Research

St. Lawrence String Quartet

Different experiments have been made with the help of the St. Lawrence String Quartet (SLSQ), Stanford University's Ensemble-in-Residence. We present here a test that was done between CCRMA and the Banff Centre for the Arts at Alberta, Canada (June 2006). The quartet was located at Banff and was extended by a viola player performing from CCRMA, forming a displaced string quintet. The setup was done in such a way that only the room acoustics of the hall at Banff were heard . In order to achieve this effect, the viola player was placed in an semi-anechoic room. Four speakers were positioned simulating the physical locations of the other members of the quintet (violin 1, violin 2, viola 1, violoncello) surrounding the viola performer. Each of these instruments was picked up using a directional microphone that was fed into the individual speakers in the semi-anechoic room, forming the quintet on the Stanford side. Two extra microphones where used to capture the acoustics of the hall. Two MS pair microphones were utilized for the viola player at Stanford and sent to a pair of speakers at Banff, forming the quintet on that end.

During this test, the audio RTT (round trip time) was approx. 50 ms . Neglecting any asymmetries, the performers where separated by a path of approx. 25 ms (unidirectional). They performed standard classical repertoire (Mozart's String Quintet in G minor, K. 516).

Reactions to the delay

NOTE: All the audio files were recorded at Banff.

Qualitative analysis of the performance, recordings and comments from the musicians serve to illustrate some of the important topics on this discussion.

During a section between the viola (Stanford) and the violoncello (Banff) which constituted a rhythmic unison, the performance naturally slowed down:
SLSQretard1.mp3

This was a predicted effect. Interestingly though, when used consciously by the musicians, it led to what was called the perfect ritard. The effect of "viola waits for cello" and "cello waits for viola" led to this controlled ritardando, down to a certain point where the tempo stabilized.
SLSQretard2.mp3

The amount of delay, duration of attack, and the fact that this part of the performance included only two instruments (i.e., in "power" equilibrium) can explain this phenomenon. The musicians were also able to maintain the tempo when done consciously, i.e., when they were aware of the delay effect, they could define strategies to be able to play on time (without ritard):
SLSQstable_duo.mp3

All these effects where observed when there was an equal balance in "ensemble power" with only two musicians performing.

Another interesting effect observed dealt with the opposite situation; an unbalanced power between the two groups. Since four musicians were at Banff and just one at Stanford, the natural tendency (or strategy) of the Stanford viola player was just to follow the quintet. The quartet at Banff had to compensate and "struggle" for with the additional delay coming in from Stanford. This struggling was clearly heard during the test; at one moment, the performers in Banff asked to "turn off" the viola (speaker) coming from Stanford. In that case, what was heard at Stanfod was an impeccable performance. This is a real-time case of music minus one:
SLSQstable_quintet.mp3

With the the viola player's audio shut down, its signal was recorded dry, without the room reverberation. This, plus the fact that now the quartet at Banff was not struggling against it, made the effect the asynchronization much more evident. This suggests the following:

• When there is an unbalance in power (e.g., more musicians or rhythmic domination in one location than the other), the "weak" side has an important effect in balancing the performance and in the overall delay compensation.
• Reverberation has (almost certainly) a positive contribution on the perception of synchronization, and can be used to advantage , either acoustically or virtually.