fig1 is a configuration view showing a game system 1 as an embodiment of the present invention . the game system 1 is constituted of a game - machine main assembly ; a television monitor 2 ( which is called a “ monitor ”, hereinbelow ) as display means for displaying game screens ; an amplifier circuit 3 and a speaker 4 ( sound - generating means ) for outputting game sounds ; and a recording medium 5 in which image data , sound data , and a game program composed of program data are recorded . the recording medium 5 is , for example , a so - called cassette rom , an optical disk , or a flexible disk that is housed in a plastic package , in which program data for , for example , the aforementioned game program and an operating system are stored . the game - machine main assembly is configured such that a bus 7 composed of an address bus , a data bus , and a control bus are connected to a cpu 6 ; a ram 8 , an interface circuit 9 , an interface circuit 10 , a signal processor 11 , an image processor 12 , an interface circuit 13 , and an interface circuit 14 are individually connected to the bus 7 ; a controller 16 is connected to the interface circuit 10 via an operation - information interface circuit 15 ; a d / a converter 17 is connected to the interface circuit 13 ; and a d / a converter 18 is connected to the interface circuit 14 . in this , the ram 8 , the interface circuit 9 , and the recording medium 5 , as described above , constitute a memory section 19 ; the aforementioned cpu 6 , the signal processor 11 , and the image processor 12 , as described above , constitute a control section 20 that controls the game progress ; the interface circuit 10 , the operation - information interface circuit 15 , and the controller 16 , as described above , constitute an operation - input section 21 ; the monitor 2 , the interface circuit 13 , and the d / a converter 17 constitute an image display section 22 ; and the amplifier circuit 3 , the speaker 4 , the interface circuit 14 , and the d / a converter 18 constitute a sound - output section 23 . the signal processor 11 mainly performs computations in a three - dimensional space , computation for positional transformation from a three - dimensional space to a pseudo - three - dimensional space , computation of light sources , and generation and processing of sound data . the image processor 12 performs writing of image data , that is , writing of texture data , which is to be written in a display area of the ram 8 . the controller 16 has externally - operable operating means including a start button 16 a , an a - button 16 b , a b - button 16 c , a cross key 16 d , a stick - type controller 16 e , a left trigger button 16 f , a right trigger button 16 g , a c1 button 16 h , a c2 button 16 i , a c3 button 16 j , a c4 button 16 k , and a depth trigger button 16 n , and sends signals corresponding to operations effected on the individual buttons to the cpu 6 . the stick - type controller 16 e has substantially the same arrangement as a joystick . that is , it has a stick installed upright therein , which is bendable in a direction of 360 ° around a predetermined support point , including the left - right and back and forth directions . conforming to the bend direction and bend angle of the stick , an x - coordinate value in the left - right direction and a y - coordinate value in the back and forth direction , both coordinates being based on the original upright position , are arranged to be sent to the cpu 6 via the interface circuits 15 and 10 . the controller 16 also has a connector 16 m from which , for example , a card - type memory for temporarily memorizing , for example , the game progress status , is detachable . the game system 1 , as described above , varies in configuration according to its use . for home - use configuration of the game system 1 , the television monitor 2 , the amplifier circuit 3 , and the speaker 4 are spaced from the game - machine main assembly . for commercial - use configuration of the game system 1 , however , all the components shown in fig1 are integrally stored in a single housing . also , when the game system 1 is configured on the basis of a personal computer or a workstation as a nucleus , the television monitor 2 corresponds to a display unit of the computer ; the image processor 12 corresponds to part of the game program data recorded in the recording medium 5 or hardware on an expansion board mounted on an expansion slot of the computer ; and interface circuits 9 , 10 , 13 , and 14 , d / a converters 17 and 18 , and the operation - information interface circuit 15 correspond to the hardware on the expansion board mounted on the expansion slot of the computer . also , the ram 8 corresponds to a main memory or individual areas of an expansion memory of the computer . in this embodiment , a description will be given taking an example case where the game system 1 is configured for home use . hereinbelow , an overall operation of the game system 1 is described below . when a power switch ( not shown ) is turned on , and the game system 1 is powered on , the cpu 6 performs reading of image data and sound data , and the game program from the recording medium 5 in accordance with an operating system stored in the recording medium 5 . all or some of the data read out are transferred to the ram 8 to be stored therein . subsequently , the cpu 6 commands the game to proceed on the basis of the game program data contained in the ram 8 and