WO2007040315A1

WO2007040315A1 - Method and apparatus to generate spatial sound

Info

Publication number: WO2007040315A1
Application number: PCT/KR2006/003867
Authority: WO
Inventors: In-Gyu Chun
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2005-10-01
Filing date: 2006-09-28
Publication date: 2007-04-12
Also published as: EP1929838A4; US8340304B2; US20070074621A1; EP1929838A1; EP1929838B1

Abstract

A spatial sound generation method and apparatus by which reflected sounds of an input sound signal are generated and by using the reflected sounds, a spatial sound is generated. The method includes delaying an input signal by a pplying a specified number of a plurality of delay values to the input signal to generate the specified number of a plurality of reflected sound signals, multiplying each of the delayed reflected sounds by a respective predetermined gain value, and generating additional reflected sounds from each of the gain- multiplied reflected sounds through a feedback loop comprises a delay value and a gain value that are specific for its corresponding gain-multiplied reflected sound signal.

Description

METHOD AND APPARATUS TO GENERATE SPATIAL SOUND

Technical Field

[1] The present general inventive concept relates to a spatial sound system, and more particularly, to a spatial sound generation method and apparatus by which reflected sounds of an input sound signal are generated, and by using the reflected sounds, a spatial sound is generated.

Background Art

[2] Generally, a spatial sound generation apparatus creates a virtual sound source at a predetermined position of a virtual room through headphones or speakers disposed at predetermined locations, and generates a direction effect, a distance effect, and a spatial effect, to make it appear as if the sound that a listener listens to comes from the virtual sound source. For example, the spatial sound generation apparatus generates a spatial sound signal by using reflected sounds, so that the listener can experience a spatial effect and spatial effect through 2-channel headphones, earphones, or speakers.

[3] FIG. 1 is an echogram illustrating a conventional method of generating a reflected sound.

[4] Referring to FIG. 1, the echogram includes a direct sound (non-reflected sound), an early reflected sound, and a late reflected sound (reverberation sound).

[5] The early reflected sound usually uses a tapped delay line method with a tapped delay line including a delay filter and multipliers. The tapped delay line method performs a type of finite impulse response (FIR) filtering, and requires tens to hundreds of delay filters, multipliers, and adders in order to generate tens to hundreds of early reflected sounds.

[6] Also, the late reflected sound is artificially generated by using a Schroeder reverberator as illustrated in FIG. 2. The Schroeder reverberator is mentioned in U.S. Patent No. 5,491,754, titled 'Method and System for Artificial Spatialisation of Digital Audio Signals,' and filed on Feb. 19, 2003.

[7] This Schroeder reverberator includes four parallel-connected feedback comb filters and two serially-connected all-pass filters. An input sound signal x(z) is transferred in parallel through the four feedback comb filters, which have different delay values and gain values, and then added up and output. The added outputs of the four feedback comb filters are transferred through the two serially connected all-pass filters having different delay values and gain values to generate reflected sounds. Finally, the signal passing through the two all-pass filters is output as a sound signal y(z) having a spatial effect.

[8] However, since the Schroeder reverberator does not provide positioning of the reflected sounds, the Schroeder reverberator does not consider directivity, and thus cannot produce sounds that are perceived by a listener to be directional, and is limited at least with respect to generating an accurate virtual spatial sound.

[9] Accordingly, the conventional method of generating a spatial sound using reflected sounds requires a very large amount of computation due to a separate use of the tapped delay line and the artificial reverberator, and does not provide positioning of reflection sound sources.

[10] Besides the conventional technology described above, there are methods using a

Head Related Transfer Function (HRTF) in order to generate a more accurate spatial sound. Disclosure of Invention

Technical Problem

[11] However, since these methods using the HRTF require a very large amount of computation, they are not suitable for portable sound devices.

Technical Solution

[12] The present general inventive concept provides a spatial sound generation method and apparatus capable of providing an effective spatial feeling with a small amount of computation by patternizing a reflected sound and providing a spatial feeling by positioning a plurality of reflected sounds.

