For network music performance (NMP), end-to-end delay is the most critical factor affecting the quality of experience (QoE) of the musicians, as longer delays prevent the musicians from synchronizing. To analyze the sensitivity of QoE to delay, we performed a controlled NMP experiment, where 11 pairs of musicians performed under a wide range of delays. The analysis of the QoE questionnaires answered by the participants produced results with wide variances, making the extraction of solid conclusions quite difficult. In this paper, we complement the subjective study with an analysis of the performance tempo of the NMP sessions. Specifically, we used signal processing techniques to analyze the audio recordings of the experiments, to recover the performance tempo of the musicians, assess its evolution during each session, and correlate it with the underlying delay. The results of the analysis indicate that musicians in real NMP settings are more tolerant to delay than previously thought, managing to reach and maintain a steady tempo even with one-way delays of 40 ms. We also study how the performance tempo is related to delay, finding that the exact relationship between the two depends on the musicians.
Keywords: Audio delay; NMP; QoE; Tempo.
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