The detune effect is actually a version of the pitch shifter. The effect’s result is to increase or decrease the output and combines the pitch shift with the input to vary a few Hz, resulting in an “out of tune effect”. Small pitch scaling values produce a
“chorus like” effect and imitates two instruments slightly out of tune.
References
[1] Gardner, W. G., 1998, “Reverberation Algorithms,” in Applications of DSP to Audio and Acoustics, ed. M. Kahrs, K. Brandenburg, Kluwer Academic Publishers, pp.85-131.
[2] Frenette, J., 2000, “Reducing Artificial Reverberation Requirements Using Time-Variant Feedback Delay Networks”, submitted to the faculty of the university of Miami in partial fulfillment of the requirements for the degree of Master of Science in Music Engineering Technology.
[3] Savioja, L., 1999, “Modeling Techniques for Virtual Acoustics”, Doctorate Thesis, Espoo, Finland,.
[4] Gardner, W. G., 1992, “The Virtual Acoustic Room,” Master’s thesis, MIT Media Lab.
[5] Lee, W. C., Yang, C. H., and Chung-Han Yang, Liu, C. M., and Guo, J. I., 2003,
“Perceptual Convolution for Reverberation,” Audio Eng. Soc. 115th Convention.
[6] Oppenheim A. V., and Schafer, R. W., “Discrete-Time Signal Processing,”
Prentice-Hall, New Jersey.
[7] Gerzon, M. A., 1976, “Unitary (energy preserving) multichannel networks with feedback,” Electronic Letters, 12, No.11, pp. 278-279.
[8] Stautner, J., and Puckette, M., 1982, “Designing Multi-Channel Reverberators,”
Computer Music Journal, 6, No. 1, pp. 52-65.
[9] Dahl, L., and Jot, J. M., “A Reverberator Based On Absorbent All-Pass Filters”, Creative Advanced Technology Center, Scotts Valley, CA, USA.
[10] Rocchesso, D., and Smith, J. O., 1997, “Circulant and Elliptic Feedback Delay Networks for Artificial Reverberation,” IEEE Transactions on speech and audio processing, 5, No. 1.
[11] Tomarakos, J., and Ledger, D., “Using The Low-Cost, High Performance ADSP-21065L Digital Signal Processor For Digital Audio Applications,” Analog Devices DSP Applications.
[12] Lehnert, H., and Blauert, J., 1992, “Principles of Binaural Room Simulation,”
Applied Acoustics 36, pp. 259-291.
[13] 姚賢偉, 1998, “聲場虛擬實境的模擬,” 國立清華大學碩士論文.
[14] Beltra n′ , F. A., and Beltra n′ , J. R., 2002, “Implementing Reverberation Algorithms In Matlab,” J. New Music Research. 31, pp. 153-161.
[15] 曾平順, 2003, “Spatial Reproduction of sound fields,” 國立交通大學博士論 文.
[16] Ouis, D., 2003, “Study on the Relationship between Some Room Acoustical Descriptors,” J. Audio Eng. Soc., 51, No. 6.
[17] Painter, T., and Spanias, A., 2000, “Perceptual Coding of Digital Audio”, Proceeding of The IEEE, 88, No. 4.
[18] Lin, C. T., and Lee, G. C. S., Neural Fuzzy Systems, Prentice Hall, New Jersey.
[19] 陳亙志, 2002, “Multi-Band Room Effect Emulator for 5.1 channel sound system,” 國立交通大學碩士論文.
[20] Dattorro, J., 1997, “Effect Design, Part 2: Delay-Line Modulation and Chorus,” J.
Audio Engineering Society, 10, pp. 764-788.
TABLES
Table 1 The optimized delays of comb filter.
Comb 1 2 3 4 5 6 7 8 9 10
Delay 3007 2825 2753 2656 2499 2341 1784 1712 1482 441
Table 2 The optimized delays and gains of nested allpass filter.
Allpass 1 2 3
Delay 430 248 329
Gain 0.77765 0.88 0.59059
Table 3. The relationship between five subjective indices and five room modes.
ROOMSIZE DIFFUSION WARMTH CLARITY REVERBERATION
Living Room S M S L L
Small Club M L M S M
Church L VL L VL VL
Large
Auditorium VL L VL M S
Gymnasium L S M VL M
(a)
(b)
Figure 1. (a) The two parts of an ideal room response. (b) The impulse response of St.
John's Lutheran Church.
Direct Signal
Early Reflections
Late Reverberation
Time
Figure 2. Energy decay relief (EDR) of a large hall.
y(n) g
z−m
x(n)
Figure 3. (a)
Figure 3. (b)
Figure 3. (c)
Figure 3. (d)
Figure 3. Comb filter. (a) Block diagram. (b) Zero-pole plot. (c) Impulse response. (d) Frequency response.
Figure 4. (a)
Figure 4. (b) -g
g z−m
x(n) y(n)
1-g2
Figure 4. (c)
Figure 4. (d)
Figure 4. Allpass filter. (a) Block diagram. (b) Zero-pole plot. (c) Impulse response. (d) Frequency response.
