public com.google.cloud.texttospeech.v1beta1.CustomVoiceParamsOrBuilder
        getCustomVoiceOrBuilder() {
      if (customVoiceBuilder_ != null) {
        return customVoiceBuilder_.getMessageOrBuilder();
      } else {
        return customVoice_ == null
            ? com.google.cloud.texttospeech.v1beta1.CustomVoiceParams.getDefaultInstance()
            : customVoice_;
      }
    }
<pre>
The configuration for a custom voice. If [CustomVoiceParams.model] is set,
the service will choose the custom voice matching the specified
configuration.
</pre>

<code>.google.cloud.texttospeech.v1beta1.CustomVoiceParams custom_voice = 4;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/VoiceSelectionParams.java