public Builder mergeVoice(com.google.cloud.texttospeech.v1beta1.VoiceSelectionParams value) {
      if (voiceBuilder_ == null) {
        if (((bitField0_ & 0x00000001) != 0)
            && voice_ != null
            && voice_
                != com.google.cloud.texttospeech.v1beta1.VoiceSelectionParams
                    .getDefaultInstance()) {
          getVoiceBuilder().mergeFrom(value);
        } else {
          voice_ = value;
        }
      } else {
        voiceBuilder_.mergeFrom(value);
      }
      if (voice_ != null) {
        bitField0_ |= 0x00000001;
        onChanged();
      }
      return this;
    }
<pre>
Required. The desired voice of the synthesized audio.
</pre>

<code>
.google.cloud.texttospeech.v1beta1.VoiceSelectionParams voice = 1 [(.google.api.field_behavior) = REQUIRED];
</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/StreamingSynthesizeConfig.java