PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Study on the evaluation index of the tonal noise components
generated from small fan
Takefumi NAKANO1; Gaku MINORIKAWA2
1

Hosei University, Japan

2

Hosei University, Japan

ABSTRACT
There are various cooling methods, but small fans are generally used in order to cool information equipment
such as personal computers, projectors and others. The noise generated from small fans contains tonalcomponents, which are mainly caused by the flow temporal variation, the motor’s electromagnetic force andothers. It's known that these tonal components contribute to not only the overall sound pressure level but also
the harsh sound. Although several indices for evaluating tonal components have been proposed, it cannot be
said that these are able to be evaluated small fans appropriately. In this study, the new evaluation indices havebeen proposed. These are named Total Tone-to-Noise Ratio and Total Prominence Ratio based on tonalcomponents evaluation indices Tone-to-Noise Ratio and Prominence Ratio defined in the annex such as
ECMA-74. These evaluation indices are total values of TNR or PR of each tonal component included in thenoise. Therefore, it is possible to evaluate multiple tonal components individually or comprehensively. In ourprevious study, it has been confirmed that these new indices are effective for subjective annoyance in small
axial fan or small centrifugal fan. This study is attempted to determine their subjective evaluation thresholdswith the sensory test.
Keywords: Small fan, Fan noise, Tonal components evaluation

1. INTRODUCTION
In recent years, the information technology equipment such as personal computers, projectors andothers have become as necessities for modern life. The amount of heat generated due to highintegration of electronic components is increasing along with the high performance or miniaturizationof these equipment. Although there are various methods of cooling, the small fans that are very
efficient and low-cost are generally used in order to cool them. The noise reduction of the small fan
advances and A-weighted sound pressure level itself is kept low, but even that slight sound may be felt
annoying in a quiet living environment.
As for the influence of tonal components on the sense of hearing, the evaluation indices called
Tone-to-Noise Ratio (hereinafter, referred to as TNR) and Prominence Ratio (hereinafter, referred toas PR) are defined in such as ISO 7779 (1), ECMA-74 (2) and ANSIS 1.13 (3). These are theevaluation indices for evaluating individual tonal components contained in noise and are not theevaluation indices for overall evaluating multiple tonal components contained in noise. Therefore, wehave proposed the new indices called Total Tone-to-Noise Ratio (hereinafter, referred to as T-TNR)
and Total Prominence Ratio (hereinafter, referred to as T-PR) for evaluating the noise in which
multiple tonal components are contained. On the other hand, the psychoacoustic approach to detect the
tonal feeling has been also developed and the index such as Tonality has been used for the evaluationof the overall tonal feeling.
The effectiveness of T-TNR and T-PR for annoying was verified with the sensory test by soundsources processed a small axial fan noise and a small centrifugal fan noise or sound sources
synthesized white noise and sine wave by Minorikawa et al. (4, 5). The previous study concluded
that T-TNR and T-PR could be used as a simple calculation procedure to evaluate noise with multiple
1
2

takefumi.nakano.8z@stu.hosei.ac.jp
minori@hosei.ac.jp8055

tonal components and could be effective as a method to evaluate tonal components when there was
not enough deviation in Tonality. However, it was the relative result obtained by the paired
comparison method, the absolute threshold level of T-TNR or T-PR has not been obtained yet.
The purpose of this study is to determine the threshold levels which has not been determined in
the previous study for annoyance in T-TNR or T-PR with the sensory test (the method of adjustment)by sound sources processed small axial fan noises. Furthermore, the effectiveness of the determinedthreshold levels is verified with actual small fan noises.

