古琴用絃之科學鑒證

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古琴用絃之科學鑒證:
傳統真絲絃丶現代鋼絲絃丶複合絃在音調和音色上的比較 ¹
唐世璋

中國絃樂器大部份在最早時期都使用蠶絲絃，否則就多用動物腸子做絃。其後絃樂器大多數逐漸使用其他物料作絃，古琴沿用絲絃的歷史傳統，一直到了《文革》時期才起變化。在《文革》前已經有人開始研製非蠶絲的古琴絃線，原因之一是古琴絃的製作者發現難以找到高質素的蠶絲，加上彈古琴的人愈來愈少（有些人認為絲絃聲音太柔弱，難吸引人注意）。所以到了《文革》時期尼龍鋼絃便發展出新的趨向，把古琴從自我修心丶養性怡情的樂器改變為人民服務的樂器。到了八十年代，絲絃已差不多在中國消失，古琴興起，成為一種公開表演的樂器。演奏的方式，特別是在音樂學院的教授方式上，亦隨之改變。

筆者於1974年開始習琴，到90年因常被邀請公開演奏、為了在雜音多的大演奏廳中取得較佳的演奏效果，亦開始使用尼龍鋼絃，但過了一兩年後，發現常用這些絃的古琴，它的塗漆出現了剝落現象（因此珍貴的古琴只應採用真絲絃以免損壞）。

與此同時，我完成了《神奇秘譜》（1455年）所有琴曲的打譜工作，便開始發表論文討論打譜可採用的兩種方式:1.以古譜為基礎，創作新版古琴曲。2.以古譜為基礎，試圖重建古琴曲的本來面貌，而我專注採用第二種方式打譜。這樣我是試圖採用西方宗旨的所謂[復古風格演奏]的方式。根據此宗旨，學者和音樂家，一般都會根據古代曲譜，盡可能緊貼原來的譜和歷史原貌，對比相關的口述歷史和文字記載，挖掘出古代曲譜的一些原則，然後嚴僅按譜彈奏，或者按譜自由演繹（仍是依據傳統而非新版）。

[復古風格演奏]的關鍵，在於使用相關歷史時期的正確樂器，其中包括使用歷史上正確的琴絃。由於筆者使用過絲絃和鋼絃，直覺意識到不同絃，給我帶來截然不同的彈奏方式和體驗，我意識到科學鑒證的重要性，它將解答我的迷思:為何使用不同絃會產生不同的體驗。這項實驗，集中於研究絲絃和其它絃，如尼龍鋼絃和複合絃，在音調和音色上的差別。

古琴基本的一大特色是，同一個音符，用不同的方法彈奏，可以產生不同的音色；例如同一個音在不同絃上，可以彈出不同的聲音，如散音丶泛音丶按音等。這些豐富多采的音色，成為古琴之美，在傳統美學上，不可或缺的一部份。但是，我的耳朵告訴我，沒有了絲絃就沒有了這種古琴之美的豐富音色。一張古琴，當它用上尼龍鋼絃後，它無可避免地帶來不一樣的演奏方式，亦側重了與傳統古琴不一樣的音色!

這些音色的介定，最好就是聽一個音調在彈奏時所產生的倍音。現代量度音調是採用頻率，例如音樂的A調是440赫茲，即每秒440的頻率振動，但是，純粹440赫茲的聲音旣刺耳，又機械化，還有點不堪入耳!所以音調之能繞梁三日，是因為透過樂器所發出的倍音，它能夠化腐朽為神奇！這些倍音基本上以基本音為倍數比例，如2/1（880，1760…），3/2等等，當你聽到一個所謂的440赫茲的音調時，實際上是聽到了一連串倍音，總合起來，演繹為440赫茲。

我住在香港的期間，參與了一個很特別的研究:用科學方法測量不同絃樂器所產生的不同音色，目的在於能夠在一部合成器上複製出不同絃樂器的聲音。因為不同樂器所產生不同的音色，大部份都能夠憑它的倍音分辨出來，如果要在一部合成器上複製出不同絃樂器的聲音，那麽我們首先就要測量，然後再複製出這些倍音。

這項研究所測量的絃樂器，大部份為西方樂器，如結他等。我們發現，大部份絃樂器在開始彈奏時，倍音往往比基本音強很多，但很快，通常在一秒鐘之內，倍音就會消失，只餘下基本音還可以測量。

接下來，我們測量絲絃古琴，只測量其中一個音符所發出的散音丶按音丶泛音，不包括上下引和吟猱等裝飾音。我們發現，在開始彈奏時，倍音的確比基本音強很多，但它並沒有在一秒鐘之內消失，它逐漸轉弱的速度十分緩慢，而且一直保持比基本音強的狀態5秒或以上。此外，不同頻率的倍音，更以不同速度消失，因此亦令音調在轉弱時產生變幻。這樣，整體的音調似乎在細緻地波動，就像一些銅鐘被撞擊之後所發出的美妙聲音。

這項研究，解釋了傳統古琴曲目的一些特色，例如，它如何能夠在不同的絃上重複同一個音，就可以散發魅力無窮的音色。慣於操絲絃的琴人都知道，這種音色是在尼龍鋼絲絃或複合絃上找不到的。但是，據我所知，絲絃以外的其它絃，尚未充份受到科學測試。

現階段我進行的研究項目正在測量三張古琴所發出的散音丶按音丶和泛音；分別張上真絲絃丶尼龍鋼絲絃丶和複合絃的三張古琴並輪流換上不同的絃，重複測試。經過三輪試驗，將會得出三種不同絃的三張琴的不同音響結果。

