*For German voices,* indicates how the service is to spell out strings of individual letters.
To indicate the pace of the spelling, specify one of the following values: * `default` - The
service reads the characters at the rate at which it synthesizes speech for the request. You
can also omit the parameter entirely to achieve the default behavior. * `singles` - The service
reads the characters one at a time, with a brief pause between each character. * `pairs` - The
service reads the characters two at a time, with a brief pause between each pair. * `triples` -
The service reads the characters three at a time, with a brief pause between each triplet.
For more information, see [Specifying how strings are spelled
out](https://cloud.ibm.com/docs/text-to-speech?topic=text-to-speech-synthesis-params#params-spell-out-mode).