public Builder setCustomVoice(
        com.google.cloud.texttospeech.v1.CustomVoiceParams.Builder builderForValue) {
      if (customVoiceBuilder_ == null) {
        customVoice_ = builderForValue.build();
      } else {
        customVoiceBuilder_.setMessage(builderForValue.build());
      }
      bitField0_ |= 0x00000008;
      onChanged();
      return this;
    }
<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.v1.CustomVoiceParams custom_voice = 4;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1/src/main/java/com/google/cloud/texttospeech/v1/VoiceSelectionParams.java