2. NOISE CHARACTERRISTICS OF SMALL FAN
2.1 Mechanism of fan noise generation
The noise generated from fan includes the aerodynamic noise that temporal fluctuation of flow
becomes sound source, the mechanical noise that mechanical vibration becomes sound source, theelectromagnetic noise that electromagnetic force fluctuation of motor becomes sound source andothers. Among them, the aerodynamic noise is dominant in the operating state of a normal fan and it
can be classified into the rotational noise and the turbulent flow noise from its sound source
characteristics. In fan noise, it is known that the noise including high tonal components is felt moreannoyance even if the overall level is the same. (6)The rotational noise is generated by periodic pressure fluctuations accompanying the passage of theimpeller. In the case of a centrifugal fan, it has tonal components on the product of the number of
blades and the number of rotations and on their harmonics. In the case of an axial fan, it has tonalcomponents on the product of the number of rotor blades and the number of rotations and on theirharmonics. It becomes very annoying sound because it has high contribution to the overall of
A-weighted sound pressure level. Therefore, it is firstly important to reduce the rotational noise formeasures of fan noise. This noise is caused by two types of unsteady flow. One is called the potential
interference noise caused by the pressure distribution around the impeller and the other is called wakeinterference noise induced by the separated flow from the trailing edge of the impeller. In case of thesmall axial fan, the unsteady flow interfere the obstacles and large noise is generated, when the
obstacles such as stators and spokes are located just behind the impeller. (6)The turbulent noise is caused by the random turbulent flow generated by the fan. The noise source
consists of the pressure fluctuations induced by the turbulent boundary layer on the surface of theimpeller, the fluctuation of lift caused by the vortex shedding from the trailing edge of the impell er andso on. It has broadband frequency components, though the energy is smaller than the rotational noise
energy and the contribution to the overall of A-weighted sound pressure level is secondary.In fan
noise, the noise with high tonal components is more annoying even if the overall of A-weighted soundpressure level is the same. (6)2.2 Tonal components of axial fan
The rotational noise from axial fans is caused by the interference between the periodic f low fromthe impeller and the stator or the spoke which supports the motor. The frequencies of tonal components
are shown as the following formula:f r ,iwhere,
݅݊i  Z r  n (Hz): order of harmonics ( i 1,2,3,…): rotational speed per second

ܼ௥

(1)

: number of rotor blades

2.3 Tonal components of centrifugal fan
The rotational noise from centrifugal fans is caused by the interference between the periodic flowfrom the impeller blade and the tongue of the fan casing. The frequencies of tonal components areshown as the following formula:f r ,i i  Z r  n (Hz)(2)
where,
݅: order of harmonics ( i 1,2,3,…)
ܼ௥: number of blades݊: rotational speed per second

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3. EVALUATION METHODS OF TONAL COMPONENTS
3.1 Tone-to-Noise Ratio and Prominence Ratio
In general, the prominence of a tonal component is determined by the physical relationships
between the tonal component level and the surrounding band noise level which is masking the tonalcomponent. The frequency band of the surrounding is so called the critical band that is centered at thefrequency of the tone. In the existing standards such as the ISO 7779 (1), ECMA-74 (2) and ANSI
S1.13 (3), the evaluation methods of the certain prominent discrete tone in information technology
equipment are prescribed as TNR and PR, in the very similar manners. In this study, th e methods ofAnnex D of ECMA 74 were referred for determining TNR and PR of each tonal component of interest.
The TNR (ο‫ ) ் ܮ‬is defined as the decibel value of the ratio of the power of tonal component andother noise component in the critical band. In ECMA-74, when TNR exceeds by 8 dB at 1 kHz or
higher, the tonal component is classified as prominent discrete tone. In case that multiple peaks exist in
the same critical band or the noise levels adjacent to the critical band is considerable, TNR vales tends
to show bigger or smaller. (2)
'LT

§W ·
10 log10 ¨¨ t ¸¸ (dB)
© Wn ¹(3)where,'LT : tone-to-noise ratio according to ECMA-74 (dB): power of tone (Pa 2 )Wn : power of other components in critical band (Pa 2)
The PR (ο‫ܮ‬௉ ) is defined as the decibel value of the ratio of the critical band power including the
tonal component and the average of the adjacent critical band power on both sides. In ECMA-74, when
PR exceeds by 9 dB at 1 kHz or higher, the tonal component is classified as prominent discrete tone.
Figure 1 is the schematic view of calculating TNR and PR. (2)
Wt

'LP

ª
º
WM
10 log10 «» (dB)¬ WL  WU 2 ¼

(4)

'LP

: prominence ratio according to ECMA-74 (dB)

WM

: power of middle critical band (Pa 2 )WL: power of lower critical band (Pa2)

WU: power of upper critical band (Pa2)

40

40

30

30

Sound Pressure Level (dB)

