What is SSML? Everything to Get You Excited About SSML Wait, what is SSML? We explain SSML in simple terms, and with examples.

By Hammad Syed in API

April 7, 2024 9 min read
What is SSML? Everything to Get You Excited About SSML

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I remember discovering SSML and was super intrigued and my question, like most people who stumble upon this was “Wait, what is SSML?”

SSML stands for Speech Synthesis Markup Language. It was like discovering a secret toolkit that unlocked a whole new level of control over text to speech (TTS) technology.

So, what is SSML? Let’s dive into everything you need to know and get you excited about it. I know, I am!

So, what is SSML?

Speech Synthesis Markup Language (SSML) is essentially an XML-based markup language that gives developers the ability to customize and fine-tune text to speech voices.

Imagine being able to tweak every aspect of pronunciation, intonation, speed, and volume to tailor text to speech technology exactly how you want it. That’s what SSML offers. This is how the makers of your favorite text-to-speech-powered apps edit the speech output to sound as natural, expressive, and engaging as possible so users hear lifelike AI voices instead of robotic monotone sounds.

With SSML, I found myself able to sculpt speech output to match specific contexts and requirements, whether it’s for a virtual assistant, accessibility tool, or entertainment application, and craft an immersive user experience.

SSML vs. plain text to speech

So, you may be wondering, “How does SSML markup stack up against plain text?” While plain text to speech systems offer basic speech synthesis capabilities, SSML provides advanced control and customization options, allowing users to have finer control over the ability to specify prosody, phonetic pronunciation, and semantic interpretation resulting in more natural and contextually appropriate speech output.

Ways to use SSML

And how does one work with SSML? Well, there are a few avenues. You can dive straight into the code, embedding SSML markup directly into your application or you can take advantage of APIs provided by TTS service providers, leveraging their tools to generate speech from SSML documents. For web-based applications, embedding SSML within HTML documents seamlessly integrates rich speech capabilities.

Understanding SSML syntax

To accurately use SSML, you also have to understand its syntax. The syntax of SSML (Speech Synthesis Markup Language) is based on XML (eXtensible Markup Language), so it follows XML’s rules for structure and formatting. Here’s a breakdown of the basic syntax:

  1. Elements: SSML documents consist of nested elements, each enclosed within angle brackets (< and >). Elements can have attributes and contain text content and/or other nested elements.
  2. Tags: Tags are used to define elements. They come in pairs: an opening tag and a closing tag. The opening tag contains the element name, and the closing tag has a forward slash(/) before the element name. Example: xmlCopy code<speak> <p>This is a paragraph.</p> </speak>
  3. Attributes: Elements can have attributes, which provide additional information about the element. Attributes are specified within the opening tag and have a name-value pair format. Example: xmlCopy code<say-as interpret-as="date">2024-04-12</say-as>
  4. Text content: Elements can contain text content, which is the actual text to be spoken by the speech synthesizer. Example: xmlCopy code<p>This is a paragraph.</p>
  5. Comments: Comments can be included in SSML using <!-- to start a comment and --> to end it. Example: xmlCopy code<!-- This is a comment -->
  6. Self-closing tags: Some elements in SSML can be self-closing, meaning they don’t have a separate closing tag. Instead, the closing slash / appears at the end of the opening tag. Example: xmlCopy code<break time="500ms"/>

These are the basic elements of SSML syntax. SSML allows for a variety of elements and attributes to control various aspects of speech synthesis, such as prosody, pronunciation, and structure.

Exploring SSML elements

Now, let’s talk more about SSML elements. These are the building blocks that breathe life into synthesized speech. By using elements, I can adjust the speech output of text to speech technology and make it more lifelike. For example, I can change the speaking rate, pitch, volume, emphasis level, and more. In fact, here are some of my favorite elements and the purpose of each:

  • <break>: Adds break time or pause duration in milliseconds
  • <audio src="">: Allows for the inclusion of external audio files in the speech output (Cue the sound effects)
  • <interpret-as>: Controls how text should be interpreted, such as dates, numbers, currencies, etc.
  • <prosody>: Enables adjustment of prosodic features including pitch, rate, and volume
  • <phoneme>: Specifies the pronunciation of a word using the International Phonetic Alphabet (IPA). This one is like having my own pronunciation guide, ensuring that even the trickiest words are spoken flawlessly.
  • <voice>: Selects the voice name and language (e.g., en-us for United States English or fr for French) for speech synthesis
  • <say-as>: Specifies how text should be interpreted
  • <emphasis>: Adds emphasis to specific words or phrases
  • <lexicon>: Incorporates custom word pronunciations for words such as niche-specific jargon or unique names

Fine-tuning attributes of speech parameters

I can even use SSML to have granular control over speech synthesis parameters through attribute values like:

  • break strength: This specifies the strength of the pause in <break> elements.
  • prosody pitch: This one adjusts the pitch of the speech output.
  • prosody rate: This option controls the speaking rate of the synthesized speech.
  • prosody volume: This selection modifies the volume or loudness of the speech.
  • x-weak: This attribute indicates that the desired pronunciation or interpretation is very weak or faint. This means the text to speech technology should prioritize naturalness and fluency over accuracy.

