GB2032673A - Improvements in or relating to sound simulation system - Google Patents

Abstract

In order to generate sounds simulating those sensed in the central operating room of a thermal power plant in operation of a simulated plant, the actual background noise is preliminarily recorded on a magnetic record tape (4) with a constant amplitude. The constant amplitude of the reproduced background noise signal is controlled by an amplitude control device (5) in response to each of digital control signals calculated by a digital computer (2) and applied to the device on a real time basis. The background noise signal controlled in amplitude is converted in a sound simulator (6) to sounds simulating those resulting from the opening of a similater boiler's safety valve, the asynchronous connection of a simulated generator to a simulated electric system etc. upon their occurrence. <IMAGE>

Description

SPECIFICATION Improvements in or relating to sound simulation system This invention relates to improvements in a sound simulation system for use in training operators for operating various plants and more particularly thermal power plants.

In order to operate various plants, it is generally required preliminarily to train operators.

Upon training operators for operating, for example, thermal power plants, a simulated thermal power plant is used to train them for how they will deal with statuses which might actually occur in thermal power plants. The simulated thermal power plant inform training operators or trainees of statuses thereof by means of simulated indicators, alarms etc. disposed therein in the same manner as the actual thermal power plant put in operation. Under these circumstances, if the trainees listen to the types of sound which would be sensed in the central operating room of the actual thermal power plant then the trainees not only look as vivid as if they were present therein but also they can immediately hear the types of sound caused from their operation of the simulated power plant. This gives the trainees the desirable results.

In order to generate sounds simulating what would be sensed in the central operating room of the actual thermal power plant, conventional sound simulation systems have comprised a plurality of magnetic record tapes having recorded thereon the types of sound actually sensed in the central operating room of the actual thermal power plant, sound reproducing devices one for each record tape for reproducing the types of sound from the associated record tapes, and a digital computer for selecting the magnetic record tapes. Therefore only the types of sound recorded on the respective tapes could be reproduced as simulated sounds. In order to increase the types of simulated sound, it has been required to increase the number of the magnetic record tapes and sound reproducing devices accordingly. This has resulted in a large-scaled structure.In addition, it has been necessary to provide a mechanism of rewinding each of the magnetic record tapes after the tape has been completed to reproduce an associated sound.

The present invention provides a sound simulation system for generating different types of sound in continuous or at least overlapped relationship, comprising a sound reproducing device for reproducing a sound recorded on a record medium, the sound having a plurality of frequency components and a predetermined constant amplitude, an electric computer means including a plurality of programs to produce selectively amplitude control signals prescribed to the types of sound respectively, a amplitude control device responsive to each of the amplitude control signals applied thereto to control the predetermined constant amplitude of a signal reproduced by the sound reproducing means, and sound similator for converting an amplitude controlled signal from the amplitude control means into a sound.

The sound recorded on the record medium may preferably comprise the actual background noise to be simulated.

The sound control device may advantageously includes a pair of inputs, a plurality of resistors serially interconnected across the inputs, and a closable switch connected across each of the resistors.

The present invention will more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which: Figure 1 is a block diagram of a conventional sound simulation system for a thermal power plant; Figures 2A, 2B and 2Vare graphs typically illustrating waveforms of sounds to be simulated generated in thermal power plants; Figure 3 is a graph illustrating a sound volume of typical overlapped simulated sound plotted against time and useful in explaining the operation of the arrangement shown in Fig. 1; Figure 4 is a block diagram of a sound simulation system for thermal power plants according to the present invention; Figure 5 is a circuit diagram of the amplitude control device shown in Fig. 4;; Figures 6A, 6B and 6Vare graphs illustrating waveforms of sounds calculated in accordance with function generation programs by the digital cornputer shown in Fig. 4 so as to simulate the sounds illustrated in Figs. 2A, 2B and 2V respectively; Figure 7 is a flow chart illustrating a general program for generating a function; Figure 8 is a graph illustrating a waveform of an overlapped sound calculated by the digital computer shown in Fig. 4 so as to simulate the overlapped sound illustrated in Fig. 3 and useful in explaining the operation of the arrangement shown in Figs. 4 and 5; and Figure 9 is a flow chart useful in explaining the operation of the arrangement shown in Figs.

