Voice speed

Because of the natural variation between voices, each available voice speaks at slightly different speeds. For instance, with US English voices, Ivy and Joanna are slightly faster than Matthew, and considerably faster than Joey. Since there is so much variation between voices, there is no standard speed (words per minute) available for Amazon Polly voices. However, you can find how long it takes for your voice to say the selected text using Speech Marks.

To time the length of a spoken text passage

1. Open the AWS CLI.

2. Run the following code, filling in as needed.

        aws polly synthesize-speech \
             --language-code optional language code if needed
             --output-format json \
             --voice-id [name of desired voice] \
             --text '[desired text]' \
             --speech-mark-types='["viseme"]' \
             LengthOfText.txt

3. Open LengthOfText.txt.

If the text were "Mary had a little lamb," the last few lines returned by Amazon Polly would be:

     {"time":882,"type":"viseme","value":"t"}
     {"time":964,"type":"viseme","value":"a"}
     {"time":1082,"type":"viseme","value":"p"}

The last viseme, essentially the sound for the final letters in "lamb" starts 1082 milliseconds after the beginning of the speech. While this is not exactly the length of the audio, it's close and can serve as the basis for comparison between voices.

Changing your voice speed

For certain applications, you may find that you'd prefer the voice you like be slowed down, or speeded up. If the speed of the voice is a concern, Amazon Polly provides the ability to modify this using SSML tags. For example, if your organization was making an application that reads books to immigrant audiences, you may want to vary the voice speed. Your audience may speak English, but their fluency is limited. Amazon Polly helps you slow down the rate of speech using the SSML <prosody> tag.

You can use a percentage:

<speak>
     In some cases, it might help your audience to <prosody rate="85%">slow 
     the speaking rate slightly to aid in comprehension.</prosody>
</speak>

Or a preset speed:

<speak>
     In some cases, it might help your audience to <prosody rate="slow">slow 
     the speaking rate slightly to aid in comprehension.</prosody>
</speak>

Two speed options are available to you when using SSML with Amazon Polly:

• Preset speeds: x-slow, slow, medium, fast, and x-fast. In these cases, the speed of each option is approximate, depending on your preferred voice. The medium option is the normal speed of the voice.

• n% of speech rate: any percentage of the speech rate, between 20% and 200% can be used. In these cases, you can choose exactly the speed you want. However, the actual speed of the voice is approximate, depending on the voice you've chosen. 100% is considered to be the normal speed of the voice.

Note

Test your selected voice at various speeds. The speed of each option is approximate and depends on the voice you choose.

For more information on using the prosody tag, see Controlling volume, speaking rate, and pitch .