Advantageous Effects

[13] According to the present general inventive concept as described above, by using reflected sounds generated with performing delaying and gain-adjusting of an input signal, a spatial stereo sound can be generated. Also, since the present general inventive concept effectively implements a stereo sound in a virtual room without using a HRTF, change in timber scarcely occurs and the amount of computation can be greatly reduced.

[14] Accordingly, the present general inventive concept can be easily applied to mobile devices such as headphones and earphones, such that listeners can listen to a sound signal having a spatial stereo effect almost without change in timbre.

Description of Drawings

[15] These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

[16] FIG. 1 is an echogram illustrating a conventional method of generating a reflected sound;

[17] FIG. 2 is a block diagram of a conventional apparatus for generating a spatial sound; [18] FlG. 3 is a conceptual diagram illustrating a time difference between two ears;

[19] FlG. 4 is a conceptual diagram illustrating generation of a reflected sound in a virtual room according to an embodiment of the present general inventive concept;

[20] FlG. 5 is a block diagram of a basic unit block used in an apparatus to generate a spatial sound according to an embodiment of the present general inventive concept;

[21] FlG. 6 illustrates a pattern of a reflected sound produced by the operation of the basic unit of FlG. 5;

[22] FlG. 7 is a block diagram of an apparatus to generate a spatial sound according to an embodiment of the present general inventive concept;

[23] FIGS. 8A-8D are signal pattern diagrams illustrating a method of generating a reflected sound in the apparatus to generate a spatial sound of FlG. 7, according to an embodiment of the present general inventive concept;

[24] FlG. 9 is a block diagram of an apparatus to generate a spatial sound according to another embodiment of the present general inventive concept;

[25] FIGS. 1OA through 1OF are various different examples of a positioning filter part of

FlG. 9, according to various embodiments of the present general inventive concept; and

[26] FlG. 11 is a flowchart of a method of generating a spatial sound according to an embodiment of the present general inventive concept.

Best Mode

[27] The foregoing and/or other aspects and utilities of the present general inventive concept are achieved by providing a method of generating a spatial sound including: delaying an input signal according to a plurality of different delay values to generate a plurality of reflected sounds; multiplying each of the delayed reflected sounds by a different predetermined gain value; and generating additional reflected sounds by applying a feedback loop that reflects different delay values and gain values to respective multiplied reflected sounds.

[28] The delay values different from each other may be determined based on a size of a predetermined virtual room, and the gain values different from each other may be determined based on a degree of sound absorption of the virtual room.

[29] The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an apparatus to generate a spatial sound including: a delay filter unit to delay one channel signal according to a plurality of different delay values to generate a plurality of reflected sounds; a gain adjusting unit to multiply each of the reflected sounds generated in the delay filter unit by a different predetermined gain value; a feedback comb filter unit to generate additional reflected sounds by applying a feedback loop to reflect different delay values and gain values to respective multiplied reflected sounds; a positioning filter unit to separate each of the reflected sounds generated in the feedback comb filter unit into a first channel signal and a second channel signal, by applying a time difference of times taken to arrive at two ears (or two other sound receiving objects) and a sound pressure difference; and a mixer unit to add all the first channels of each reflected sounds, and to add all the second channels of each reflected sound.

[30] The positioning filter unit may include: an ITD filter to reflect the time difference between the two ears; and an ILD filter to reflect the level difference between the two ears, and the positioning filter unit may output one channel signal without change and output the other channel signal through the ITD filter and the ILD filter.

Mode for Invention

[31] Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.

[32] The present general inventive concept generates a 2-channel stereo sound signal reflecting a stereo effect and a spatial effect from one channel input signal in each channel and uses 2-channel headphones, earphones, or speakers so that a listener can experience a stereo effect and a spatial effect.

[33] The method of obtaining the stereo and spatial effect provides a stereo surround effect which makes a listener (or other sound receiving object) feel as if surrounded by sound, by arranging a plurality of virtual sound sources around the listener. Also, by avoiding in-head localization, which is easily caused by headphones or earphones, the listener is made to feel as if the sound image is localized outside the head. To achieve this, the present general inventive concept designs a virtual room and generates a plurality of reflected sounds such that the listener can experience a sound image effect as if the listener is in a virtual room.

[34] In relation to generation of a stereo sound, the relative direction of a sound source is perceived by a listener due to differences in sound pressure of signals incident on the listener's ears.

