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Train a custom speech model

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In this article, you learn how to train a custom model to improve recognition accuracy from the Microsoft base model. The speech recognition accuracy and quality of a custom speech model remains consistent, even when a new base model is released.

Note

You pay for custom speech model usage and endpoint hosting. You'll also be charged for custom speech model training if the base model was created on October 1, 2023 and later. You are not charged for training if the base model was created prior to October 2023. For more information, see Azure AI Speech pricing and the Charge for adaptation section in the speech to text 3.2 migration guide.

Training a model is typically an iterative process. You first select a base model that is the starting point for a new model. You train a model with datasets that can include text and audio, and then you test. If the recognition quality or accuracy doesn't meet your requirements, you can create a new model with more or modified training data, and then test again.

You can use a custom model for a limited time after it was trained. You must periodically recreate and adapt your custom model from the latest base model to take advantage of the improved accuracy and quality. For more information, see Model and endpoint lifecycle.

Important

If you will train a custom model with audio data, choose a Speech resource region with dedicated hardware for training audio data. After a model is trained, you can copy it to a Speech resource in another region as needed.

In regions with dedicated hardware for custom speech training, the Speech service will use up to 100 hours of your audio training data, and can process about 10 hours of data per day. See footnotes in the regions table for more information.

Create a model

After you upload training datasets, follow these instructions to start training your model:

  1. Sign in to the Speech Studio.

  2. Select Custom speech > Your project name > Train custom models.

  3. Select Train a new model.

  4. On the Select a baseline model page, select a base model, and then select Next. If you aren't sure, select the most recent model from the top of the list. The name of the base model corresponds to the date when it was released in YYYYMMDD format. The customization capabilities of the base model are listed in parenthesis after the model name in Speech Studio.

    Important

    Take note of the Expiration for adaptation date. This is the last date that you can use the base model for training. For more information, see Model and endpoint lifecycle.

  5. On the Choose data page, select one or more datasets that you want to use for training. If there aren't any datasets available, cancel the setup, and then go to the Speech datasets menu to upload datasets.

  6. Enter a name and description for your custom model, and then select Next.

  7. Optionally, check the Add test in the next step box. If you skip this step, you can run the same tests later. For more information, see Test recognition quality and Test model quantitatively.

  8. Select Save and close to kick off the build for your custom model.

  9. Return to the Train custom models page.

    Important

    Take note of the Expiration date. This is the last date that you can use your custom model for speech recognition. For more information, see Model and endpoint lifecycle.

To create a model with datasets for training, use the spx csr model create command. Construct the request parameters according to the following instructions:

  • Set the project parameter to the ID of an existing project. This parameter is recommended so that you can also view and manage the model in Speech Studio. You can run the spx csr project list command to get available projects.
  • Set the required dataset parameter to the ID of a dataset that you want used for training. To specify multiple datasets, set the datasets (plural) parameter and separate the IDs with a semicolon.
  • Set the required language parameter. The dataset locale must match the locale of the project. The locale can't be changed later. The Speech CLI language parameter corresponds to the locale property in the JSON request and response.
  • Set the required name parameter. This parameter is the name that is displayed in the Speech Studio. The Speech CLI name parameter corresponds to the displayName property in the JSON request and response.
  • Optionally, you can set the base property. For example: --base 5988d691-0893-472c-851e-8e36a0fe7aaf. If you don't specify the base, the default base model for the locale is used. The Speech CLI base parameter corresponds to the baseModel property in the JSON request and response.

Here's an example Speech CLI command that creates a model with datasets for training:

spx csr model create --api-version v3.2 --project YourProjectId --name "My Model" --description "My Model Description" --dataset YourDatasetId --language "en-US"

Note

In this example, the base isn't set, so the default base model for the locale is used. The base model URI is returned in the response.

You should receive a response body in the following format:

{
  "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd",
  "baseModel": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/base/5988d691-0893-472c-851e-8e36a0fe7aaf"
  },
  "datasets": [
    {
      "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/datasets/23b6554d-21f9-4df1-89cb-f84510ac8d23"
    }
  ],
  "links": {
    "manifest": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd/manifest",
    "copy": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd:copy",
    "files": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd/files"
  },
  "project": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/projects/0198f569-cc11-4099-a0e8-9d55bc3d0c52"
  },
  "properties": {
    "deprecationDates": {
      "transcriptionDateTime": "2026-07-15T00:00:00Z"
    },
    "customModelWeightPercent": 30,
    "features": {
      "supportsTranscriptions": true,
      "supportsEndpoints": true,
      "supportsTranscriptionsOnSpeechContainers": false,
      "supportedOutputFormats": [
        "Display",
        "Lexical"
      ]
    }
  },
  "lastActionDateTime": "2024-07-14T21:38:40Z",
  "status": "Running",
  "createdDateTime": "2024-07-14T21:38:40Z",
  "locale": "en-US",
  "displayName": "My Model",
  "description": "My Model Description"
}

Important

Take note of the date in the adaptationDateTime property. This is the last date that you can use the base model for training. For more information, see Model and endpoint lifecycle.