the type of instructions a game player issues using the controller 16 . in particular , the cpu 6 generates commands as tasks for , for example , creating images and outputting sounds , according to operation signals sent from the controller 16 as and when required by instructions the game player issues using the controller 16 . in response to the above - described commands , the signal processor 11 performs computations such as character - position computation and light - source computation in a three - dimensional space ( the same as in a two - dimensional space , as a matter of course ), and in addition , functions as output control means for performing generation of sound data . on the basis of results of the aforementioned computations , the image processor 12 performs writing of image data that must be drawn in a display area of the ram 8 , and the like . the d / a converter 17 converts the image data written in the ram 8 to an analog signal in every predetermined cycle via the interface circuit 13 and then displays the signal as an image on a tube face of the monitor 2 . on the other hand , the data which has been outputted from the signal processor 11 is fed , via the interface circuit 14 , to the d / a converter 18 in which the data is converted to an analog signal , and the signal is then outputted from the speaker 4 via the amplifier circuit 3 as sounds . hereinbelow , referring to fig2 and 3 , a description will be given of an outline of a video game to be executed by the game program recorded in the recording medium 5 . fig2 and 3 each show a screen of the game . this video game is such that , according to the operations performed by a game player on the controller 16 by a game player , a leading character performs actions such as battles with an opponent character , and obtains items so as to satisfy predetermined conditions to be cleared in a game stage , whereby the game proceeds to the next stage . as shown in fig2 and 3 , a leading character 30 is displayed substantially in the center of the screen of the monitor 2 , and around the leading character 30 , as models representing geometrical shapes and structural elements . fig2 shows a display of rock models 31 , and fig3 shows a display of a shrine - gateway models 32 . also , the lower portion of the monitor 2 displays weapon items the leading character 30 is to carry and a game - status display section 33 for displaying a life gage . also , in this video game , game time that runs at a predetermined rate according to the passing game time is set , and a daytime / nighttime status display section 34 is provided in the game - status display section 33 . in the daytime / nighttime status display section 34 , display contents of the upper semicircular section are rotated clockwise around the center of a circular display section , and colors ranging from light blue to white ( which are displayed by reticulate dots in fig2 and 3 ) indicate daytime , and a star and crescent marks indicate nighttime . in this way , according to the display status in the upper semicircular section , the daytime / nighttime status of the game time is identifiably displayed . for example , the daytime / nighttime status display section 34 in fig2 indicates early morning time , and the daytime / nighttime status display section 34 in fig3 indicates evening time . the running rate of the game time is set independently of the game stage that proceeds according to the type of operation effected on the controller 16 . therefore , even in the same game screen , the daytime / nighttime status differs depending on the rate of operation effected on the controller 16 . fig4 is a schematic view showing function blocks of the cpu 6 and main portions in fig1 . fig5 is a drawing showing sound - level control functions . fig6 is a drawing illustrative of partitioning codes . as described above , the recording medium 5 contains the game program . it also contains data such as a sound - level control function 51 , multiple pieces of background - sound data 52 , and partitioning codes 53 as part of the game program . in this invention , the recording medium 5 is also referred to as function - storing means or background - sound - data storing means . as described below , the sound - level control function 51 is used in computation of data to produce output ratios of sound levels predetermined with the background - sound data 52 when the background - sound data 52 is outputted to the d / a converter 18 , and a first function 51 a and a second function 51 b as shown in fig5 are stored in the recording medium 5 . the first function 51 a is predefined so that the output ratio increases sharply from 0 %, and thereafter , increases gradually up to 100 %. the second function 51 b is predefined so that the output ratio decreases gradually from the output ratio of 100 %, and thereafter sharply decreases from 100 %. in this embodiment , quadratic functions are used as the first and second functions 51 a and 51 b . for the multiple pieces of background - sound data 52 , for example , the background - sound data for the nighttime and the background - sound data of daytime are prepared individually according to game stages and game times . the background - sound data 52 is composed of a plurality of channels , and quasisounds , such as a “ japanese drum ”, a “ bass ”, and a “ synthesizer sound ”, are composed in the individual channels . the partitioning code 53 represents the end position of a phrase