sounds of the highland bagpipe

Sounds of the Highland Bagpipe

CYmL M. H^Rms

Department of Electrical Engineering, Columbia University, New York 27, New York

MAURICE EISENSTADT*

IBM Watson Laboratory, Columbia University, New York 27, New York

AND

M^•K R. Wmss

Federal Scientific Corporation, New York 27, New York (Received 3 June 1963)

An analysis has been made of the sounds of the Highland bagpipe. This instrument consists of a leather bag fitted with five pipes: the blowpipe through which the player fills the bag with air, the chanter that has eight open holes on which the melody is played, and two tenor drones and one bass drone, which produce harmonious steady tones. This study was made of the sounds produced by four individual pipers, each using his own instrument. Three of the pipers had considerable professional experience--the fourth was a young beginner. Spectral analyses were obtained for each drone and the chanter sounding separately under otherwise normal playing conditions. The harmonic structure of these sounds was investigated as a function of a number of parameters including blowing pressure, length of drone, and aging of the chanter reed. Transient as well as steady-state conditions were studied.

INTRODUCTION

HIS studv is concerned with the acoustic spectra produceci by the Highland bagpipe. This is the

familiar and popular form of the instrument that usually is associated with the term bagpipe. Figure ! shows its principal components•.2: (1) the blow pipe, a tube through which the player supplies air; (2) a leather bag, which acts as an air reservoir of moderately constant pressure; (3) the chanter, a pipe having a conical bore that is terminated in a small flange, and is excited by a double reed; and (4) the drones, jointed pipes having bores that are approximately cylindrical, each being excited by a single reed. Since no lateral holes are

* Present address: Hudson Laboratories, Columbia University. • Anthony Baines, "Bagpipes," Occasional Papers on Tech-

nology, No. 9, Pitt Rivers Museum, University of Oxford (Oxford, 1960).

2 Anthony Baines, Woodwind Instruments and Their History (W. W. Norton and Company, Inc., New York, 1963).

provided in the walls of the drones for changing their frequency, each drone emits a steady tone. It is the continuous droning sounds, which these pipes produce as an accompaniment to the melody played on the chanter, that gives the bagpipe its characteristic sound. Figure 2 is a photograph of the various reeds used in this instrument. In contrast to performers on other woodwinds, the piper has no control over the reeds and can exert little influence on the acoustic power emitted.

Although the bagpipe is one of the oldest instruments on record, there is little information concerning the detailed nature of its acoustic spectra. Here, analyses are presented of the sounds produced by each of the individual drones and by the chanter, under various playing conditions.

Several thousand spectrum analyses were obtained of the sounds produced by four pipers. Pipers designated in the following graphs by P1, P3, and P4 have had considerable professional experience;piper P2 is a young

1321

Copyright ̧ 1963 by the Acoustical Society of America.

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1322 HARRIS, EISENSTADT, AND WEISS

CHANTER - • ,

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-• BASS DRONE

MIDDLE

TENOR DRONE

Fro. 1. Photograph showing the principal components of the Highland bagpipe.

beginner. A description of their respective bagpipes follows'

P l: Pakistani drones and Granger-Campbell chanter. All reeds normal and well broken in.

P2: Henderson drones and chanter. Drone reeds

weak. Middle tenor drone inoperative. Chanter reed weak.

P3: Henderson drones and Hardie chanter. All normal and well broken in.

iP4: MacPherson drones and Hardie chanter. New

drone reeds. Chanter reed 3 months old (except where otherwise specified).

The sounds of the bagpipes were recorded using a

professional Ampex magnetic tape recorder in a sound- proof booth, approximately 10 ftX 11 ftX 10 ft high, whose walls, floor, and ceiling consisted of a sound- absorptive construction having an NRC value of 0.95. A high-quality dynamic microphone was placed at a distance of 1 m from, and the same height as, the chanter or from the drone being recorded with the bagpipe in normal playing position. Consideration was given to the directional properties of the instrument. Because the open ends of the pipes are small compared with the wavelengths of most of the significant components of the sounds that are radiated, the sounds of the bagpipes are relatively nondirectional. Measure- ments showed that the average acoustic power output

Fro. 2. Photograph showing a chanter reed tenor drone reed, and bass drone reed.

