private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.texttospeech.v1.VoiceSelectionParams,
            com.google.cloud.texttospeech.v1.VoiceSelectionParams.Builder,
            com.google.cloud.texttospeech.v1.VoiceSelectionParamsOrBuilder>
        getVoiceFieldBuilder() {
      if (voiceBuilder_ == null) {
        voiceBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.texttospeech.v1.VoiceSelectionParams,
                com.google.cloud.texttospeech.v1.VoiceSelectionParams.Builder,
                com.google.cloud.texttospeech.v1.VoiceSelectionParamsOrBuilder>(
                getVoice(), getParentForChildren(), isClean());
        voice_ = null;
      }
      return voiceBuilder_;
    }
<pre>
Required. The desired voice of the synthesized audio.
</pre>

<code>
.google.cloud.texttospeech.v1.VoiceSelectionParams voice = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-texttospeech/proto-google-cloud-texttospeech-v1/src/main/java/com/google/cloud/texttospeech/v1/SynthesizeSpeechRequest.java