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.
18. The receiving communication device of claim 17 , the processor and storage device storing further instructions that are operable, when executed by the processor, to perform additional operations including: receiving a synchronization signal indicating a start of the received speech, wherein determining the communication delay determines the communication delay based on receipt timing of the synchronization signal and the determination of when the speech being received ends.