Transcribe audio with multiple channels

This page describes how to use Speech-to-Text to transcribe audio files that include more than one channel. Multi-channel recognition is available for all audio encodings supported by Speech-to-Text for up to eight channels.

If you are using AutoDetectDecodingConfig, you do not have to specify how many audio channels the file has. It's automatically determined. You must specify audio channel count when using ExplicitDecodingConfig.

Audio data usually includes a channel for each speaker present on the recording. For example, audio of two people talking over the phone might contain two channels, where each line is recorded separately.

When you send a request with multiple channels, Speech-to-Text returns a result to you that identifies the different channels present in the audio, labeling the alternatives for each result with the channel_tag field.

Before you begin

1. Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

2. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Go to project selector

3. Make sure that billing is enabled for your Google Cloud project.

4. Enable the Speech-to-Text APIs.

   Enable the APIs

5. Make sure that you have the following role or roles on the project: Cloud Speech Administrator

   Check for the roles

   1. In the Google Cloud console, go to the IAM page.

      Go to IAM
   2. Select the project.

   3. In the Principal column, find the row that has your email address.

      If your email address isn't in that column, then you do not have any roles.

   4. In the Role column for the row with your email address, check whether the list of roles includes the required roles.

   Grant the roles

   1. In the Google Cloud console, go to the IAM page.

      Go to IAM
   2. Select the project.
   3. Click person_add Grant access.
   4. In the New principals field, enter your email address.
   5. In the Select a role list, select a role.
   6. To grant additional roles, click add Add another role and add each additional role.
   7. Click Save.
6. Install the Google Cloud CLI.

7. To initialize the gcloud CLI, run the following command:

   gcloud init

8. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Go to project selector

9. Make sure that billing is enabled for your Google Cloud project.

10. Enable the Speech-to-Text APIs.

    Enable the APIs

11. Make sure that you have the following role or roles on the project: Cloud Speech Administrator

    Check for the roles

    1. In the Google Cloud console, go to the IAM page.

       Go to IAM
    2. Select the project.

    3. In the Principal column, find the row that has your email address.

       If your email address isn't in that column, then you do not have any roles.

    4. In the Role column for the row with your email address, check whether the list of roles includes the required roles.

    Grant the roles

    1. In the Google Cloud console, go to the IAM page.

       Go to IAM
    2. Select the project.
    3. Click person_add Grant access.
    4. In the New principals field, enter your email address.
    5. In the Select a role list, select a role.
    6. To grant additional roles, click add Add another role and add each additional role.
    7. Click Save.
12. Install the Google Cloud CLI.

13. To initialize the gcloud CLI, run the following command:

    gcloud init

Client libraries can use Application Default Credentials to easily authenticate with Google APIs and send requests to those APIs. With Application Default Credentials, you can test your application locally and deploy it without changing the underlying code. For more information, see Authenticate for using client libraries.

14. Create local authentication credentials for your Google Account:

    gcloud auth application-default login

Also ensure you have installed the client library.

Perform synchronous speech recognition on a multichannel file

Here is an example of performing synchronous speech recognition on a local multichannel audio file:

from google.cloud.speech_v2 import SpeechClient
from google.cloud.speech_v2.types import cloud_speech


def transcribe_multichannel_v2(
    project_id: str,
    audio_file: str,
) -> cloud_speech.RecognizeResponse:
    """Transcribe a multi-channel audio file."""
    # Instantiates a client
    client = SpeechClient()

    # Reads a file as bytes
    with open(audio_file, "rb") as f:
        content = f.read()

    config = cloud_speech.RecognitionConfig(
        auto_decoding_config=cloud_speech.AutoDetectDecodingConfig(),
        language_codes=["en-US"],
        model="long",
        features=cloud_speech.RecognitionFeatures(
            multi_channel_mode=cloud_speech.RecognitionFeatures.MultiChannelMode.SEPARATE_RECOGNITION_PER_CHANNEL,
        ),
    )

    request = cloud_speech.RecognizeRequest(
        recognizer=f"projects/{project_id}/locations/global/recognizers/_",
        config=config,
        content=content,
    )

    # Transcribes the audio into text
    response = client.recognize(request=request)

    for result in response.results:
        print(f"Transcript: {result.alternatives[0].transcript}")
        print(f"Channel tag: {result.channel_tag}")

    return response

Clean up

To avoid incurring charges to your Google Cloud account for the resources used on this page, follow these steps.

1. Optional: Revoke the authentication credentials that you created, and delete the local credential file.

   gcloud auth application-default revoke

2. Optional: Revoke credentials from the gcloud CLI.

   gcloud auth revoke

gcloud projects delete PROJECT_ID

What's next

• Practice transcribing short audio files.
• Learn how to transcribe streaming audio.
• Learn how to transcribe long audio files.
• For best performance, accuracy, and other tips, see the best practices documentation.