Described is automatically testing the quality of an audio coupling between juxtaposed first and second digital telephones, e.g., VoIP telephones, such as to quantitatively determine the quality of audio echo cancellers in those digital telephones. An analyzer receives timestamps from a first telephone and second telephone during a calling session, including timestamps for when the second telephone initially provides audio (e.g., speech) to the first telephone, when the first telephone initially detects sound, when the first telephone initially provides audio to the second telephone, and when the second telephone initially detects sound. The analyzer uses the relative timing of the timestamps and the speech recognizer's outcome to determine whether the audio coupling is experiencing interference or echo. When the audio includes speech, a confidence level corresponding to accuracy of speech recognition also may establish the audio coupling's quality.