4 and 5.

In a conventional sound simulation system for a thermal power plant shown in Fig. 1 a sound reproducing device generally designated by the reference numeral 1 includes a plurality of sound reproducing units 1 a, 1 b and 1 vhaving respective magnetic record tapes. The magnetic tape of the unit 1 a has recorded thereon background noise sensed in the central operating room of the actual thermal power plant. An audio signal reproduced from the background noise recorded on the magnetic record tape of the unit 1 a resembles white noise formed of various sounds generated in the actual thermal power plant and is of a constant amplitude as shown in Fig. 2A wherein its sound volume or amplitude is plotted in ordinate against time in abscissa.

The magnetic tape of the unit 1 b had recorded thereon sound due to steam ejected from a safety valve for a boiler involved upon opening the safety valve manually or automatically. As shown in Fig. 2B wherein a sound volume or an amplitude of such a sound is plotted in ordinate against time in abscissa, the sound rises to its peak amplitude upon opening the safety valve and then decreases to and held at a constant amplitude. The magnetic tape of the unit 1 v has recorded thereon a sound generated upon closing a generator involved in asynchronous state with respect to an associated electric system. That sound is shown in Fig. 2C wherein its sound volume or amplitude is also plotted in ordinate against time in abscissa.From Fig. 2V it is seen that the sound rises to its maximum amplitude upon the closure of the generator and then gradually decays as the generator approaches the synchronization with the system until the sound disappears upon the generator reaching the synchronized state.

As shown in Fig. 1, an electric computer, in this case, a digital computer 2 is connected to the sound reproducing device 1 to select the sound reproducing units 1 a, 1 b and 1 vin response to an external command applied thereto from a simulated thermal power plant 3 operated by a trainee and in accordance with the operating status thereof.

The simulated sound signal reproduced by the sound reproducing'device 1 is supplied to a sound output device 4 where it is amplified to a predetermined sound volume. Then the amplified sound signal is converted to an audio sound by a loudspeaker (not shown) disposed therein. The trainee can properly operate the simulated thermal power plant 3 in response to the audio signal from the loudspeaker (not shown).

The operation of the arrangement shown in Fig. 1 will now be described with reference to Fig.

3 wherein there is shown a waveform illustrating a sound volume plotted in ordinate against time, assuming that in the simulated thermal power plant 3 the trainee has opened a simulated boiler's safety valve at time point t, and closed it at time point t2 after which the trainee closes a simulated generator at time point t3 while the synchronous state is not yet reached. That is, the generator is connected across a simulated electric system in asynchronous state.

It is assumed that, at time point to (see Fig. 3) the simulated power plant 3 has been in the predetermined stabilized state. Under the assumed condition, the digital computer 2 receives a command for delivering the background noise and delivers to the sound reproducing device 1 an actuation signal for starting the background noise reproducing unit 1 a. Thus that reproducing unit 1 a responds to the actuation signal to reproduce the background noise signal preliminarily recorded on its magnetic record tape and the sound output device 4 produces an audio signal representing the background noise.

In general, the background noise signal is always reproduced from the sound reproducing device 1 during the operation of the simulated power plant 3 because it is continuously heard in the central operating room of the actual thermal power plant.

At time point t, the trainee has opened the simulated boiler's saftey valve disposed in the simulated power plant 3 with the result that the computer 2 is called for causing the sound reproducing device 1 to reproduce further a signal for a sound due to steam ejected from the opened safety valve such as shown in Fig. 2B. This sound may be called a "valve sound" hereinafter. Thus the computer 2 selects the sound reproducer unit 1 6 two apply an actuation signal thereto. This results in the sound reproducing unit 1 b reproducing a signal for the valve sound preliminarily recorded on its magnetic record tape.

