async function ssmlToAudio(ssmlText, outFile) {
    // Creates a client
    const client = new textToSpeech.TextToSpeechClient();

    // Constructs the request
    const request = {
      // Select the text to synthesize
      input: {ssml: ssmlText},
      // Select the language and SSML Voice Gender (optional)
      voice: {languageCode: 'en-US', ssmlGender: 'MALE'},
      // Select the type of audio encoding
      audioConfig: {audioEncoding: 'MP3'},
    };

    // Performs the Text-to-Speech request
    const [response] = await client.synthesizeSpeech(request);
    // Write the binary audio content to a local file
    const writeFile = util.promisify(fs.writeFile);
    await writeFile(outFile, response.audioContent, 'binary');
    console.log('Audio content written to file ' + outFile);
  }
Generates synthetic audio from a String of SSML text.

Given a string of SSML text and an output file name, this function
calls the Text-to-Speech API. The API returns a synthetic audio
version of the text, formatted according to the SSML commands. This
function saves the synthetic audio to the designated output file.

ARGS
ssmlText: String of tagged SSML text
outfile: String name of file under which to save audio output
RETURNS
nothing