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20:48:04

SOUNDS OF THE H5I•GHLAND BAGPIPE 1323

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FREQUENCY IN KC/SEC

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Fxo. 3. Photograph showing Fourier analyses of sounds produced by a middle tenor drone of piper P1 during the initial buildup of air pressure in the bag. The lowest frame illustrates a normal spectrum. (Only the first 5 kc/sec of the analyses is shown here.)

of'this instrument is about 10 to 20 mW under normal playing conditions.

Spectral analyses then were made of the recorded data by means of a SIMOR^mC analyzer, employing the system described by Weiss and Harris? This analyzer, of the correlation type, has a resolution of 63 cps over an 8-kc/sec range. It provides continuous Fourier analyses in real time at discrete processing intervals that can be selected arbitrarily. Most of the results presented here employed a processing time of 24 msec, although some transient phenomena were studied with a processing time of 12 msec. Typical results of the output of the analyzer are illustrated in Fig. 3. This sequence of traces was photographed with a motion picture camera, employing an oscilloscope having a very short persist- ence on which the analysis was displayed. It shows the spectra of sounds produced by the middle tenor drone during the initial buildup of air pressure. At a particular pressure, the vibration of the reed changes from one mode to another. The change is characterized by a slight change in frequency and a change in quality. This phenomenon is known to pipers as the "double tone." The second mode is the normal playing condition for the drone. Figure 3 shows the transition between modes; the upper trace shows the first mode, and the bottom trace shows the normal conditions.

I. DRONES

Figure 4 shows a detailed cross section of typical tenor and bass drones, which consist of two and three jointed sections, respectively. (The drones, as well as the chanter, usually are made of African blackwood.) This arrangement permits the drone's length to be varied, thereby affecting the fundamental frequency that it produces. Each drone contains a single me- chanical (beating-type) reed made of cane. The reed sound of this type usually is rich in harmonics. 4 The drones are adjusted to proper length by ear so that the fundamental frequency of the bass drone is two octaves below the A produced by the chanter, and the fundamental frequency of each of the tenor drones is one octave below chanter A. More pronounced changes in fundamental frequency can be made by moving the bridle, a tight-fitting cord on the reed that determines the length of the vibrating tongue (see Fig. 2). Such a change also affects the spectrum of the sound produced by the drone.

The results of typical spectra produced by the bass

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Fro. 4. Cross-section drawing showing details of construction of the drones. The numerical values represent dimensions expressed in inches. The letter D following a number signifies that this number is the diameter of the drone at the point indicated.

3 M. R. Weiss and C. M. Harris, J. Acoust. Soc. Am. 35, 207-214 4 T. F. S. Harris, Handbook of Acoustics (J. Curwen & Sons Ltd, (1963). London, 1913), Chap. 10.


20:48:04


F 2 4 6 8 I0 12 14 16 18 20 22 24 26 HARMONIC NUMBER

any other two middle tenor drones or any other two outer tenor drones. This would indicate that the physi- cal characteristics of the drones are a more dominant

influence than the drone reeds.

The sound-pressure level at a distance of 1 m from any of the drones, sounding alone, is in the range of 70 to 77 dB, depending on the reed and the setting of the bridle.

Influence of Drone Length

Since the drones are adjustable in length, several tests were made to see how this change in dimension affects the spectrum of a tenor drone. Normal blowing pressure was maintained. These results are summarized in Fig. 7. The spectrum shown in the middle was ob-

Fro. 5. Spectra of the sounds produced by bass drones for piper P1, P2, P3, and P4. Relative sound pressure is plotted against harmonic number. The fundamental frequency is approximately 115 cps.

drones are illustrated in Fig. 5 for the four pipers. These data were obtained with the pipers blowing at what may be described as "normal" blowing pressure. Note that these spectra are rich in both odd and even harmonics.