Under these circumstances, the signal for background noise and that for the valve sound reproduced from the respective sound reproducing units 1 a and 1 b are mixed with each other and enter the sound output device 4. The sound output device 4 produces an audio sound having a sound volume or an amplitude L as shown by that portion of the waveform located between time points t1 and t2 in Fig. 3. It is noted that the mixed sound continues to be applied to the sound output device 4 until the safety valve is closed.

At time point t2 the trainee closes the safety valve whereupon the computer 2 receives a command from the simulated power plant 3 to stop the reproduction of the valve sound signal and simultaneously rewind the magnetic tape of the unit 1 b. Thus the sound reproducing unit 1 b is returned back to its initial state to be ready for the next succeeding operation. However, it is to be noted that the sound reproducing unit 1 a continues to deliver the background noise signal to the sound output device 4 after the sound reproducing unit 1 b has been stopped to be operated.

Then time point t3 is reached whereupon the trainee closes a simulated generator disposed in the simulated power plant 3. That is, the generator is connected to a simulated electric system.

At that time, the synchronous state is not yet reached. Therefore the computer 2 responds to a command signal from the simulated power plant 3 to actuate the sound reproducing unit 1 v with the result that the sound output device 4 produces a sound due to the closure of the generator in the asynchronous state mixed with the background noise sound. As shown in Fig.

3, the sound due to the closure of the generator in the asynchronous state (which may be called an "asynchronous generator sound" hereinafter) has a sound volume or an amplitude first increased and then decreased to be less than that of the background noise sound as the synchronous state is approached. Accordingly, at the end of a predetermined time interval, the sound reproducing unit 1 vis stopped and rewinds its magnetic tape. Thus the sound reproducing unit 1 vis returned back to its initial state to be ready for the next succeeding operation.

While the arrangement of Fig. 1 has been described in conjunction with the simplest case using three types of sound only for purposes of illustration it is understood that the sound reproducing device 1 may reproduce the types of sound simulating all the types of sound which may be generated in the normal and abnormal modes of operation of the actual thermal power plant and recorded on respective magnetic tapes. The digital computer 2 responds to a command signal from the simulated power plant 3 to deliver an actuation signal to the sound reproducing device 1. Then the sound reproducing device responds to the actuation signal to reproduce a simulated sound signal recorded on the magnetic tape as determined by the command signal and the reproduced sound signal is applied to the sound output device 4 to be converted to a sound as required.

From the foregoing it is seen that the arrangement of Fig. 1 can reproduce only the types of simulated sound recorded on the respective magnetic tapes. Therefore, in order to increase the types of simulated sound, it has been required to increase the number of the magnetic record tapes and the associated sound reproducing units accordingly resulting in a large-scaled structure. In addition, it has been necessary to provide a mechanism of rewinding each of the magnetic tapes after the generation and stoppage of the associated type of simulated sound.

The present invention contemplates to provide a sound simulation system for generating a multitude of the types of simulated sound with a single set of a magnetic record tape and a sound reproducer without the necessity of rewinding the magnetic tape.

It is very desirable to accustom trainees to various types of sound generated in different modes of operation of the actual thermal power plant and sensed in the central operating room thereof. For example, a valve sound or an asynchronous generator sound signal has an amplitude or sound volume expressed by a function of time as shown in Fig. 2B or 2V and a predetermined frequency component or components. In order to simulate that sound more faithfully, it is desirable to simulate such a sound by means of its frequency and amplitude components. On the other hand, the background noise resembles white noise and includes all audio frequencies. However, when having heard a sound composed of the background noise and the types of sound as shown in Figs. 2B and 2V, the listeners can sufficiently identify the types of sound.It has been found that the satisfactory training effect is exhibited by accustoming trainees to such types of sound.

Fig. 4 shows a sound simulation system according to the present invention. The arrangement illustrated comprises a sound reproducing device 1 includes an endless type magnetic record tape (not shown) having recorded thereon background noise sensed in the central operating room of the actual thermal power plant. The background noise is recorded at a predetermined constant amplitude on the magnetic record tape and includes all audio frequencies resembling white noise as above described. Therefore, the sound reproducing device 1 is adapted to reproduce the recorded background noise into a background noise signal having a predetermined constant amplitude.

