private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.texttospeech.v1beta1.AudioConfig,
            com.google.cloud.texttospeech.v1beta1.AudioConfig.Builder,
            com.google.cloud.texttospeech.v1beta1.AudioConfigOrBuilder>
        getAudioConfigFieldBuilder() {
      if (audioConfigBuilder_ == null) {
        audioConfigBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.texttospeech.v1beta1.AudioConfig,
                com.google.cloud.texttospeech.v1beta1.AudioConfig.Builder,
                com.google.cloud.texttospeech.v1beta1.AudioConfigOrBuilder>(
                getAudioConfig(), getParentForChildren(), isClean());
        audioConfig_ = null;
      }
      return audioConfigBuilder_;
    }
<pre>
Required. The configuration of the synthesized audio.
</pre>

<code>
.google.cloud.texttospeech.v1beta1.AudioConfig audio_config = 3 [(.google.api.field_behavior) = REQUIRED];
</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/SynthesizeLongAudioRequest.java