[35] Representative perceptions of the direction of a sound source are perceptions by an interaural time difference (ITD) and an interaural level difference (ILD). The ITD indicates a time difference of signals transferred to two ears of a listener caused by a length difference of the paths from a sound source to the two ears, as illustrated in FlG. 3. One way of expressing the ITD is illustrated below in equation 1 :

[36] ITD = r ( θ + sin θ )/C_o (1)

[37] where C denotes the velocity of sound and is about 344m/s.

[38] The ITD can be effectively perceived in a low frequency band equal to or less than about 700Hz.

[39] Meanwhile, the ILD indicates an amplitude difference or level difference of signals transferred to two ears of a listener. The ILD is caused by diffusion of sound occurring mainly in the head and ears.

[40] Accordingly, by perceiving the ITD and ILD, the positioning of a sound source can be ascertained. That is, the ITD can be implemented by a delay value and the ILD can be implemented by adjusting a gain.

[41] Generally, when a stereo sound signal is listened to with headphones or earphones, the sound image is formed inside the head (or between two ears) in many cases. If the sound image is moved so that the sound image is perceived as if the sound comes from two speakers, then the listener can experience a stereo effect.

[42] Meanwhile, in a headphones reproducing system, if a stereo sound is not accurately reproduced or not provided, the in-head localization phenomenon in which a sound image is formed inside the head of the listener is likely to occur. Accordingly, by adding reflected sounds generated in a virtual room to the reproduced sound of the headphones, the in-head localization phenomenon can be removed and the sound image can be made to be formed at a desired location outside the head.

[43] As illustrated in FlG. 4, a reflected sound can be implemented from a simple structural model of a room. FlG. 4 illustrates a mirror image source of a sound source 403 in a given virtual room. The mirror image sound source 405 is a virtual sound source generated by the reflection of the sound source 403 with a surface of a virtual wall as an axis of symmetry. A reflected sound can be modeled by using the mirror image sound source (i.e., mirror image sound source 405) reflected on the virtual wall surface.

[44] That is, the time it takes the reflected sound to travel from the sound source 403 to the ear of the listener 400 can be replaced by the time it takes to travel a straight line distance from the mirror image sound source 405 to the ear of the listener 400. Also, a strength of the reflected sound can be calculated from a strength of the mirror image sound source 405 depending on a degree of sound absorption of the wall surface. Virtual sound sources as well as the original sound source are generated again as an infinite number of sound sources by the sounds reflected by the wall surface of the virtual room. Among the infinite number of virtual sound sources, a finite number of sound sources are set at an appropriate level. Then, the delay time and strength of each virtual sound source are calculated. Then, the ITD and ILD of each virtual sound source are calculated with respect to the incident angle on the listener. Each parameter to be calculated can vary depending on the shape of a given room, a boundary condition, and the positions of the listener and the sound source. Accordingly, in order to generate effective reflected sounds, a virtual room should be designed appropriately. [45] FlG. 5 is a block diagram of a basic unit block used in an apparatus to generate a spatial stereo sound, according to an embodiment of the present general inventive concept.

[46] Referring to FlG. 5, the unit block performs patternization of reflected sounds reflected by any one wall surface of a virtual room. By using a first delay unit 501 and a first gain adjuster 503, a first reflected sound is generated, and a reflected sound pattern related to the first reflected sound is generated through a feedback comb filter including an adder 505, a second delay unit 507, and a second gain adjuster 509.

[47] The first delay unit 501 and the first gain adjuster 503 generate a first reflected sound signal of an input signal as illustrated in FlG. 6. That is, the input signal is delayed by a delay value of the first delay unit 501, and then the gain of the input signal is adjusted by a gain value of the first gain adjuster 503. At this time, if the delay value of the first delay unit 501 and the gain value of the first gain adjuster 503 are appropriately adjusted, a signal identical to a reflected sound of the input signal can be generated in space.