of the background sound ( the natural division of a melody flow ) outputted from the speaker 4 , as shown in fig6 . a data number 54 of the other background - sound data is temporarily stored in the ram 8 when background - sound data being outputted to the d / a converter 18 is switched to other background - sound data . the ram 8 is also referred to as standby - data storing means . the cpu 6 controls operations of individual system - configuration elements according to the game program . it has operation - detecting means 60 , game - progress control means 70 , and sound control means 80 . the operation - detecting means 60 detects the type of game - player operation of the controller 16 according to an operation signal sent from the controller 16 . the game - progress control means 70 controls the game progress according to the type of operation of the controller 16 and the game program , and concurrently , has a function for controlling images displayed on the monitor 2 . in addition , as functional blocks , the game - progress control means 70 includes game - time control means 71 , switching instruction means 72 , and start instruction means 73 . the sound control means 80 generates a sound - outputting command for the background sound and effect sounds ; and as functional blocks , it has sound - level control means 81 , data - number control means 82 , code - detecting means 83 , and switching control means 84 . the game - time control means 71 in the game - progress control means 70 runs the game time at a predetermined rate according to the elapsed game time , and also controls the display contents of the daytime / nighttime status display section 34 . the switching instruction means 72 outputs a switching instruction signal which causes switching from the background - sound data being output to the d / a converter 18 at such a moment when the game stage is switched or the daytime / nighttime status is changed either from daytime to nighttime or from nighttime to daytime . the start instruction means 73 outputs a start signal that instructs start of crossfading sound - level control , which is described below , when the game time passes to a predetermined point . the sound - level control means 81 in the sound control means 80 controls the output ratio on the basis of the channels when background - sound data is outputted through the speaker 4 according to the sound level set in the background - sound data 52 . upon the output of the switching instruction signal , the data - number control means 82 stores the data number 54 defining the background - sound data 52 in a predetermined area of the ram 8 . the code - detecting means 83 detects the partitioning code 53 appended to the background - sound data 52 being outputted to the d / a converter 18 . ( 1 ) a function as data - number determining means that determines whether or not the data number 54 defining the background - sound data 52 is stored in the predetermined area of the ram 8 after each detection of the partitioning code 53 . ( 2 ) a function as data switching means that switches from the background - sound data 52 being outputted to the d / a converter 18 to other background - sound data 52 to be defined by the data number 54 when the data number 54 defining the background - sound data 52 is stored in the predetermined area of the ram 8 . hereinbelow , referring to fig5 and 7 , a description will be given of crossfading sound - level control to be performed by the sound - level control means 81 . fig7 shows timing charts indicating output ratios of individual channels for sound levels defined in the background - sound data . fig7 shows a case where the daytime / nighttime status of the game proceeds from nighttime to daytime , and the outputted background - sound data is switched from nighttime background - sound data to daytime background - sound data . in this embodiment , the individual background - sound data is composed of six channels , which are a first channel to a sixth channel . the individual pieces of nighttime background - sound data are composed of quasisounds of , for example , a “ japanese drum ”, a “ bass ”, a “ synthesizer ”, a “ nighttime main melody ”, a “ first drum ”, and a “ second drum ”. the individual pieces of daytime background - sound data are composed of quasisounds of , for example , a “ bamboo flute ”, a “ flute ”, a “ bass ”, a “ daytime main melody ”, a “ first drum ”, and a “ second drum ”. as fig7 shows , as output ratios of the individual channels of the nighttime background - sound data for the defined sound level , those for the first channel to the fourth channel are maintained at 100 % from the beginning , and those for the fifth channel and the sixth channel are maintained at 0 % from the beginning . when a start signal is outputted at a time t 1 , crossfading sound - level control is performed according to the sound - level control function 51 . that is , output ratios of the first channel to the fourth channel are reduced from 100 % according to the second function 51 b ; and output ratios of the fifth channel and the sixth channel are increased from 0 % according to the first function 51 a . when the game time proceeds , a switching instruction signal is outputted at a predetermined time t 2 , and thereafter , a partitioning code is detected at a time t 3 , the nighttime background - sound data is switched synchronously to the daytime background - sound data , and the output ratios of the individual