public Builder clearAudioTopic() {
      audioTopic_ = getDefaultInstance().getAudioTopic();
      bitField0_ = (bitField0_ & ~0x00000080);
      onChanged();
      return this;
    }
<pre>
Description of the content. Eg. "Recordings of federal supreme court
hearings from 2012".
</pre>

<code>string audio_topic = 10;</code>

@return This builder for chaining.
java-speech/proto-google-cloud-speech-v1/src/main/java/com/google/cloud/speech/v1/RecognitionMetadata.java