[48] The feedback comb filter including the adder 505, the second delay unit 507, and the second gain adjuster 509, continuously generates additional reflected sound patterns related to the first reflected sound as illustrated in FlG. 6. That is, the feedback comb filter generates a second reflected sound, a third reflected sound, ..., an n-th reflected sound as illustrated in FlG. 6. The pattern of the reflected sounds has an interval of the delay value set in the second delay unit 507, and is output with its level gradually decreasing according to the gain value set in the second gain adjuster 509. Accordingly, if the delay value of the second delay unit 507 and the gain value of the second gain adjuster 509 are appropriately adjusted, a signal pattern very similar to the reflected sounds in space in the psychoacoustic aspect can be generated.

[49] By adjusting the gain value of the second gain adjuster 509, the magnitude

(strength) of a reflected sound fed back to the adder 505 can be adjusted. This corresponds to changing a mean sound absorption rate. Also, in order to change a spatial effect, only the delay value of the second delay unit 507 needs to be changed. That is, if the delay value of the second delay unit 507 is changed, a density of a reflected sound changes as a sound phenomenon and causes an acoustic change in the spatial effect.

[50] Accordingly, if unit blocks of the structure as illustrated in FlG. 5 are connected in parallel, an apparatus to generate a spatial sound according to an embodiment of the present general inventive concept can be constructed.

[51] FlG. 7 is a block diagram of an apparatus to generate a spatial sound according to an embodiment of the present general inventive concept.

[52] The spatial sound generating apparatus of FlG. 7 patternizes reflected sounds reflected by n wall surfaces of a virtual room, and includes a delay part 701, a gain adjusting part 703, a feedback comb filter part 705, and an addition unit 750. In the spatial sound generating apparatus according to the present embodiment, the unit blocks described above with respect to FlG. 5 are arranged in parallel, and the outputs of these unit blocks are added by the addition unit 750.

[53] In the spatial sound generating apparatus of FlG. 7, the delay part 701 includes 1 lth through nl-th delay units 7011 through 70 In, which delay an input signal (IN) by delay times tl 1, t21, ..., tnl, respectively, and output the delayed signals. The gain adjusting part includes 1 lth through nl-th gain adjusters 7031 through 703n, which multiply the outputs of the 1 lth through nl-th delay units 7011 through 70 In, by gain values gll, gl2, ..., gnl, respectively, and output the multiplied signals.

[54] The delay values of the 1 lth through nl-th delay units 7011 through 70 In can be set as delay times taken to travel from n mirror image sound sources, respectively, generated by a virtual sound source positioned in a virtual room, to a listener, and these values depend on the size of the virtual room.

[55] The gain values gll, gl2, ..., gnl, are in proportion to relative sound pressure amounts of the n mirror image sound sources, respectively, generated by the virtual sound source, and these gain values are determined according to the boundary conditions of the virtual room.

[56] The reflected sounds output in parallel from the gain adjusting part 703 are transferred to the feedback comb filter part 705. The feedback comb filter part 705 continuously generates a plurality of reflected sounds obtained by performing delaying and gain-adjusting of each of the reflected sounds input from the gain adjusting part 703, through a feedback loop. That is, from each of the reflected sounds output from the gain adjusting part 703, the feedback comb filter part 705 continuously generates additional reflected sound patterns. If it is assumed that the delay values of the feedback comb filter part 705 are 112, t22, ..., tnl, and the gain values are g 12, g22, ..., gn2, each of these values can be set based on the reflection pattern in a virtual room. In this case, the absolute value of each of the gain values gl 1, gl2, ..., gnl becomes less than 1.

[57] The addition unit 750 generates one output signal by adding each reflected sound output from the feedback comb filter part 705.

[58] FIGS. 8A-8D are signal pattern diagrams illustrating a method of generating a reflected sound in the apparatus to generate a spatial sound of FlG. 7, according to an embodiment of the present general inventive concept.

[59] FlG. 8A illustrates the first reflected sound generated through the 1 lth delay unit

7011 and the 1 lth gain adjuster 7031, and the reflected sound patterns continuously generated through the first feedback comb filter including an adder 7051, a gain adjuster 7091, and a delay unit 7071.

[60] FlG. 8B illustrates the reflected sound generated through the 21st delay unit 7012 and the 21st gain adjuster 7032, and the reflected sound patterns continuously generated through the second feedback comb filter including an adder 7052, a gain adjuster 7092, and a delay unit 7072.