Sound Pressure Level (dB)

where,

20
10
0

-10

20
10

0
-10

100

200

300
Frequency (Hz)

400

500

100

200

300
Frequency (Hz)

400

500

Figure 1 – Schematic view of TNR and PR calculation (Left: TNR, Right: PR)
3.2 Total Tone-to-Noise Ratio and Tonal Prominence Ratio
In fan noise evaluation, it is important to identify and quantify the tonal components for the productquality control, the detection of noise source and the noise reduction. In Tonality, the method of
calculation is a little bit complicated and it is difficult to identify which tonal components have highcontribution. On the other hand, TNR and PR can be the indicators for the prominent discrete tone of8057

each tonal component. However, they still don’t consider relationship between the multiple tonalcomponents.
In this study, the new evaluation parameters called T-TNR and T-PR have been proceed. The
individual levels of TNRs or PRs are determined for each of multiple tonal components in the noise
spectrum of interest, by the calculation methods of TNR or PR, and the power summation thereof isdefined as an evaluation parameter as T-TNR or T-PR, respectively. Figure 2 is the schematic view of
calculating T-TNR and T-PR.

LT

§ n
·
10 log10 ¨ 10'LTi 10 ¸
¨
¸
©i 1
¹

¦

(5)

LP

§ n
·
10 log10 ¨ 10'LPi 10 ¸
¨
¸
©i 1
¹

(6)

¦

where,: T-TNR (dB)LP

'LPi : prominence ratio for i-th tonal component (dB)
: T-PR (dB): number of tonal components of the noise spectrum of interest

n
40

40

30

30

Sound Pressure Level (dB)

Sound Pressure Level (dB)'LTi : tone-to-noise ratio for i-th tonal component (dB)

LT

20
10

0
-10

20
10

0
-10

100

300

500
Frequency (Hz)

700

900

100

300

500
Frequency (Hz)

700

900

Figure 2 – Schematic view of T-TNR and T-PR calculation (Left: T-TNR, Right: T-PR)
3.3 Tonality
Tonality, T is widely known as the indices that indicate the tonal perception of the sound. This index
is provided by such as Terhardt and Aures (7, 8). It is calculated as the product of the various weighted
functions to the tonal components such as the influence of masking by other tones, the ratio of tonalcomponents and noise, the influence of hearing threshold and is applicable to the evaluation ofsubjective tonality for the object sound.
3.4 The threshold level for subjective annoyance of T-TNR or T-PR
In order to evaluate whether the fan noise is good or bad, it is necessary to determine the boundary
level of T-TNR and T-PR which is felt or is not felt to be annoyance subjectively, that is, the thresholdlevel. In this study, T-TNR or T-PR threshold levels are determined by a commercially available small
axial fan noise as a reference sound source. The threshold levels for the subjective annoyance of
T-TNR and T-PR are newly defined as ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴ in this study.

4. SENSORY TEST
4.1 Test fans
In this study, seven types of small axial fans are prepared as base sound sources for sensory test andsound sources for threshold level verification. The test fans with a blade diameter of 80 mm, a rated
speed of 2000 rpm and the number of blades of seven blades are adopted as a reference fan, the8058different blade diameter fan (Only Fan E is blade diameter of 120 mm.) and the different rated speedfans (Fan F and Fan G are rated speed of 2800 rpm.) are also targeted.
The sound sources of test fans were recorded in the hemi-anechoic room in our university. The fanswere driven the approximately rated speed without flow restriction and the sound sources were
measured with the precision noise level meter (RION NL-31) set at 500 mm apart from the front of thesuction side of them. The sound sources were stored as WAV files to the computer via themulti-channel signal analyzer (RION SA-01). The sampling frequency at the recording was 51.2 kHz
and the recording time was about 10 seconds.
The characteristics of each test fan obtained from the recorded data are shown on Table 1. In thecalculation of T-TNR and T-PR, the tonal components up to the seventh order caused by rotational
noise are considered.
Table 1 – Characteristics of test fans‫ܮۃ‬୘ ‫ۄ‬,‫ۄ ୔ܮۃ‬,Loudness,