Similar data for the tenor drones are presented in Fig. 6. It is interesting to note that the spectra of the middle and outer tenor drones of one bagpipe resemble each other much more closely than do the spectra of

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FIG. 6. Spectra of the sounds produced by the outer :enor (signified by the dashed lines, OT) and middle (signified by the solid lines, MT) drones for pipers P1, P2, P3, and P4. Relative sound pressure is plotted against harmonic number. The fundamental frequency is approximately 230 cps.

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Fro. 7. Spectra of the acoustic output of the middle tenor drone of piper P4 when adjusted to three lengths. Relative sound pressure is plotted as a function of harmonic number. The fundamental frequency is indicated on each graph.

tained with the length of the drone adjusted to a typical value; the upper spectrum was obtained with the drone adjusted to its shortest operative position; the lower spectrum was obtained with the drone adjusted to its longest operative position. Beyond these extreme posi- tions, the drone reed would not vibrate. Thoughout this series of tests, the position of the bridle on the drone reed was not moved. The resulting data indicate that the length to which a drone is adjusted is a significant parameter in determining the acoustic spectrum that it produces.

II. CHANTERS

The chanter pipe contains eight lateral holes. By fingering these holes, a melody of nine notes can be


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Fie. 8. Schematic diagram showing the important dimensions of a modern chanter whose bore (shown on the right) consists of three truncated cones. The numerical values represent dimensions expressed in inches. The letter D following a number signifies that this number is the diameter of the hole in the wall at the point indicated. The wall thickness at the uppermost hole is 0.25 in.; it is 0.18 in. at the two vent holes at the base (0.365 D); it is 0.20 in. at all other holes.

played, from low G to high A. A drawing showing a cross section of the chanter is given in Fig. 8. Figure 9 shows the results of measurements of the spectra of four chanters blown under normal conditions. (For purposes of comparison, an envelope was drawn for the spectra of the chanter of piper ?4.) A comparison of the formant structure of the pitch harmonics from one note to another indicates that there is a peak in acoustic output in the region of 2 kc/sec.

Measurements of the fundamental frequencies of the chanter notes were made for the four pipers. The results were in close agreement with, but about l% higher in frequency than, the results of Lenihan and MacNeill 5

5 j. M. A. Lenihan and S. MacNeill, Acustica 4, 231-232 (1954).

for the chanter scale. The value they obtained for A was 459 cps. At a distance of i m from the chanter (for piper P4), the sound-pressure levels for the notes were as follows:

G, 92 dB; A, 91 dB; B, 89 dB; C, 90 dB; D, 88 dB; E, 88 dB; F, 90 dB; G, 83 dB; A, 82 dB.

These measurements were made with the microphone placed along the axis of the chanter.

Effect of Aging on a Reed

Two sets of data are shown in Fig. 9 for one piper-- the first, designated at P4a, was taken 3 months before

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FIG. 9. Spectra of the acoustic output of the chanters of pipers P1-P4 for notes from low G to high A. Relative sound pressure is plotted for the various harmonics. The points P4a were taken when the chanter reed was almost new. The points P4b were taken about 3 months later when the reed was somewhat more seasoned.



F 2 4 6 8 I0 12 14 HARMONIC NUMBER

Fro. 10. Spectra of the acoustic output of chanter A for several values of air pressure in the bag. Relative sound pressure is plotted in each graph as a function of harmonic number. The fundamental frequency here depends on the air pressure and is approximately 465 cps. The air pressure, indicated on each graph, is expressed in cm of water.

the data designated as P4b. In the interim, the chanter reed received considerable use. It is well known among woodwind players that reeds change in quality during their lifetime, particularly when relatively new. Initi- ally, they tend to sound louder and more harsh. When the reeds age, they are said to sound mellower. An ex- planation for this change is given by a comparison of the spectra over the three-month period for P4. Initially, a high-frequency formant is very much in evidence. With age, this high-frequency formant is suppressed, reducing the loudness and resulting in a spectrum that one can apparently describe as being mellower.

