17. A receiving communication device to evaluate audio quality of a real-time communication received from a transmitting communication device via a real-time communication system, the receiving communication device comprising: a processor and a non-transitory storage device storing instructions that are operable, when executed by the processor, to cause the processor to perform operations including: receiving an audio signal, the audio signal including speech; receiving a reference script containing linguistic contents in text form, of the speech included in the audio signal, wherein the reference script excludes audio; receiving an expected duration of the speech in the audio signal; enabling a voice activity detector according to the expected duration of the speech in the audio signal; detecting when the speech being received ends using the voice activity detector; determining a communication delay based on the when expected duration and the determination of when the speech being received ends; generating an evaluation transcript in text form by applying speech recognition to the speech in the received audio signal; comparing the reference script with the evaluation transcript; and generating a call quality metric of the real-time communication system based on the comparison.
19. The receiving communication device according to claim 17 , wherein the audio signal containing speech is generated by a text-to-speech process based on the reference script.