Sharpness,

Overall level,

dB

dB

sone

acum

dB

Fan A

5.4

9.5

1.1

1.5

30.7

Fan B

9.7

11.5

0.7

1.2

27.0

Fan C

3.1

9.6

0.3

1.5

22.5

Fan D

3.6

8.7

0.9

1.4

29.0

Fan E

12.0

13.9

2.9

1.5

38.9

Fan F

19.4

16.5

2.1

1.3

36.1

Fan G

6.5

12.8

1.3

1.4

31.3

5.8

2.8

0.9

0.1

5.5

Fan NameStandard
deviation

4.2 Test sounds
The test sounds adopt the sounds which are removed the blade passing frequency components fromthe sound sources of the recorded test fans as the reference sound sources. At the sensory test, it isdecided to add together the tonal components up to the seventh order to these reference sound sources
and adjust their levels. In addition, the change rate of every tonal component is determined based on
the level at the rated speed. At the sensory test, the test sound based on the reference sound source of
Fan A is named "Sound A" and the same applies to the test sounds of other fans.
4.3 Method of adjustment
The method of adjustment is used as the sensory test method in this study. The method ofadjustment is a method in which the experimenter or the jury freely changes a stimulus to ob tain thevalue of the stimulus which gives a specific sensation. This method is characterized by relatively
taking little trouble, efficient measurement and less influence of subject's operation error compared toother test methods. (9, 10)
The implementation method of the sensory test by the method of adjustment is as follows. First ofall, the juries hear only the reference sound source and adjust its level and then they decide thethreshold level of the reference sound source at which they start feeling annoyance. Next, the juries
hear the sound added together the seven tonal components to the reference sound source and adjust its
level and then they decide the threshold level of the sound at which they start feeling annoyance. This
test carries out for all of seven sound sources. The order of the sound sources presented to the juries are
random and both ascending series and descending series are carried out in consideration of theinfluence of the systematic error. Although the strict time limit for judging one sound is not set, alljuries are provided instructions so as not to spend too much time for one sound before the test. And thejuries are 16 college students (from 20 to 25 years old) who have the normal hearing ability and wereselected at random. Incidentally, this test is performed by the application that is created for thesensory test of the method of adjustment.

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5. RESULT AND DISCUSSION
5.1 The threshold levels for every test soundThe threshold levels for each test sound and standard deviations are shown on Table 2. However,the numbers shown in parentheses are for the standard deviations of test sounds. Also, the correlation
coefficients of indices are shown on Table 3.
The standard deviations of Loudness and Sharpness have been small and the standard deviations of‫ܮۃ‬୘ ‫ۄ‬଴, ‫ۄ ୔ܮۃ‬଴ and Overall levels have been largish. That is, since the threshold values of Loudness andSharpness have had small dispersion, it is considered that they tend to be good as the threshold levels.
However, as shown on Table 1, since the standard deviation of Sharpness in fan noise is also small, it
might be difficult to use only Sharpness as an evaluation index for the annoyance. About the otherindices, since the standard deviations of the threshold levels and the standar d deviations of the fannoises have been secured, it is considered that there is a possibility that one or a combination of themcan be used as the evaluation indices.According to Table 3, it has been confirmed that ‫ܮۃ‬୘ ‫ۄ‬଴ or‫ۄ ୔ܮۃ‬଴ and Sharpness had a high negative correlation. On the other hand, it has been confirmed that‫ܮۃ‬୘ ‫ۄ‬଴ or ‫ۄ ୔ܮۃ‬଴ and Overall levels are not as large as the correlation coefficient with Sharpness, buthave positive correlation. Also, the correlation coefficient between ‫ۄ ୔ܮۃ‬଴ and Loudness has beensmall. Thus, it has been confirmed that ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴ , which have a high correlation with
Sharpness that is stable as a threshold level, are effective as an evaluation index of annoyance.
Table 2 – Threshold levels for every test sound‫ܮۃ‬୘ ‫ۄ‬଴,‫ۄ ୔ܮۃ‬଴,

Loudness,

Sharpness,

Overall level,

dB

dB

sone

acum

dB

Sound A

12.5 (6.8)

13.9 (5.1)

1.9 (1.4)

1.2 (0.3)

33.8 (7.5)

Sound B

17.9 (8.4)

20.3 (7.1)

2.4 (1.7)

1.0 (0.3)

37.0 (6.9)

Sound C

16.3 (6.3)

16.6 (5.3)

2.1 (1.1)

1.2 (0.3)

34.7 (5.7)

Sound D12.5 (5.3)

14.3 (4.0)

1.5 (1.1)