Take note of the date in the transcriptionDateTime property. This is the last date that you can use your custom model for speech recognition. For more information, see Model and endpoint lifecycle.

The top-level self property in the response body is the model's URI. Use this URI to get details about the model's project, manifest, and deprecation dates. You also use this URI to update or delete a model.

For Speech CLI help with models, run the following command:

spx help csr model

To create a model with datasets for training, use the Models_Create operation of the Speech to text REST API. Construct the request body according to the following instructions:

  • Set the project property to the URI of an existing project. This property is recommended so that you can also view and manage the model in Speech Studio. You can make a Projects_List request to get available projects.
  • Set the required datasets property to the URI of the datasets that you want used for training.
  • Set the required locale property. The model locale must match the locale of the project and base model. The locale can't be changed later.
  • Set the required displayName property. This property is the name that is displayed in the Speech Studio.
  • Optionally, you can set the baseModel property. For example: "baseModel": {"self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/base/5988d691-0893-472c-851e-8e36a0fe7aaf"}. If you don't specify the baseModel, the default base model for the locale is used.

Make an HTTP POST request using the URI as shown in the following example. Replace YourSubscriptionKey with your Speech resource key, replace YourServiceRegion with your Speech resource region, and set the request body properties as previously described.

curl -v -X POST -H "Ocp-Apim-Subscription-Key: YourSubscriptionKey" -H "Content-Type: application/json" -d '{
  "project": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/projects/0198f569-cc11-4099-a0e8-9d55bc3d0c52"
  },
  "displayName": "My Model",
  "description": "My Model Description",
  "baseModel": null,
  "datasets": [
    {
      "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/datasets/23b6554d-21f9-4df1-89cb-f84510ac8d23"
    }
  ],
  "locale": "en-US"
}'  "https://YourServiceRegion.api.cognitive.microsoft.com/speechtotext/v3.2/models"

Note

In this example, the baseModel isn't set, so the default base model for the locale is used. The base model URI is returned in the response.

You should receive a response body in the following format:

{
  "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd",
  "baseModel": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/base/5988d691-0893-472c-851e-8e36a0fe7aaf"
  },
  "datasets": [
    {
      "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/datasets/23b6554d-21f9-4df1-89cb-f84510ac8d23"
    }
  ],
  "links": {
    "manifest": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd/manifest",
    "copy": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd:copy",
    "files": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9e240dc1-3d2d-4ac9-98ec-1be05ba0e9dd/files"
  },
  "project": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/projects/0198f569-cc11-4099-a0e8-9d55bc3d0c52"
  },
  "properties": {
    "deprecationDates": {
      "transcriptionDateTime": "2026-07-15T00:00:00Z"
    },
    "customModelWeightPercent": 30,
    "features": {
      "supportsTranscriptions": true,
      "supportsEndpoints": true,
      "supportsTranscriptionsOnSpeechContainers": false,
      "supportedOutputFormats": [
        "Display",
        "Lexical"
      ]
    }
  },
  "lastActionDateTime": "2024-07-14T21:38:40Z",
  "status": "Running",
  "createdDateTime": "2024-07-14T21:38:40Z",
  "locale": "en-US",
  "displayName": "My Model",
  "description": "My Model Description"
}

Important

Take note of the date in the adaptationDateTime property. This is the last date that you can use the base model for training. For more information, see Model and endpoint lifecycle.

Take note of the date in the transcriptionDateTime property. This is the last date that you can use your custom model for speech recognition. For more information, see Model and endpoint lifecycle.

The top-level self property in the response body is the model's URI. Use this URI to get details about the model's project, manifest, and deprecation dates. You also use this URI to update or delete the model.

Copy a model

You can copy a model to another project that uses the same locale. For example, after a model is trained with audio data in a region with dedicated hardware for training, you can copy it to a Speech resource in another region as needed.

Follow these instructions to copy a model to a project in another region:

  1. Sign in to the Speech Studio.
  2. Select Custom speech > Your project name > Train custom models.
  3. Select Copy to.
  4. On the Copy speech model page, select a target region where you want to copy the model. Screenshot of a phrase list applied in Speech Studio.
  5. Select a Speech resource in the target region, or create a new Speech resource.
  6. Select a project where you want to copy the model, or create a new project.
  7. Select Copy.

