Quantum Physics Offers Insights into Expressivity of Music

Vibrato is the up-down movement in pitch introduced during vocal or instrumental performance, intended to supplement expressivity and to boost sound projections, and popularly used in opera. A beautifully and well-timed executed vibrato can greatly improve the quality of sound of a note, and induce robust emotional responses in the listener.

This is the use of Filter Diagonalisation Method or FDM in music signal processing. This method has origins in quantum physics and is employed to research molecular dynamics and nuclear magnetic resonance.

“We are now a step closer to comprehending the mechanics of music communication, the nuances that performers present to the music, and the logic behind them,” says co-author and project supervisor Lecturer Elaine Chew from the Centre for Digital Music at the QMUL’s School of Electrical Engineering and Computer Science.

The method’s potential to identify and estimate properties from very fine silvers of information comes in specifically handy in vibrato analysis and enables scientists to analyse music signals with bigger accuracy than before.

Vibratos usually move at a rate of 4 to 8 cycles per second, or with a period of 125 – 250 milliseconds per cycle. The extent to which the pitch is bent down or up can be up to half a semitone. Since vibrations occur so quickly, standard methods need a comparatively big window for analysing the music signal have so far struggled to precisely capture their properties.

“The FDM algorithm was primarily introduced to effectively and efficiently explore the intricate quantum dynamical resonances of molecules and atoms. Although music signals are very distinct from their quantum counterparts, mathematically they share numerous similarities, comprising the properties of their resonances,” says Dr Khalid Rajab, project co-supervisor and co-author of QMUL’s School of Computer Science and Electrical Engineering.

“In fact, we have identified that since they move with time, the harmonics in musical signals can be more intricate to analyse than their quantum counterparts,” he confirms. The study emerged from a project to model the dissimilarities between playing an erhu and a violin, a two-stringed Chinese fiddle.

Lecturer Chew says, “When music for a folk instrument such as the erhu is performed on a violin, it lacks the stylistic and expressive qualities of the original. One of the primary sources of such differences lies in the way in which notes are elaborated and the way in which the instrumentalists make their alterations between notes.

Yang, and avid erhu player says, “In erhu, as in violin playing, vibrato is frequently employed to mimic the liveliness and colourful expressivity of the human voice.

Conclusion

The scientists expect the novel method will aid musicians and music teachers in their quest to accomplish the perfect vibrato, assist sound artists in preparing more natural sounding vibrato effects in audio production, and allow scientists to map trends in vibrato use across time and cultures