1.3 (0.2)

31.8 (6.7)

Sound E

20.3 (7.1)

24.0 (6.8)

2.2 (1.8)

1.1 (0.3)

34.9 (6.9)

Sound F19.0 (7.5)

24.5 (6.9)

1.8 (1.2)

1.1 (0.3)

35.1 (6.6)

Sound G

13.2 (6.0)

15.4 (4.3)

2.1 (1.8)

1.3 (0.3)

33.3 (8.4)

3.3

4.5

0.3

0.1

1.6

Test Sound

Standard
deviation

Table 3– Correlation coefficients for every test sound‫ܮۃ‬୘ ‫ۄ‬଴‫ۄ ୔ܮۃ‬଴

Loudness

Sharpness

Overall level‫ܮۃ‬୘ ‫ۄ‬଴

---

0.96

0.51

-0.83

0.74

‫ۄ ୔ܮۃ‬଴

0.96

---

0.33

-0.81

0.64

Loudness

0.51

0.33

---

-0.55

0.80

Sharpness

-0.83

-0.81

-0.55

---

-0.89

Overall Level

0.74

0.64

0.80

-0.89

---

5.2 The threshold levels for every jury
The standard deviations of every jury are shown on Table 4 and the correlation coefficients areshown on Table 5.
The standard deviations of Loudness and Sharpness have been small, while the standard deviationsof ‫ܮۃ‬୘ ‫ۄ‬଴ or ‫ۄ ୔ܮۃ‬଴ and Overall level have been largish. The standard deviations have tended to belarger in all indices as compared with the results for every test sounds. It is considered that this isaffected by the difference in individual tolerance range with respect to the presentation test sounds.
In addition, when these correlation coefficients are compared with the results for every test sounds,

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the sign of the correlation coefficients between ‫ܮۃ‬୘ ‫ۄ‬଴ or ‫ۄ ୔ܮۃ‬଴ and Loudness or Sharpness have been
inverted. On the other hand, it has been confirmed that the correlation coefficient with Sharpness has
a high negative correlation like the result for every test sou nds. Thus, as the evaluation results forevery jury, the threshold levels ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴ tend to decrease as Loudness, Sharpness and Overalllevel increase. It might say that this is a logical result.
Table 4 – Standard deviation for every jury

Standard
deviation‫ܮۃ‬୘ ‫ۄ‬଴,‫ۄ ୔ܮۃ‬଴,

Loudness,

Sharpness,

Overall level,

dB

dB

sone

acum

dB

4.6

4.5

1.3

0.3

6.2

Table 5 – Correlation coefficients for every jury‫ܮۃ‬୘ ‫ۄ‬଴‫ۄ ୔ܮۃ‬଴

Loudness

Sharpness

Overall level‫ܮۃ‬୘ ‫ۄ‬଴

---

0.97

-0.59

-0.90

-0.45

‫ۄ ୔ܮۃ‬଴

0.97

---

-0.53

-0.87

-0.35

Loudness

-0.59

-0.53

---

0.78

0.94

Sharpness

-0.90

-0.87

0.78

---

0.74

Overall Level

-0.45

-0.35

0.94

0.74

---

5.3 Threshold levels and their evaluation
The results for every test sound are adopted as the threshold levels and are shown on Table 6. The
results of applying these threshold levels to the test fan noises are shown on Figure 4.
Since TNR and PR have a complementary relationship, when the test fan noise exceeding boththreshold levels is regarded as NG, all the test fans have prepared this time are evaluated as OK.
However, in my opinion, this evaluation results does not seem to be in line with the auditory
impression. Therefore, the test fan noises have been re-evaluated with Overall level that obtained asa result of frequency analysis as an additional evaluation parameter. In this case, the calculation for
Loudness is not required. The results are shown on Figure 5. If the test fan above both ‫ܮۃ‬୘ ‫ۄ‬଴ or‫ۄ ୔ܮۃ‬଴ and the approximate curve (linear approximation) of Overall level is regarded as NG, Fan E
and Fan F of the test fans are evaluated as NG. On Figure 4, when the evaluation level is evaluatedas “Threshold level − Standard deviation”, it can be confirmed that the similar trend is obtained.
Thus, it is considered that it is necessary to improve the accuracy of the threshold levels by
increasing the number of subjects or examining a data organization method.
Table 6 – The threshold levels of T-TNR and T-PR