(a)
(b)
Figure 5. Nested allpass filter. (a) Block diagram (b) Impulse response of the three-layer nested allpass filter with g1=0.5, g2 =0.45, g3 =0.41 and delay lengths m1=441, 533, 617.m2 = m3 =
-g2
g2 ( ) N z x(n)
y(n)
-g1
g1
1
z−m z−m2
( ) N z
(a)
(b)
Figure 6. (a) Stautner and Puckette’s four channel FDN. (b) FDN as general specification of a reverberator containing N delays.
1
(a)
(b)
Figure 7. The results of two channel FDN. (a) The impulse response. (b) The frequency response.
Samples
(a)
(b)
Figure 8. (a) Typical impulse response of the multiple delay effect. (b) The direct-form FIR structure of the multi-tap delay.
1
a1
a2
a3
a4
a5
0 D 2D 3D 4D 5D n h(n)
D1
Z
− Z−D2 Z−D3 Z−D4Z
−D5y(n) x(n)
a1 a2 a3 a4 a5
Figure 9. The impulse response of the Bai’s Reverberator.
samples
Figure 10. The impulse response by using image-source method with n=30, room dimension = [10 8 3] and absorption coefficient is 0.8.
Figure 11. A regular pattern of image sources occurs in a rectangular room.
X
Y : source Z
: receiver
Figure 12. Schroeder’s reverberator consisting of parallel comb filters and serial allpass filters.
Figure 13. (a)
Figure 13. (c)
Figure 13. (a) The structure of each comb filter, where the bp is the gain of absorbent lowpass filter and kp is the gain of comb filter. (b) The structure of ten parallel comb filters and three-layer nested allpass filters. (c) The structure of Nested allpass/comb reverberator with early reflection obtained via image-source method.
y[n]
gr
ge
x[n]
a1 a2 aN
a 0
2
z−m z−mN
1
z−m Nested allpass/comb
(a)
(b)
Figure 14. (a) The geometry of a rectangular room. (b) ELEF as calculated at different position in room.
15m 3m 8m
x
z
y
Source (0.5, 0.5, 2)
Figure 15. The flow chart of the optimization procedure for our scheme.
T60 constraint satisfied ? Search for the 10 Comb filter delays
No
Yes Search for the α
Search for the Comb filter gain Search for the 3-layer
Nested allpass gains and delays
START
FINISH
Step 1
Step 2
Step 3
Step 4
Figure 16. Absolute Threshold in quiet of human hearing.
Figure 17. The block diagram of fast perceptual convolution, where “PSP” is the abbreviation of “perceptual sparse processing”.
Segment
FFT
Memory Memory Memory
Buffer Buffer Buffer
∑
IFFT Buffer
∑
PSP PSP PSP
……
x[n] ……
' 0[ ]
H k H k1'[ ] H k n'[ ]
0[ ]
H k H k1[ ] …… H k n[ ]
y[n]
Figure 18. The spectrum of the segmented impulse response recorded from St. John's Lutheran Church.
Figure 19. General model of fuzzy logic controller and decision making system.
y x Fuzzifier
Plant
Inference Engine
Fuzzy rule Base
Defuzzifier
Figure 20. The scheme of fuzzy user interface for artificial reverberator.
Figure 21. Gauss membership functions for the subjective indices.
Large Medium
Small Very Large
Room_size, Diffusion, Warmth, Clarity and Reverb.
(a)
(b)
(c)
Figure 22. Membership functions of the eight output parameters (a) Output parameter Dim. (b) Output parameter Comb_d. (c) Output parameter Comb_g. (d) Output parameter Apd. (e) Output parameter Fc. (f) Output parameters Alpha,Ge, and Gr.
LL VL
ML SL
5 10 15 20 25 30 50 Dim
LD VD
MD SD
1 1.5 2.5 3 4.5 5 10 Comb_g
LG VG
MG SG
400 600 1200 1400 2400 2600 3000 Comb_d
(d)
Figure 23. The first type－Mamdani’s minimum fuzzy implication rule, Rc.
Figure 24. The fuzzy user interface of artificial reverberator with plot of impulse response.
Figure 25. The fuzzy user interface of artificial reverberator with plot of frequency response.
Figure 26. The fuzzy user interface of artificial reverberator with plot of the EDC and T . 60
Figure 27. The general structure of the Delay-Line Modulation.
Modulating Tap Center of Delay-Line Fixed
Center Tap
a2
af
a1
y(n)
x(n)
Z
-NFigure 28. Common Methods of Modulation.
Sine Square Sawtooth
Reverse Sawtooth Random
LFO Triangular
Figure 29. The structure of a Flanger effect.
Sine Generator Modulates Tap Center of Delay Line
a2 af
a1
y(n)
x(n)
Z
-NSINE
Figure 30. The structure of a 3-instruments Chorus effect.
af2
a2
af1
a1
y(n)
x(n)
Z
-N1a3
Z
-N2LFO 1 LFO 2