channels in the daytime background - sound data are maintained at 100 %. in the above case , the “ first drum ” of the fifth channel and the “ second drum ” of the sixth channel are continuously used in the fifth channel and the sixth channel of the daytime background - sound data . therefore , the background sound to be outputted through the speaker 4 changes gradually from the time t 1 . this allows the background sound to be suitably switched . also , the background sound is switched in synchronous with detection of the partitioning code appended to each phrase . in this case , since the background sound does not suddenly switch but switches naturally , even when the background - sound data is switched , the boundary cannot be perceived by the ear . thus , switching of the background - sound data can be smoothly performed , thereby allowing switching of the background - sound data to be performed even more suitably . in this embodiment , from the time when the start signal is outputted , output ratios of the first channel to the fourth channel are gradually reduced from 100 %, and output ratios of the fifth channel and the sixth channel are increased sharply from 0 %. according to experiments by the inventor and others , compared to the case where the individual channels are linearly increased or reduced , switching of the background sound to be outputted through the speaker 4 can be determined even more clearly . hereinbelow , referring to the flowchart in fig8 a description will be given of operation steps of a background - sound switching program , which switches the background - sound data . the program determines whether or not a switching instruction signal has been outputted according to progress in the game time , the game , and the like ( step st 10 ). if the switching instruction signal is outputted ( yes in step st 10 ), a data number defining the next background - sound data is stored in the ram 8 ( step st 20 ). if the switching instruction signal is not outputted ( no in step st 10 ), control proceeds to step st 30 . subsequently , the program determines whether or not a partitioning code is detected in the background - sound data currently being outputted ( step st 30 ). if a partitioning code is detected ( yes in step st 30 ), the program determines whether or not a data number is stored in the ram 8 ( step st 40 ). if a data number is stored ( yes in step st 40 ), the background - sound data is switched ( step st 50 ). if a partitioning code is not detected ( no in step st 30 ), or if a data number is not stored in the ram 8 ( no in step st 40 ), control returns to step st 10 . hereinbelow , referring to the flowchart in fig9 a description will be given of operation steps of a background - sound control program for the crossfading sound - level control by the sound control means 80 . this routine is executed as a process - interrupting routine in each predetermined cycle . first , the program determines whether or not a start signal for the crossfading sound - level control is outputted ( step st 110 ). if the start signal is outputted ( yes in step st 110 ), initialization is performed for the crossfading sound - level control , a flag representing that the crossfading sound - level control is in progress is set ( step st 120 ), and control proceeds to step st 130 . if the start signal is not outputted ( no in step st 110 ), the program determines whether or not the crossfading sound - level control is already being processed ( step st 130 ). if the crossfading sound - level control is in process ( yes in step st 130 ), output ratios of the individual channels are computed by using the sound - level control function 51 from a passing time from the time when the start signal is outputted ( step st 140 ). that is , in the example in fig7 output ratios of the first channel to the fourth channel are computed according to the second function 51 b , and output ratios of the fifth channel and the sixth channel are computed according to the second function 51 b . subsequently , sound levels for the individual channels are computed using the computed output ratios . in specific , absolute values representing sound levels that must be outputted through the speaker 4 are computed ( step st 150 ), the computed sound levels for the individual channels are written into predetermined areas of the ram 8 , and then this routine ends . if the crossfading process is not in progress in step st 130 ( no in step st 130 ), default sound levels set in the background - sound data are written for individual channels ( step st 160 ). then , this routine ends . in this way , according to this embodiment , output ratios of sound levels of the first to fourth channels are maintained at 100 %, and output ratios of sound levels of the fifth and sixth channels are maintained at 0 %. in this , when the start signal is outputted , the output ratios of the first to fourth channels are reduced , and concurrently , the crossfading sound - level control is performed to increase the output ratios of the fifth and sixth channels . this allows smooth switching background - sound data to be outputted through the speaker 4 from nighttime background - sound data to daytime background - sound data . in this way , switching of the background - sound data can be performed suitably . also , switching of the background - sound data can be performed so as to be heard even more easily . this can be achieved when the daytime background - sound