voices. These engines support multiple languages including Portuguese (Brazilian), Portuguese (European), Romanian, Russian, Spanish (Spain), Spanish (Mexican), Spanish (US), Swedish, Turkish, and Welsh.

Voice customization in Amazon Polly is achieved through Speech Synthesis Markup Language (SSML), which allows developers to control various aspects of speech. This includes pronunciation, volume, pitch, and speech rate. Users can modify the way specific words, acronyms, and foreign terms are pronounced by creating custom lexicons. The service also provides advanced capabilities such as detecting specific words or sentences within the text being spoken and generating speech marks using elements of sentence, word, viseme, and SSML.

When used with neural voices, Amazon Polly supports a Newscaster speaking style, making it suitable for professional narration applications. The voice options enable developers to select the ideal engine for their geographic distribution, with the service providing dozens of lifelike voices across 24 languages. This feature set enables creation of natural-sounding audio for applications ranging from e-learning platforms to accessibility tools for visually impaired users.

Pricing and Usage

Pricing for Amazon Polly operates on a character-based model, with usage divided between standard and neural text-to-speech engines. The service offers a generous 12-month free tier including 5 million characters per month for standard voices and 1 million characters per month for neural voices. Beyond the free tier, standard voices cost $4.00 per million characters, while neural voices incur charges at a rate of $19.20 per million characters.

The service also differentiates between US East (N. Virginia), US West (Oregon), and international locations like Europe (Ireland), with regional pricing variations affecting costs. For example, standard voice usage in AWS GovCloud (US) incurs a higher rate of $4.80 per million characters compared to the standard rate of $4.00.

Amazon Polly's usage example calculations demonstrate that each million characters generates approximately 23 hours and 8 minutes of spoken audio. The service allows for significant cost optimization through caching and replaying generated speech without additional charges, making it suitable for applications requiring repeated audio playback.

Integration and Development

Developers can integrate Amazon Polly through the AWS Console, AWS Command Line Interface (AWS CLI), or programmatically using the SynthesizeSpeech API function. The service supports multiple languages and dozens of lifelike voices, allowing developers to select the ideal voice for their geographic distribution.

Audio Output Formats

Amazon Polly supports high-quality audio formats including MP3 (up to 22 kHz sampling rate), Vorbis, and raw PCM (telephony quality, 8 kHz). The service returns audio streams sampled at 8,000 Hz, 16,000 Hz, and 22,050 Hz. Users can deliver Speech Marks using JSON containing sentence, word, viseme, and SSML elements.

Integration Scenarios

The service works with other AWS products including Amazon Lex for Voice User Interfaces and Amazon Connect for self-service contact center services. For device integration, Amazon Polly works with all available languages and voices at the highest quality, supporting reduced local resource requirements for mobile applications and IoT devices.

Supported Technologies

Amazon Polly leverages deep learning technologies and neural networks to deliver natural-sounding speech. The service supports multiple AWS regions including US East (N. Virginia), US West (Oregon), Canada (Central), Asia Pacific (Malaysia), Asia Pacific (Tokyo), Asia Pacific (Seoul), Asia Pacific (Singapore), Asia Pacific (Sydney), Africa (Cape Town), EU (London), EU (Frankfurt), EU (Ireland), and AWS GovCloud (US-West).

Development Considerations

The API accepts input as plaintext or Speech Synthesis Markup Language (SSML) format. For plaintext input, the service returns an audio stream suitable for web and mobile applications. Developers can also request PCM output format for consumption by AWS IoT devices and telephony solutions.