Transcribing phone audio with enhanced models

This tutorial shows how to transcribe the audio recorded from a phone using Speech-to-Text.

Audio files can come from many different sources. Audio data can come from a phone (like voicemail) or a soundtrack included in a video file.

Cloud Speech-to-Text can use one of several machine learning models to transcribe your audio file, to best match the original source of the audio. You can get better results from your speech transcription by specifying the source of the original audio. This allows the Cloud Speech-to-Text to process your audio files using a machine learning model trained for data similar to your audio file.


  • Send a audio transcription request for audio recorded from a phone (like voicemail) to Cloud Speech-to-Text.
  • Specify an enhanced speech recognition model for an audio transcription request.


This tutorial uses billable components of Cloud Platform, including:

  • Speech-to-Text

Use the Pricing Calculator to generate a cost estimate based on your projected usage. New Cloud Platform users might be eligible for a free trial.

Before you begin

This tutorial has several prerequisites:

Sending a request

To best transcribe audio captured on a phone, like a phone call or voicemail, you can set the model field in your <a href="/speech-to-text/docs/reference/rest/v1/RecognitionConfig"><code translate="no" dir="ltr">RecognitionConfig</code></a> payload to phone_model. The model field tells Speech-to-Text API which speech recognition model to use for the transcription request.

You can improve the results of phone audio transcription by using an enhanced model. To use an enhanced model, you set the useEnhanced field to true in your <a href="/speech-to-text/docs/reference/rest/v1/RecognitionConfig"><code translate="no" dir="ltr">RecognitionConfig</code></a> payload.

The following code samples demonstrate how to select a specific transcription model when calling Cloud Speech-to-Text.


Refer to the <a href="/speech-to-text/docs/reference/rest/v1/speech/recognize"><code translate="no" dir="ltr">speech:recognize</code></a> API endpoint for complete details.

To perform synchronous speech recognition, make a POST request and provide the appropriate request body. The following shows an example of a POST request using curl. The example uses the access token for a service account set up for the project using the Google Cloud Cloud SDK. For instructions on installing the Cloud SDK, setting up a project with a service account, and obtaining an access token, see the quickstart.

curl -s -H "Content-Type: application/json" \
    -H "Authorization: Bearer "$(gcloud auth application-default print-access-token) \ \
    --data "{
  'config': {
    'encoding': 'LINEAR16',
    'languageCode': 'en-US',
    'enableWordTimeOffsets': false,
    'enableAutomaticPunctuation': true,
    'model': 'phone_call',
    'useEnhanced': true
  'audio': {

See the <a href="/speech-to-text/docs/reference/rest/v1/RecognitionConfig"><code translate="no" dir="ltr">RecognitionConfig</code></a> reference documentation for more information on configuring the request body.

If the request is successful, the server returns a 200 OK HTTP status code and the response in JSON format:

  "results": [
      "alternatives": [
          "transcript": "Hi, I'd like to buy a Chromecast. I was wondering whether you could help me with that.",
          "confidence": 0.8930228
      "resultEndTime": "5.640s"
      "alternatives": [
          "transcript": " Certainly, which color would you like? We are blue black and red.",
          "confidence": 0.9101991
      "resultEndTime": "10.220s"
      "alternatives": [
          "transcript": " Let's go with the black one.",
          "confidence": 0.8818244
      "resultEndTime": "13.870s"
      "alternatives": [
          "transcript": " Would you like the new Chromecast Ultra model or the regular Chromecast?",
          "confidence": 0.94733626
      "resultEndTime": "18.460s"
      "alternatives": [
          "transcript": " Regular Chromecast is fine. Thank you. Okay. Sure. Would you like to ship it regular or Express?",
          "confidence": 0.9519095
      "resultEndTime": "25.930s"
      "alternatives": [
          "transcript": " Express, please.",
          "confidence": 0.9101229
      "resultEndTime": "28.260s"
      "alternatives": [
          "transcript": " Terrific. It's on the way. Thank you. Thank you very much. Bye.",
          "confidence": 0.9321616
      "resultEndTime": "34.150s"


static object SyncRecognizeEnhancedModel(string filePath)
    var speech = SpeechClient.Create();
    var response = speech.Recognize(new RecognitionConfig()
        Encoding = RecognitionConfig.Types.AudioEncoding.Linear16,
        SampleRateHertz = 8000,
        LanguageCode = "en-US",
        // Enhanced models are only available for projects that
        // opt into audio data logging.
        UseEnhanced = true,
        // A model must be specified to use an enhanced model.
        Model = "phone_call",
    }, RecognitionAudio.FromFile(filePath));
    foreach (var result in response.Results)
        foreach (var alternative in result.Alternatives)
    return 0;


func enhancedModel(w io.Writer, path string) error {
	ctx := context.Background()

	client, err := speech.NewClient(ctx)
	if err != nil {
		return fmt.Errorf("NewClient: %v", err)