Benefits of using SSML

In essence, SSML is the secret sauce behind truly captivating speech synthesis. With SSML in my toolkit, I can craft audio experiences that captivate and engage users like never before and you can too. Here are a few other benefits of using SSML:

  • Enhance naturalness: SSML enables fine-tuning of speech parameters for more natural-sounding output.
  • Ensure clarity: Precise pronunciation control ensures accurate rendering of complex words and phrases.
  • Improve user experience: Customized speech output enhances user engagement and satisfaction.
  • Reach a diverse audience: Developers can specify language and pronunciation rules, facilitating multilingual applications.

Common use cases for SSML

I use SSML to customize text to speech voices for a wide array of industries and scenarios. Its versatility and adaptability make it indispensable for delivering engaging and informative speech output in diverse contexts. For example, SSML can be used to create lifelike voices for:

  • Accessibility TTS: SSML can help provide audio representations of text for visually impaired users or those with reading difficulties like dyslexia.
  • Interactive voice response (IVR) systems: SSML can create interactive phone systems with natural-sounding prompts.
  • E-learning platforms: SSML can generate humanlike spoken content for educational materials.
  • Virtual assistants: SSML can enable natural and expressive interactions in virtual assistant applications like Alexa and Microsoft Cortana.

Getting started with SSML: Tips for using SSML

For developers and content creators looking to harness the power of SSML consider the following tips:

  • Start simple: Begin with basic SSML tags and gradually incorporate more advanced features.
  • Test thoroughly: Test speech output across different platforms and devices to ensure compatibility and consistency.
  • Optimize for user experience: Customize speech parameters to suit the target audience and application context.

SSML examples

I know when I first started using SSML, examples really helped me understand how to utilize it to its full potential, so let’s consider the following example of SSML:

<speak xmlns="http://www.w3.org/2001/10/synthesis" xmlns:dc="http://purl.org/dc/elements/1.1/"> <voice name="Matthew"> <prosody rate="x-slow" pitch="x-loud" volume="x-strong"> Hello, <break strength="strong"/> world. <break time="500ms"/> Welcome to the <interpret-as interpret-as="spell-out">SSML</interpret-as> tutorial. </prosody> </voice> </speak>

In this example, I selected the voice named “Matthew” and adjusted the prosody attributes to emphasize the speech. I also inserted breaks between words and sentences using <break> elements, with varying strengths and durations.

Here’s another example:

<speak> <prosody volume="x-fast">This is spoken very loudly.</prosody> <prosody volume="x-soft">This is spoken very softly.</prosody> </speak>

In this example, the <speak> element serves as the root element of the SSML document. Within it, the <prosody> element is used to modify the volume attributes of the synthesized speech. The attribute value x-fast increases the volume, resulting in loud speech, while x-soft decreases the volume, producing softer speech.

Play.HT – The most lifelike text to speech

PlayHT text to speech not only offers 900+ ultra-realistic voices across 142 languages and voice cloning but it also supports SSML, so you can meticulously fine-tune tone, pronunciation, pitch, and so much more to have the perfect voices for your project.

Ensure your AI voice overs are indistinguishable from human voices and resonate with your audience. Try PlayHT’s text to speech voice overs today at pricing you can’t beat.

What is the root element in SSML?

The root element serves as the starting point for constructing speech synthesis markup. Within this root element, developers can specify various attributes to customize the speech output to make the speech more lifelike.

Can SSML be used for controlling speech synthesis on the World Wide Web?

Yes, SSML is commonly used for controlling speech synthesis on the World Wide Web. Many web-based text to speech services and platforms support SSML for fine-tuning speech output in web applications and websites.

How does SSML help in specifying speech synthesis?

SSML allows developers to specify detailed instructions for text to speech systems, ensuring accurate pronunciation, emphasis, pauses, and other speech characteristics. This specification helps in generating more natural and expressive speech output.

Which phoneme alphabets are supported in SSML?

SSML supports various phoneme alphabets, including but not limited to:

International Phonetic Alphabet (IPA): A standardized phonetic alphabet used to represent the sounds of spoken languages.

eSpeak: A phoneme alphabet specifically designed for the eSpeak speech synthesizer, commonly used in multilingual text-to-speech applications.

Microsoft SAPI: Microsoft’s Speech Application Programming Interface includes its phoneme alphabet for specifying pronunciation in SSML.

How can I use SSML to improve voice synthesis?

With SSML, you can enhance voice synthesis by providing control over aspects such as tone, pronunciation, and pitch to achieve more natural-sounding speech.

Can SSML be used to control the speed of speech in text to speech applications?

Yes, you can use SSML to adjust the speed of speech in text to speech applications, offering flexibility in delivering content at varying rates.

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Hammad Syed

Hammad Syed

Hammad Syed holds a Bachelor of Engineering - BE, Electrical, Electronics and Communications and is one of the leading voices in the AI voice revolution. He is the co-founder and CEO of PlayHT, now known as PlayAI.

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