3aMU8 – Comparing the Chinese erhu and the European violin using high-speed camera measurements

Florian Pfeifle – Florian.Pfeifle@uni-hamburg.de

Institute of Systematic Musicology
University of Hamburg
Neue Rabenstrasse 13
22765 Hamburg, Germany
Popular version of paper 3aMU8, “Organologic and acoustic similarities of the European violin and the Chinese erhu”
Presented Wednesday morning, November 30, 2016
172nd ASA Meeting, Honolulu

0. Overview and introduction
Have you ever wondered what a violin solo piece like Paganini’s La Campanella would sound like if played on a Chinese erhu, or how an erhu solo performance of Horse Racing, a Mongolian folk song, would sound on a modern violin?

Our work is concerned with the research of acoustic similarities and differences of these two instruments using high-speed camera measurements and piezoelectric pickups to record and quantify the motion and vibrational response of each instrument part individually.
The research question here is, where do acoustic differences between both instruments begin and what are the underlying physical mechanisms responsible?

1. The instruments
The Chinese erhu is the most popular instrument in the bowed string instrument group known as huqin in China. It plays a central role in various kinds of classical music as well as in regional folk music styles.  Figure 1 shows a handcrafted master luthier erhu.  In orchestral and ensemble music its role is comparable to the European violin as it often takes the role as the lead voice instrument.

A handcrafted master luthier erhu. This instrument is used in all of our measurements.

Figure 1. A handcrafted master luthier erhu. This instrument is used in all of our measurements.

In contrast to the violin, the erhu is played in anupright position, resting on the left thigh of the musician. It consists of two strings, as compared to four in the case of the violin. The bow is put between both strings instead of being played from the top as European bowed instruments are usually played. In addition to the difference in bowing technique, the left hand does not stop the strings on a neck but presses the firmly taut strings, thereby changing their freely vibrating length.  A similarity between both instruments is the use of a horse-hair strung bow to excite the strings.  The history of an instrument similar to the erhu is documented from the 11th century onwards, in the case of the violin from the 15th century. The historic development before that time is still not fully known, but there is some consensus between most researchers that bowed lutes have their origin in central Asia, presumably somewhere along the silk road. Early pictorial sources point to a place of origin in an area known as Transoxiana which spanned an area across modern Uzbekistan and Turkmenistan.

Comparing instruments from different cultural spheres and having different backgrounds is a many-faceted problem as there are historical, cultural, structural and musical factors playing an important role in the aesthetic perception of an instrument. Measuring and comparing acoustical features of instruments can be used to objectify this endeavour, at least to a certain degree.  Therefore, the method applied in this paper aims at finding and comparing differences and similarities on an acoustical level, using different data acquisition methods.  The measurement setup is depicted in Figure 2.

Measurement setup for both instrument measurements.

Figure 2. Measurement setup for both instrument measurements.

The vibration of the strings are recorded using a high-speed camera which is able to capture the deflection of bowed strings with a very high frame rate.  An exemplary video of such a measurement is shown in Video 1.

Video 1.  A high-speed recording of a bowed violin string.

The recorded motion of a string can now be tracked with sub-pixel accuracy using a tracking software that traces the trajectory of a defined point on the string. The motion of the bridge is measured by applying a miniature piezoelectric transducer, which converts microscopic motions into measurable electronic signals, to the bridge. We record the radiated instrument sound using a standard measurement microphone which is positioned one meter from the instrument’s main radiating part. This measurement setup results in three different types of data: first only the bowed string without the influence of the body of the instrument; the motion of the bridge and the string; and a recording of the radiated instrument sound under normal playing conditions.

Returning to the initial question, we can now analyze and compare each measurement individually. What is even more exciting, we can combine measurements of the string deflection of one instrument with the response of the other instrument’s body. In this way we can approximate the amount of influence the body has on the sound colour of the instrument and if it is possible to make an erhu performance sound like a violin performance, or vice versa. The following sound files convey an idea of this methodology by combining the string motion of part of an Mongolian folk song played on an erhu with the body of an European violin. Sound-example 1 is a microphone recording of the erhu piece and sound-example 2 is the same recording using only the string measurement combined with an European violin body.  To experience the difference clearly, headphones or reasonably good loudspeakers are recommended.

Audio File 1. A section of an erhusolo piece recorded with a microphone.

Audio File 2. A section of the same erhupiece combining the erhu string measurement with a violin body.

2. Discussion
The results clearly show that the violin body has a noticeable influence on the timbre, or quality, of the piece when compared to the microphone recording of the erhu. But even so, due to the specific tonal quality of the piece itself, it does not sound like a composition from an European tradition. This means that stylistic and expressive idiosyncrasies are easily recognizable and influence the perceived aesthetic of an instrument. The proposed technique could be used to extend the comparison of other instruments, such as plucked lutes like the guitar and pi’pa, or mandolin and ruanxian.