[61] FlG. 8C illustrates the reflected sound generated through the nlth delay unit 70 In and the nlth gain adjuster 703n, and the reflected sound patterns continuously generated through the n-th feedback comb filter including an adder 705n, a gain adjuster 709n, and a delay unit 707n.

[62] FlG. 8D illustrates reflected sounds finally output by adding the reflected sounds of

FIGS. 8A through 8C, which are generated by the respective basic unit blocks.

[63] FlG. 9 is a block diagram of an apparatus to generate a spatial stereo sound according to another embodiment of the present general inventive concept.

[64] The spatial stereo sound generating apparatus of FlG. 9 is different from the embodiment illustrated in FlG. 7 in that the embodiment of FlG. 9 further includes a positioning filter part 911 and a mixer part 950 instead of the addition part 750.

[65] The functions and structures of a delay part 901, a gain adjusting part 903, and a feedback comb filter part 905 are the same as the corresponding parts described above with reference to FlG. 7. However, in the present embodiment, the positioning filter part 911 and the mixer part 950 are further included so that the signal output from the feedback comb filter part 905 is divided into left and right channels and a sound signal with an enhanced stereo effect is generated. Here, the positioning filter part 911 positions a reflected sound by applying characteristics such as the ITD, the ILD, and different ILDs with respect to frequency bands. In FlG. 9, the positioning filter part 911 includes delay filters and gain adjusters, but can be implemented as a variety of combinations by applying an ITD, an ILD, and different ILDs with respect to frequency bands.

[66] Referring to FlG. 9, the feedback comb filter part 905 generates a plurality of reflected sounds which are transferred to the positioning filter part 911 to move a sound image. Each reflected sound input to the positioning filter part 911 to move a sound image is separated into left and right channels, and a reflected sound belonging to one of the left and right channels is transferred to a delay filter and gain adjuster or an ILD filter.

[67] For example, if it is assumed that the sound image of a reflected sound output through a first feedback comb filter including an adder 9051, a delay unit 9071, and a gain adjuster 9091 of the feedback comb filter part 905 is on the left hand side, this reflected sound belongs to the left channel signal and the reflected sound output through a 13th delay unit 9111 and gain adjuster 9131 or an ILD filter belongs to the right channel signal.

[68] It is assumed that the delay values of the 13th through n3-th delay units 9111 through 91 In of the positioning filter part 911 are tl3, t23, ..., tn3, and the gain values of the 13th through n3-th gain adjusters 9131 through 913n are gl3, g23, ..., gn3. The delay values tl3, t23, ..., tn3, and the gain values gl3, g23, ..., gn3 are selected to appropriately set the time and sound pressure differences of respective reflected sounds arriving at a listener's ears, and are dependent on the incident angles of the sounds. Accordingly, if the reflected sounds have different incident angles, respectively, a sound effect with a spatial effect can be generated.

[69] The reflected sounds of the left and right channels output from the positioning filter part 911 are transferred to the mixer part 950.

[70] The mixer part 950 adds together all of the left channel signals and all of the right channel signals of each reflected sound output from the positioning filter part 911.

[71] That is, a first adder 951 adds together all of the left channel signals of each reflected sound separated in the positioning filter part 911 and outputs the result as a left channel signal (Lo), and a second adder 951 adds together all of the right channel signals of each reflected sound separated in the positioning filter part 911 and outputs the result as a right channel signal (Ro).

[72] Finally, the left channel signal (Lo) and the right channel signal (Ro) output from the mixer part 950 are reproduced through headphones and the like so that the listener can listen to the stereo sound.

[73] FIGS. 1OA through 1OF are various different embodiments of the positioning filter part 911 of FIG. 9.

[74] Referring to FIG. 1OA, the positioning filter part 911 can include a delay filter (DL) and a low pass filter (LPF) to realize an ITD and ILD, and a signal belonging to any one of left and right channels goes through the DL and the LPF.

[75] Referring to FIG. 1OB, the positioning filter part 911 can include a DL and an ILD filter to realize an ITD and ILD, and a signal belonging to any one of left and right channels goes through the DL and the ILD filter.