	// path = "../testdata/commercial_mono.wav"
	data, err := ioutil.ReadFile(path)
	if err != nil {
		return fmt.Errorf("ReadFile: %v", err)

	resp, err := client.Recognize(ctx, &speechpb.RecognizeRequest{
		Config: &speechpb.RecognitionConfig{
			Encoding:        speechpb.RecognitionConfig_LINEAR16,
			SampleRateHertz: 8000,
			LanguageCode:    "en-US",
			UseEnhanced:     true,
			// A model must be specified to use enhanced model.
			Model: "phone_call",
		Audio: &speechpb.RecognitionAudio{
			AudioSource: &speechpb.RecognitionAudio_Content{Content: data},
	if err != nil {
		return fmt.Errorf("Recognize: %v", err)

	for i, result := range resp.Results {
		fmt.Fprintf(w, "%s\n", strings.Repeat("-", 20))
		fmt.Fprintf(w, "Result %d\n", i+1)
		for j, alternative := range result.Alternatives {
			fmt.Fprintf(w, "Alternative %d: %s\n", j+1, alternative.Transcript)
	return nil


 * Performs transcription of the given audio file synchronously with the selected model.
 * @param fileName the path to a audio file to transcribe
public static void transcribeModelSelection(String fileName) throws Exception {
  Path path = Paths.get(fileName);
  byte[] content = Files.readAllBytes(path);

  try (SpeechClient speech = SpeechClient.create()) {
    // Configure request with video media type
    RecognitionConfig recConfig =
            // encoding may either be omitted or must match the value in the file header
            // sample rate hertz may be either be omitted or must match the value in the file
            // header

    RecognitionAudio recognitionAudio =

    RecognizeResponse recognizeResponse = speech.recognize(recConfig, recognitionAudio);
    // Just print the first result here.
    SpeechRecognitionResult result = recognizeResponse.getResultsList().get(0);
    // There can be several alternative transcripts for a given chunk of speech. Just use the
    // first (most likely) one here.
    SpeechRecognitionAlternative alternative = result.getAlternativesList().get(0);
    System.out.printf("Transcript : %s\n", alternative.getTranscript());


// Imports the Google Cloud client library for Beta API
 * TODO(developer): Update client library import to use new
 * version of API when desired features become available
const speech = require('@google-cloud/speech').v1p1beta1;
const fs = require('fs');

// Creates a client
const client = new speech.SpeechClient();

 * TODO(developer): Uncomment the following lines before running the sample.
// const filename = 'Local path to audio file, e.g. /path/to/audio.raw';
// const model = 'Model to use, e.g. phone_call, video, default';
// const encoding = 'Encoding of the audio file, e.g. LINEAR16';
// const sampleRateHertz = 16000;
// const languageCode = 'BCP-47 language code, e.g. en-US';

const config = {
  encoding: encoding,
  sampleRateHertz: sampleRateHertz,
  languageCode: languageCode,
  model: model,
const audio = {
  content: fs.readFileSync(filename).toString('base64'),

const request = {
  config: config,
  audio: audio,

// Detects speech in the audio file
const [response] = await client.recognize(request);
const transcription = response.results
  .map(result => result.alternatives[0].transcript)
console.log(`Transcription: `, transcription);


def transcribe_model_selection(speech_file, model):
    """Transcribe the given audio file synchronously with
    the selected model."""
    from import speech
    client = speech.SpeechClient()

    with open(speech_file, 'rb') as audio_file:
        content =

    audio = speech.types.RecognitionAudio(content=content)

    config = speech.types.RecognitionConfig(

    response = client.recognize(config, audio)

    for i, result in enumerate(response.results):
        alternative = result.alternatives[0]
        print('-' * 20)
        print('First alternative of result {}'.format(i))
        print(u'Transcript: {}'.format(alternative.transcript))

Cleaning up

To avoid incurring charges to your Google Cloud Platform account for the resources used in this tutorial:

Deleting the project

The easiest way to eliminate billing is to delete the project that you created for the tutorial.

To delete the project:

  1. In the Cloud Console, go to the Manage resources page.

    Go to the Manage resources page

  2. In the project list, select the project you want to delete and click Delete .
  3. In the dialog, type the project ID, and then click Shut down to delete the project.

Deleting instances

To delete a Compute Engine instance:

  1. In the Cloud Console, go to the VM Instances page.

    Go to the VM Instances page

  2. Click the checkbox for the instance you want to delete.
  3. Click Delete to delete the instance.

Deleting firewall rules for the default network

To delete a firewall rule:

  1. In the Cloud Console, go to the Firewall Rules page.

    Go to the Firewall Rules page

  2. Click the checkbox for the firewall rule you want to delete.
  3. Click Delete to delete the firewall rule.