Audio and Voices

Custom audio files

If custom audio files are to be used, they should preferably meet the following specification:

Other formats will be transcoded to the above.

In order to use custom audio files, they need to be available to the Voice API. This is facilitated using the Audio Manager, which allows you to upload your custom audio files onto our servers.

You are free to create any directory structure on this server, just make sure you supply the whole path from the root of your account when sending an instruction that requires an audio file.

If you want to use custom spelling audio, these files must be placed in the correct structure, as explained in the next chapter.

Custom audio files for the OTP app

In order to use custom audio files with the OTP app, you need to upload a set of audio files in the following directory structure using the Audio Manager:

/spelling/en-GB/*.wav

Where ‘en-GB’ is the language (including locale) of the set. Inside this folder, you need to upload a .wav file for every number or letter you want to be able to read aloud, like:

0.wav
1.wav
2.wav
a.wav
b.wav
c.wav

📘

For these custom audio files to work properly, please make sure that their filenames are in lowercase.

Text-To-Speech

The Voice API supports Text-To-Speech (or TTS) in all instructions where you can provide a prompt to the caller/callee. When using TTS, you can provide the voice you want to use. Currently we support the following voices:

See more supported languages https://developers.cm.com/voice/docs/supported-languages

When using TTS (or the Spelling Instruction), you can provide the voice to use in the JSON body. The voice part of the JSON body has the following variables:

C#

instruction.Voice.Language = "nl-NL";
instruction.Voice.Gender = Gender.Male;
instruction.Voice.Number = 1;
instruction.Voice.Volume = 2;

JSON

"voice": {
    "language": "nl-NL",
    "gender": "Male",
    "number": 1,
    "volume": 2,
    "premium": false
}

Variable definition

SSML

With Speech Synthesis Markup Language (SSML) you can enhance your TTS prompts. For example, you can include pause within a prompt or change the speech rate or pitch.

Example

{
    "prompt": "<speak>Hi! I will wait for 2 seconds. <break time='2s'/> Now I will spell the word hello: <break time='1s'/> <say-as interpret-as='characters'>hello</say-as>. <prosody rate='-50%' pitch='-25%' volume='+2dB'>I am speaking a bit loudly, slowly and with a lower pitch.</prosody></speak>"
}

Attributes

More advanced information about SSML and the attributes can be found in the W3C SSML Specification.