目前，這個研究尚有待完成。
（2010年12月8日）

Footnotes

1. 古琴用絃之科學鑒證：
傳統真絲絃丶現代鋼絲絃丶複合絃在音調和音色上的比較
The above was translated by Stephanie Chin (錢屬賢 Qian Shuxian) from the following English article:
(Original Chinese title "古琴採用傳统真絲絃相對現代鋼絲絃和复合絃在音調和音色差別上之科學鑑證)

A scientific examination of the different tonal colors
produced on a guqin by silk, metal and composite strings
John Thompson (唐世璋)

Originally almost all Chinese stringed instruments had silk strings; those that did not usually had a form of gut. Gradually most of these stringed instruments began using other material for their strings, but it was not until the Cultural Revolution that anything other than silk was used for the strings on a guqin. Prior to the Cultural Revolution some efforts had been made to develop non-silk guqin strings. One reason was that good quality silk was not being made available to the makers of guqin strings. In addition, there seemed to be a declining interest in playing guqin, and some people blamed the quiet sounds of silk strings. Then, during the Cultural Revolution, nylon metal strings were introduced as part of an effort to change the guqin from an inward instrument of self-cultivation into an instrument that could be performed for the masses. By the 1980s silk strings were rarely used in China, epitomizing the emergence of the guqin as a performance instrument. The method of play, particularly as taught in the music conservatories, changed accordingly.

The present writer began studying guqin in 1974. Around the year 1990, as I was increasingly being asked to perform, I also began using nylon metal strings, primarily for these performances. However, within a year or two I began to notice that the constant use of these strings was causing damage to the lacquer on those instruments that had them.

In addition, having completed my reconstruction (dapu) of all the melodies in the Shen Qi Mi Pu (1425), I began presenting papers on the two approaches possible when doing dapu: using the tablature as a basis for creating new versions of old melodies, or using the tablature to try to reconstruct the music as it was played at the time it was written down. My own focus has been the latter interpretation of dapu. In this way I try to follow the principles used in the West for what is called Historically Informed Performance. According to these principles, scholars and musicians follow as closely as possible the notation and historical records of an early music genre, also examining related oral and written traditions. Then, having done as much as they can to uncover the principles behind the early music genre, they then play the music either strictly from the records of specific melodies, or freely from the tradition as learned from those records.

An essential part of Historically Informed Performance is using historically correct instruments, and this includes using the correct strings on a stringed instrument. Having used both silk and nylon metal strings I was instinctively aware of how the different types of strings changed the way I played. However, I also felt it was important to make some scientific measurements that might explain the reason for these differences. This research centers on the music colors produced by silk strings and by strings made with other materials.

One of the essential characteristics of guqin music is the fact that different colors can be achieved when playing the same pitch in different ways. Thus, any particular pitch will sound different when played as an open string, as a harmonic, or as a stopped sound on differing strings. This variety of color was an essential part of the traditional aesthetic of guqin music, but to my ears such variety of color is not possible without silk strings. Use of nylon metal strings thus leads to a different style of play, one that emphasizes other melodic possibilities on the guqin.

These musical colors can best be defined in terms of the musical overtones of the pitches being played. A musical pitch is usually defined in terms of the frequency of that pitch. Thus the modern concert A is usually defined as 440 hertz, i.e., 440 vibrations per second. However, the pure pitch 440 hz is a very piercing and mechanical sound, generally considered to be ugly. What gives beauty to the sound are the overtones that can be produced when playing this pitch on a musical instrument. These overtones are essentially multiples of the fundamental using ratios such as 2/1 (880, 1760….), 3/2 and so forth. When the ear listens to what it thinks is a pitch of 440 hz, it is actually hearing a whole series of overtones that it combines and interprets as 440 hz.

While living in Hong Kong I participated in one specific project that measured scientifically the colors produced by different stringed instruments. The aim of that project was to try to reproduce on a synthesizer the sound of various stringed instruments. Since the musical colors that distinguish different instruments can largely be described in terms of the overtones produced, reproducing their sound in a synthesizer requires measuring then reproducing these overtones.

What this research had found on all the plucked strings it had measured so far (mostly on Western instruments such as a guitar) was that when first plucked the overtones were much stronger than the fundamental. However, usually within one second most of these overtones had died away, leaving the fundamental as the main measurable pitch.

We next measured a guqin with silk strings. For this we measured open, stopped and harmonic tones, but only single notes, no slides or other ornaments. What we then discovered was that, once again, when the string was first plucked the overtones were much stronger than the fundamental. However, instead of fading away within one second, on the guqin the overtones faded very gradually, remaining stronger than the fundamental for five seconds or longer. In addition, the differing frequencies of overtones faded at different rates, and this made the sound change as it faded. Sometimes the overall pitch seemed to go slightly up and down, somewhat the way the pitch of certain bells seems to rise and fall after they have been struck.

These measurements help explain the appeal of certain characteristics of the traditional guqin repertoire, such as repeating the same note on different strings. People who regularly play with silk strings know very clearly that neither nylon-metal strings nor the new composite strings are capable of producing such varied color from repeating one note. However, to my knowledge the quality and fading of overtones for these other strings on a guqin has not yet been scientifically tested with sufficient thoroughness.

The plan of the current project is thus to measure open, stopped and harmonic sounds using three guqin. One will be strung with silk, the other with nylon-metal, the third with composite strings. The strings will then be moved onto another instrument and the test repeated. After a third such test all three types of strings will have been tested on all three instruments.

As yet, however, this testing is not yet complete.
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