Threshold Level‫ܮۃ‬୘ ‫ۄ‬଴,dB‫ۄ ୔ܮۃ‬଴, dB

15.9

18.4

30

30
<LT>0

25

<LT>0

<LT>0-σ

20

20

T-PR (dB)T-TNR (dB)

<LT>0-σ

25

15

15

10

10

5

5

0

0

Fan A Fan B Fan C Fan D Fan E Fan F Fan G

Fan A Fan B Fan C Fan D Fan E Fan F Fan G

Figure 4 – Evaluation of the threshold levels

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50

50

Fan E

Fan F
Overall Level (dB)Overall Level (dB)

Fan E
40

30

20

40

Fan F

30

20

Threshold levels for test sounds

Threshold levels for test sounds

Test fans

Test fans

10

10
0

5

10

15
T-TNR (dB)

20

25

30

0

5

10

15
T-PR (dB)

20

25

30

Figure 5 – Relationships between T-TNR or T-PR and Overall levels

6. SUMMARY
In this study, the threshold levels of T-TNR and T-PR which are new evaluation indices of noise
including multiple tonal components have been determined with the sensory test.
1. The analysis results for every test sound have confirmed that ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴ have a negative
correlation with Sharpness. On the other hand, the correlation between ‫ۄ ୔ܮۃ‬଴ and Loudness has notbeen not high. The threshold levels are 15.9 dB for ‫ܮۃ‬୘ ‫ۄ‬଴ and 18.4 dB for ‫ۄ ୔ܮۃ‬଴.
2. The analysis results for every jury have confirmed that ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴ have a negative correlation
with Sharpness. On the other hand, the correlations between ‫ܮۃ‬୘ ‫ۄ‬଴ or ‫ۄ ୔ܮۃ‬଴ and Overall level havenot been high.
3. As the results of evaluating the test fan noises with the threshold levels ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴ which are
obtained, it is considered that it might be possible to evaluate the annoyance with an approximation
curve (linear approximation) of ‫ܮۃ‬୘ ‫ۄ‬଴ or ‫ۄ ୔ܮۃ‬଴ and Overall level. Also, since these trends arealmost the same as the result of evaluating the threshold level as "Threshold level -Standard
deviation". In future, we would like to improve the accuracies of threshold levels ‫ܮۃ‬୘ ‫ۄ‬଴ and ‫ۄ ୔ܮۃ‬଴.

ACKNOWLEDGEMENTS
Special thanks goes to Small Fan Workshop members for them valuable suggestions.

REFERENCES
1. ISO 7779 3rd edition, Acoustics – Measurement of airborne noise emitted by information technology
and telecommunications equipment, International Organization for Standardization, 2010.
2. ECMA-74 12th edition, Measurement of Airborne Noise emitted by Information Technology and
Telecommunications Equipment, Ecma International, 2012.
3. ANSI S1.13 5th Edition, American National Standard Measurement of Sound Pressure Levels in Air,American National Standards Institute, 2005.
4. Gaku Minorikawa, Takao Yamaguchi, Masayuki Kihara, STUDY ON EVALUATION METHOD OFTONAL NOISE FOR SMALL FAN, Proceedings of ICSV22, 2015.
5. Takefumi Nakano, Gaku Minorikawa, STUDY ON EVALUATION METHOD OF THE TONALNOISE COMPONENTS FOR SMALL FAN, Proceedings of ICSV25, 2018.
6. Shoji Suzuki, Masaharu Nishimura, Shinya Kijimoto and Gaku Minorikawa, Mechanical AcousticalEngineering, Corona publishing, 1993.
7. Ernst Terhardt, Gerhard Stoll and Manfred Seewann, Algorithm for extraction of pitch salience fromcomplex tonal signals, J. Acoust. Soc. Am, 1982.
8. Aaron Hastings and Patricia Davies, Purdue University, An examination of Aures‘s model of tonality,
Proceedings of Internoise2002, 2002.
9. Union of Japanese Scientists and Engineers, Research Committee of Sensory Evaluation, Sen-sory
Evaluation Handbook, JUSE Press, 1973.
10. Seiichiro Namba and Sonoko Kuwano, Psychological measuring method for sound evaluation, Corona
publishing, 1998.

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