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

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.

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

Go to project selector

Verify that billing is enabled for your Google Cloud project .

Enable the Speech-to-Text APIs.

Enable the APIs

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 all rows that identify you or a group that you're included in. To learn which groups you're included in, contact your administrator.

4. For all rows that specify or include you, check the Role column to see 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 user identifier. This is typically the email address for a Google Account.

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 .

Install the Google Cloud CLI.

If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity .

To initialize the gcloud CLI, run the following command:

gcloud  
init

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

Go to project selector

Verify that billing is enabled for your Google Cloud project .

Enable the Speech-to-Text APIs.

Enable the APIs

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 all rows that identify you or a group that you're included in. To learn which groups you're included in, contact your administrator.

4. For all rows that specify or include you, check the Role column to see 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 user identifier. This is typically the email address for a Google Account.

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 .

Install the Google Cloud CLI.

If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity .

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 .

1. If you're using a local shell, then create local authentication credentials for your user account:

   gcloud  
   auth  
   application-default  
   login

   You don't need to do this if you're using Cloud Shell.

   If an authentication error is returned, and you are using an external identity provider (IdP), confirm that you have signed in to the gcloud CLI with your federated identity .

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:

  import 
  
 os 
 from 
  
 google.cloud.speech_v2 
  
 import 
 SpeechClient 
 from 
  
 google.cloud.speech_v2.types 
  
 import 
 cloud_speech 
 PROJECT_ID 
 = 
 os 
 . 
 environ 
 [ 
 "GOOGLE_CLOUD_PROJECT" 
 ] 
 def 
  
 transcribe_multichannel_v2 
 ( 
 audio_file 
 : 
 str 
 , 
 ) 
 - 
> cloud_speech 
 . 
 RecognizeResponse 
 : 
  
 """Transcribe the given audio file synchronously with multichannel. 
 Args: 
 audio_file (str): Path to the local audio file to be transcribed. 
 Example: "resources/two_channel_16k.wav" 
 Returns: 
 cloud_speech.RecognizeResponse: The full response object which includes the transcription results. 
 """ 
 # Instantiates a client 
 client 
 = 
 SpeechClient 
 () 
 # Reads a file as bytes 
 with 
 open 
 ( 
 audio_file 
 , 
 "rb" 
 ) 
 as 
 f 
 : 
 audio_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 
 = 
 audio_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

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.