How to use the microphone-stream.toRaw function in microphone-stream

function convertAudioToBinaryMessage(audioChunk) {
    let raw = mic.toRaw(audioChunk);

    if (raw == null)
        return;

    // downsample and convert the raw audio bytes to PCM
    let downsampledBuffer = audioUtils.downsampleBuffer(raw, sampleRate);
    let pcmEncodedBuffer = audioUtils.pcmEncode(downsampledBuffer);

    // add the right JSON headers and structure to the message
    let audioEventMessage = getAudioEventMessage(Buffer.from(pcmEncodedBuffer));

    //convert the JSON object + headers into a binary event stream message
    let binary = eventStreamMarshaller.marshall(audioEventMessage);

    return binary;
}

startMic.on('data', (chunk) => {
          var raw = mic.toRaw(chunk);
          if (raw == null) {
            return;
          }

        buffer = buffer.concat(...raw)
        this.setState({audioBuffer: buffer})
      });