[76] Referring to FIG. 1OC, the positioning filter part 911 can include first and second

DLs (DLl, DL2) and first and second gain adjusters (gl, g2) torealize an ITD and ILD, and left and right channel signals go through the first DL (DLl) and the first gain adjuster (gl) and the second DL (DL2) and the second gain adjuster (g2), respectively.

[77] Referring to FIG. 1OD, the positioning filter part 911 can include first and second

DLs (DLl, DL2) and first and second LPFs (LPFl, LPF2) to realize an ITD and ILD, and left and right channel signals go through the first DL (DLl) and the first LPF (LPFl) and the second DL (DL2) and the second LPF (LPF2), respectively.

[78] Referring to FIG. 1OE, the positioning filter part 911 can include a first DL (DLl) and a first HRTF filter (HRTFl) and a second DL (DL2) and a second HRTF filter (HRTF2) for both channels, and the left and right channel signals go through the first DL (DLl) and the first HRTF filter (HRFTl) and the second DL (DL2) and the second HRTF filter (HRTF2), respectively.

[79] Referring to FIG. 1OF, the positioning filter part 911 can include first and second

HRTF filters (HRTFl, HRTF2) for both channels, and performs convolution operations of the left and right channels with the first and second HRTF filters (HRTFl, HRTF2), respectively.

[80] FIG. 11 is a flowchart of a method of generating a spatial stereo sound according to an embodiment of the present general inventive concept.

[81] First, n reflected sounds are generated through delay filters connected in parallel from an input signal in operation S 1210.

[82] The n reflected sounds can be generated by adjusting the delay and gain of the input signal using different delay values determined with respect to a size of a virtual room and different gain values determined with respect to boundary conditions of the virtual room.

[83] From each of the generated n reflected sounds reflected sounds are continuously generated through a feedback loop in operation S 1220.

[84] Then, positioning of a sound image by applying a time difference of sounds incident on the left and right ears of a virtual listener and a sound pressure difference to each of the generated reflected sounds is performed in operation S 1230.

[85] Accordingly, the reflected sounds from the input signal are generated to provide a spatial effect and by positioning a plurality of virtual reflected sounds, a stereo effect can be generated.

Industrial Applicability

[86] The present general inventive concept can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium can be any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Claims

[ 1 ] L A method of generating a spatial sound comprising : receiving an input sound signal; applying a specified number of a plurality of delay values to the input signal to generate the specified number of a plurality of reflected sound signals; multiplying each of the reflected sound signals by a respective predetermined gain value to adjust the volume of each reflected sound signal; and applying a respective feedback loop to each of the gain-multiplied reflected sound signals, wherein each of the respective feedback loops comprises a delay value and a gain value that are specific for its corresponding gain-multiplied reflected sound signal.

2. The method of claim 1, wherein the delay value s different from each other are determined based on a size of a predetermined virtual room.

3. The method of claim 1, wherein the gain value s different from each other are determined based on a degree of sound absorption of a predetermined virtual room.

4. The method of claim 1, wherein the additional reflected sounds through the feedback loop are generated according to a delay value and a gain value determined based on a pattern of each of the gain- multiplied reflected sounds.

5 . A method of generating a spatial sound comprising: receiving an input sound signal; applying a specified number of a plurality of delay values to the input signal to generate the specified number of a plurality of reflected sound signals; multiplying each of the reflected sound signals by a respective predetermined gain value to adjust the volume of each reflected sound signal; applying a respective feedback loop to each of the gain-multiplied reflected sound signals, wherein each of the respective feedback loops comprises a delay value and a gain value that are specific for its corresponding gain-multiplied reflected sound signal. separating each of the reflected sounds generated from the respective feedback loops into a first channel reflected sound and a second channel reflected sound, by applying a time difference and the sound pressure difference between a two ears to each of the reflected sound s ; and adding all the first channels of each reflected sound divided into the first and second channels, and adding all the second channels of each reflected sound divided into the first and second channels.

6. The method of claim 5, wherein the delay value s different from each other are determined based on the size of a predetermined virtual room.

7. The method of claim 5, wherein the gain value s different from each other are determined based on a degree of sound absorption of a virtual room.