After the model is successfully copied, you'll be notified and can view it in the target project.

Copying a model directly to a project in another region isn't supported with the Speech CLI. You can copy a model to a project in another region using the Speech Studio or Speech to text REST API.

To copy a model to another Speech resource, use the Models_Copy operation of the Speech to text REST API. Construct the request body according to the following instructions:

  • Set the required targetSubscriptionKey property to the key of the destination Speech resource.

Make an HTTP POST request using the URI as shown in the following example. Use the region and URI of the model you want to copy from. Replace YourModelId with the model ID, replace YourSubscriptionKey with your Speech resource key, replace YourServiceRegion with your Speech resource region, and set the request body properties as previously described.

curl -v -X POST -H "Ocp-Apim-Subscription-Key: YourSubscriptionKey" -H "Content-Type: application/json" -d '{
  "targetSubscriptionKey": "ModelDestinationSpeechResourceKey"
} '  "https://YourServiceRegion.api.cognitive.microsoft.com/speechtotext/v3.2/models/YourModelId:copy"

Note

Only the targetSubscriptionKey property in the request body has information about the destination Speech resource.

You should receive a response body in the following format:

{
  "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9df35ddb-edf9-4e91-8d1a-576d09aabdae",
  "baseModel": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/base/eb5450a7-3ca2-461a-b2d7-ddbb3ad96540"
  },
  "links": {
    "manifest": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9df35ddb-edf9-4e91-8d1a-576d09aabdae/manifest",
    "copy": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/models/9df35ddb-edf9-4e91-8d1a-576d09aabdae:copy"
  },
  "properties": {
    "deprecationDates": {
      "adaptationDateTime": "2023-01-15T00:00:00Z",
      "transcriptionDateTime": "2024-07-15T00:00:00Z"
    }
  },
  "lastActionDateTime": "2022-05-22T23:15:27Z",
  "status": "NotStarted",
  "createdDateTime": "2022-05-22T23:15:27Z",
  "locale": "en-US",
  "displayName": "My Model",
  "description": "My Model Description",
  "customProperties": {
    "PortalAPIVersion": "3",
    "Purpose": "",
    "VadKind": "None",
    "ModelClass": "None",
    "UsesHalide": "False",
    "IsDynamicGrammarSupported": "False"
  }
}

Connect a model

Models might have been copied from one project using the Speech CLI or REST API, without being connected to another project. Connecting a model is a matter of updating the model with a reference to the project.

If you're prompted in Speech Studio, you can connect them by selecting the Connect button.

Screenshot of the connect training page that shows models that can be connected to the current project.

To connect a model to a project, use the spx csr model update command. Construct the request parameters according to the following instructions:

  • Set the project parameter to the URI of an existing project. This parameter is recommended so that you can also view and manage the model in Speech Studio. You can run the spx csr project list command to get available projects.
  • Set the required modelId parameter to the ID of the model that you want to connect to the project.

Here's an example Speech CLI command that connects a model to a project:

spx csr model update --api-version v3.2 --model YourModelId --project YourProjectId

You should receive a response body in the following format:

{
  "project": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/projects/0198f569-cc11-4099-a0e8-9d55bc3d0c52"
  },
}

For Speech CLI help with models, run the following command:

spx help csr model

To connect a new model to a project of the Speech resource where the model was copied, use the Models_Update operation of the Speech to text REST API. Construct the request body according to the following instructions:

  • Set the required project property to the URI of an existing project. This property is recommended so that you can also view and manage the model in Speech Studio. You can make a Projects_List request to get available projects.

Make an HTTP PATCH request using the URI as shown in the following example. Use the URI of the new model. You can get the new model ID from the self property of the Models_Copy response body. Replace YourSubscriptionKey with your Speech resource key, replace YourServiceRegion with your Speech resource region, and set the request body properties as previously described.

curl -v -X PATCH -H "Ocp-Apim-Subscription-Key: YourSubscriptionKey" -H "Content-Type: application/json" -d '{
  "project": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/projects/0198f569-cc11-4099-a0e8-9d55bc3d0c52"
  },
}'  "https://YourServiceRegion.api.cognitive.microsoft.com/speechtotext/v3.2/models"

You should receive a response body in the following format:

{
  "project": {
    "self": "https://eastus.api.cognitive.microsoft.com/speechtotext/v3.2/projects/0198f569-cc11-4099-a0e8-9d55bc3d0c52"
  },
}

Next steps