# Impact of Audio Delay and Quality in Network Music Performance +
## 2 Related Work  
A large amount of research considers the QoE for NMP, evaluating it from diverse points of view. An overview of such research can be found in [PERSON] et al. (2018). The most common approach is to manipulate a parameter (such as delay) over a set of NMP sessions and subjectively evaluate the resulting QoE via questionnaires; we adopt the same approach. [PERSON] (2018) investigated the effect of latency on musical synchronization and introduced the concept of the Ensemble Performance Threshold (EPT), defined as the one-way delay below which synchronization remains achievable. The study set this threshold to 20-30 ms. [PERSON] (2018), through hand-clapping experiments with musicians, found a similar EPT, also noting that latencies below 11 ms could lead to tempo acceleration. [PERSON] (2018) examined two musicians performing hand claps without a metronome and reported that increasing delay caused a gradual slowdown in tempo. [PERSON] (2018) expanded on this by studying eleven musically trained pairs trying to synchronize their hand claps, finding a linear relationship between delay and tempo reduction. [PERSON] (2018) also investigated the relationship between latency and tempo, using seventeen pairs of hand clapping participants. The study revealed that 74% of performances sped up when the delay was below 11.5 ms, whereas 85% of sessions with delays above 14 ms experienced a tempo slowdown. [PERSON] (2018) conducted experiments with four musicians playing bass, percussion, piano, and guitar, concluding that all participants tolerated higher delay values when playing at slower tempos, regardless of their instrumental skills or instrument type. In a follow-up study, [PERSON] (2018) examined the influence of note attack time on tempo. Using cello and violin performances, the study found that pieces with fast attack times generally maintained a higher tempo, but in both fast and slow attack conditions, tempo decreased with increased delay. [PERSON] (2018) further explored how delay interacts with musical content, involving seven pairs of musicians in varying settings of latency, jitter, tempo, and instrumental combinations. The study reported that perceived delay was strongly affected by the rhythmic and timbral characteristics of the instruments, with noisier or more rhythmically complex combinations being more sensitive to delay. These findings highlight that the enjoyability and feasibility of NMP are not determined by latency alone but also by the musical context. [PERSON] (2018) examined ten professional musicians, five drummers and five bassists, performing in pairs. The study reported an overall latency threshold ranging from 5 ms to 65 ms, with no single acceptance value across all participants, emphasizing the subjective variability in latency tolerance. [PERSON] (2018) studied a conductor with six singers performing together over a network. Despite the technical limitations, singers were generally able to adapt to various delay levels and reported forming emotional connections with each other. [PERSON] (2018) asked two pairs of musicians to perform [PERSON] duets under different latency conditions. While the musicians employed various coping strategies, they noted that delays of 100 ms or more made performances feel unmusical and non-interactive, leading them to rely more on self-monitoring than on active listening. [PERSON] [16] investigated the subjective experience of ten participants playing instruments such as mandolin, accordion, guitar, percussion, harp, flute, and alto saxophone in duos. The study confirmed that latency negatively affected musical involvement and caused noticeable distress among musicians. However, participants also showed a willingness to find coping mechanisms to mitigate the disruptive effects of delay. Collectively, the hand clapping studies indicate that when delay exceeds 30 ms, synchronization fails.