data after switching is arranged to include quasisound data which has been set in the firth and sixth channels increased by the crossfading process from the pre - switching state to 100 % set . also , the partitioning code 53 representing the end position of the phrase of the background - sound data is provided , and the background - sound data is switched synchronously at the time when the partitioning code 53 is detected . this prevents unnatural changes which may be felt when the background sound is switched during processing of a phrase , and the boundary of switching is perceived by the ear . in this way , background - sound data can be suitably switched . also , since a prefixed sound source such as that implemented for recording media , for example , cd - roms , is not used , the background sound can be generated in the real time depending on the game status . the present invention is not restricted to the above embodiment and may employ modifications described below . ( 1 ) in the above embodiment , as the first and second functions 51 a and 51 c , quadratic functions are used . however , there is no such restriction . as long as the first function 51 a allows the output ratio to increase sharply from 0 % and allows the second function 51 b to decrease gradually from 100 %, the functions may be trigonometric functions , exponential functions , logarithmic functions , or other functions . ( 2 ) in the above embodiment , the background - sound data is switched according to the game time . however , there is no such restriction . the background - sound data may be switched , for example , in each change of the game stage , such as places where the main character battles the opponent character , and stairs in a castle and a building . ( 3 ) in the above embodiment , the output ratio of each channel is either increased or reduced . however , there is no such restriction . the output ratio of the sound level of a predetermined channel may be increased or reduced according to the game status relevant to , for example , the number of opponent characters . for example , in fig1 , when the number of opponent characters increases , the output ratio of the first channel increases , and concurrently , the output ratio of the second channel decreases . also , when the number of opponent characters decreases , the output ratio of the first channel decreases , and concurrently , the output ratio of the second channel increases . in the case of fig1 , for the sound - level control function 51 , a function allowing the output ratio to increase and decrease in the range of 0 % to 100 % is preferably set . in this case , the number of channels of background - sound data is not restricted to the number shown in fig7 and 10 , and the number may be at least one . according to this mode of the invention , even when the number of cpu - usable output ports is restricted , whereby the number of channels of the background - sound data is restricted , variation can be provided in the background sound . this allows effectiveness of the background sound to be improved . ( 4 ) the above embodiment is a video game apparatus which the game player operates . however , there is no such restriction . the apparatus may be an image - creating apparatus that outputs background sounds corresponding to images displayed on the monitor 2 . also , the display means is not restricted to the image display apparatuses , such as a monitor , and other display means of various types , such as mechanical , optical , and acoustic types may be considered to be used . the display means includes , for example , the type for a so - called “ mole - whacking game ”. in this case , variation in popping - up of moles , the popping - up rate , the popping - up count , and the like , is displayed as the event variation . ( 5 ) in the described embodiment , the first channel to the fourth channel are faded out to be silent and are then switched . however , there is no such restriction . the channels may be switched before they are faded out to be silent . in this case , the background - sound data before or after switching is set so that the background sound can be heard naturally . ( 6 ) in the described embodiment , the output ratio of the background - sound data is varied according to the variation in the game time . however , there is no such restriction . the output ratio may be varied according to variation of the image displayed on the monitor 2 , and variation of the operations performed on the controller 16 . also , the output ratio may be varied according to variation of an event such as moles that pop up in the case of the so - called mole - whacking game . ( 7 ) switching of the background - sound data may be varied according to variation of the operation effected on the controller 16 . also , the switching may be varied according to the variation - of an event such as moles popping up as in the mole - whacking game .
a background - sound control apparatus , a background - sound control method , readable recording medium containing a background - sound control program , and a video game apparatus improve effectiveness of background - sound data provided over a predetermined number of channels . when background sounds are produced through a speaker , a sound - level controller controls output ratios for sound levels defined in background - sound data on a channel basis and uses a sound - level control function to perform crossfading sound - level control .