Chanter A vs Blowing Pressure

An experiment was carried out in which the air pressure in the bag could be measured by means of a manometer. Then the acoustic spectral analyses for the chanter were made for various blowing pressures. These data are presented in Fig. 10 for tone A (approximately 460 cps). The air pressures indicated in this illustration are manometer readings expressed in centimeters of water. The range shown represents the practical limits of operating air pressure. Below the lower limit, the chanter reed fails to vibrate. To main- tain an air pressure higher than the upper limit would require lungs of extraordinary power. From the lowest value of pressure to the highest value, the over-all sound-pressure level at a distance of 1 m increases by about 4 dB. For typical blowing conditions, the air

pressure in the bag corresponds to a manometer reading of approximately 75 cm of water.

False Notes vs True Notes

Hypothetically, a chanter could be designed so that one of the following methods of fingering can be used to ascend the scale: (1) by lifting the fingers from the holes in sequence from all closed to all open, or (2) by lifting only one finger at a timemone for each note. Actually, the chanter is designed so that under normal conditions a method is used which is intermediate be-

tween the first and second techniques. An experiment was conducted in which the spectra of the true notes (produced by normal fingering) were compared with spectra of notes produced by the first of the above methods of fingering. The latter notes are referred to here as "false" notes. While the spectra for comparable true and false notes were not the same, the differences in harmonic structure were not regarded as significant. For the lower notes, there were some differences in the fundamental frequencies of the two types of notes; furthermore, the sound-pressure level was greater for the false notes. This increase in acoustic output may be a result of radiation of acoustic energy by the holes.

Transient Conditions

Figure 11 shows a series of five consecutive spectra which represent Fourier analyses at 24-msec intervals. They are reproduced from a motion picture film taken of the oscilloscopic display of the output of the analyzer. First, a steady state was established for the tone B on the chanter. This spectrum is shown in the upper two

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Fro. 11. Photograph showing Fourier analyses taken at 24-msec intervals during the playing of two notes on the chanter. The upper two spectra were taken during the playing of chanter B. The lower two spectra were taken during the playing of chanter C. In the spectrum shown in the center, one can see evidence of the decay of the initial sound and the buildup of the subsequent sound.


SOUNDS OF THE HIGHLAND BAGPIPE 1327

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TIME IN MILLISECONDS

Fro. 12. Photograph showing the sound-pressure amplitude as a function of time in the transition region in going from E to low A on the chanter.

frames. Next, the fingering was changed from B to C. The resulting spectrum during the processing period cor- responding to this transition is shown in the center frame. The lower two frames show the spectrum for C. A detailed examination of such records indicates that

less than 24 msec (the processing period used here) is required to establish a steady-state condition in going from one note to another.

It is of interest to observe the time function of the

sound pressure for sounds of the chanter. Such records were obtained by photographing the face of a cathode- ray oscilloscope in which the spot remained in a fixed position in the horizontal direction, but the vertical

deflection was proportional to over-all sound pressure. The face of the screen then was photographed with a motion picture camera in which the film traveled 10 in./sec. Figure 12 shows a typical pressure-time function so obtained during the transition from chanter E to A. Examination of time functions such as these

reveals the following observation. If one follows the envelope of the time function, then immediately after the change to the new note takes place (the change is denoted by the vertical arrow on the left), the amplitude of the time function increases to a value that is higher than it is during the subsequent steady state for the new note; finally, steady state is reached. The maximum amplitude of the envelope is indicated by the vertical arrow on the right. Observe that only a few complete cycles are required to achieve a steady-state condition. During the entire transition, the acoustic output is continuous.

ACKNOWLEDGMENTS

The authors wish to acknowledge the kind coopera- tion of the following pipers' Pipe Major Joseph Brady, J. W. Burgess, and William Barr.


sounds of the highland bagpipe

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