8. The method of claim 5, wherein the separating of the generated reflected sound is positioning the reflected sound by applying an interaural time difference (ITD) and an interaural level difference (ILD).

9. The method of claim 5, wherein the separating of the generated reflected sound is positioning the reflected sound by applying an ITD and an ILD varying with respect to frequency.

10. The method of claim 5, wherein the separating of the generated reflected sound is assigning different delay values to any one of the left and right channels with respect to a different incident angle of each sound.

11. The method of claim 5, wherein the separating of the generated reflected sound is assigning different gain values to any one of left and right channels with respect to a different incident angle of each sound.

12. A method of generating a spatial sound comprising: generating a first reflected sound which is delayed and gain-adjusted according to a predetermined delay value and gain value, from an input signal; and continuously generating reflected sound patterns related to the generated first reflected sound through a feedback loop having a delay value and a gain value.

13. The method of claim 12, wherein the gain value is calculated from a degree of sound absorption of a virtual room.

14. The method of claim 12, wherein the delay value is calculated from a size of a virtual room.

15. An apparatus to generate a spatial sound comprising: a delay filter unit applying a specified number of a plurality of delay values to the input signal to generate the specified number of a plurality of reflected sound signals; a gain adjusting unit to multiply each of the reflected sounds generated in the delay filter unit by a respective predetermined gain value; a feedback comb filter unit to generate additional reflected sounds by applying a respective feedback loop to each of the gain-multiplied reflected sound signals, wherein each of the respective feedback loops comprises a delay value and a gain value that are specific for its corresponding gain-multiplied reflected sound signal; a positioning filter unit to separate each of the reflected sounds generated in the feedback comb filter unit into a first channel signal and a second channel signal, by applying a time difference and a sound pressure difference between the two ears to each of the reflected sound s ; and a mixer unit to add all the first channels of each reflected sounds, and to add all the second channels of each reflected sounds .

16. The apparatus of claim 15, wherein the positioning filter unit comprises: an ITD filter to reflect the time difference between the two ears; and an ILD filter to reflect the sound pressure level difference between the two ears varying with respect to frequency , and the positioning filter unit outputs one channel signal without change and outputs the other channel signal through the ITD filter and the ILD filter.

17. The apparatus of claim 15, wherein the positioning filter unit comprises: a delay filter and a Head Related Transfer Function (HRTF) filter to varying with respect to frequency, and the positioning filter unit outputs the left channel signal through the delay filter and the HRTF filter corresponding to the left ear and the right channel signal through the delay filter and the HRTF filter corresponding to the right ear.

18. The apparatus of claim 15, wherein the positioning filter unit comprises: a delay unit to reflect an ITD ; and a gain adjuster to reflect an ILD , and the positioning filter unit outputs one channel signal without change and outputs the other channel signal through the delay unit and the gain adjuster.

19. The apparatus of claim 15, wherein the positioning filter unit outputs the left channel signal through the HRTF filter corresponding to the left ear and the right channel signal through the delay filter and the HRTF filter corresponding to the r ight ear.

20. An apparatus to generate a spatial sound comprising: a delay filter unit applying a specified number of a plurality of delay values to the input signal to generate the specified number of a plurality of reflected sound signals; a gain adjusting unit to multiply each of the reflected sounds generated in the delay filter unit by a respective predetermined gain value; and a feedback comb filter unit to generate additional reflected sounds by applying a respective feedback loop to each of the gain-multiplied reflected sound signals, wherein each of the respective feedback loops comprises a delay value and a gain value that are specific for its corresponding gain-multiplied reflected sound signal .

21. The apparatus of claim 19, further comprising: an addition unit to add together the additional reflected sounds generated by the feedback comb filter unit and output the added result.

22. A computer readable recording medium having embodied thereon a computer program to execute a method of generating a stereo sound, wherein the method comprises: delaying an input signal by a pplying a specified number of a plurality of delay values to the input signal to generate the specified number of a plurality of reflected sound signals; multiplying each of the delayed reflected sounds by a respective predetermined gain value; and generating additional reflected sounds by applying a respective feedback loop to each of the gain-multiplied reflected sound signals, wherein each of the respective feedback loops comprises a delay value and a gain value that are specific for its corresponding gain-multiplied reflected sound signal.