The sound reproducing device 1 is connected to an amplitude control device 5 subsequently connected to a sound simulator 6 and also to an electric computer 2 that is connected to a simulated power plant 3 so as to receive command signals from the latter and also to supply data to the latter. In the example illustrated, the computer 3 is of the digital type.

The digital computer 2 includes a plurality of programs each of which generates one digital amplitude control signal applied to the amplitude control device 5 to render the constant amplitude of the black noise from the sound reproducing device 1 substantially equal to an amplitude of a sound to be simulated to the particular sound. The amplitude control device 5 is responsive to the digital amplitude control signal from the computer 2 to control the constant amplitude of the reproduced background noise from the sound reproducing device 1 to be substantially equal to the amplitude of the particular simulated sound.The amplitude controlled signal from the amplitude control device 5 is supplied to the sound simulator 6 where a power thereof is amplified by a predetermined amplification factor and then the amplified signal is converted to a simulated sound by a loud speaker (not shown) included in the sound simulator 6, as in the prior art practice. That is, the loud speaker generates the simulated sound.

The amplitude control device 5 is preferably of a circuit configuration as shown in Fig. 6. The arrangement illustrated comprises a pair of input terminals 5-1, a series combination of resistors 5-2 including an output resistor B0 and a plurality of voltage dividing resistors, in this case, eight resistors, R1, R2,. ., R8 and connected across the input terminals 5-1 in the named order, and a pair of output terminals 5-3 connected across the output resistor R0. The output resistor B0 is connected at one end to ground through one of the input terminals 5-1 and also through one of the output terminals 5-3 while each of the voltage dividing resistor R1 to R8 inclusive connected across a different one of switches S, to S8 inclusive serially interconnected.

For example, the resistor R3 is connected across the switch SW3. The voltage dividing resistor Rn where n is an integer between 1 and 8 inclusive has a magnitude of resistance Rn = 2n-'Ro where B0 designates a magnitude of resistance of the output resistor R0. This expression for the magnitude of resistance holds for any desired integer n. All the switches form a switch group designated by the reference numeral 5-4.

Those switches are connected to receive a binary output N from the digital computer 2 so that each switch is put in its ON state in response to a binary ONE of the output N and in its OFF state in response to a binary ZERO of the output N. Each switch in its ON state shortcircuits the mating voltage dividing resistor while it maintains the mating resistor in its open state when it is in its OFF state.

The operation of the arrangement shown in Fig. 5 will now be described on the assumption that a constant voltage Vjn is applied across the input terminals 5-1 and that an output voltage Vout is developed across the output terminals 5-3. When the digital computer 2 first supplies an output N expressed by a binary number 00000001 corresponding to a decimal number ONE (1) to the switch group 5-4, the switch SW, is put in its ON state while the remaining switches SW2 to SW8 inclusive are put in their OFF state to enable the mating resistors R2 to R8 inclusive.

Thus the output voltage Vout is expressed by B0 V0= Vm R2 + R3 + R4 + R5 + R6 + R7 + R8) + R0 B0 = Vin (2R0 + 22Ro + 23Ro + 24Ro + 25Ro + 25Ro + 27R0) + Ro 1 = Vin 255 Also when the digital computer 2 supplies an output expressed by a binary number 00001010 corresponding to a decimal number TEN (10), the output voltage Vout is similarly expressed by B0 Vo = Vin (20R, + 22Ro + 24Ro + 25Ro + 26Ro + 27R0) + B0 1 = --Vin.

246 In general, the amplitude control device 5 is responsive to a digital number N applied thereto from the digital computer 2 to produce an output voltage VOu, expressed by vout Vjn 28 N where N is an integer having a value of from 1 to 255.

From the foregoing it is seen that the constant amplitude of the background noise signal from the sound reproducing device 1 is controlled to an instantaneous amplitude of the required simulated sound as determined by the binary amplitude control signal from the digital computer 2.

While the amplitude control device 5 has been illustrated and described in conjunction with eight voltage dividing resistors, it is to be understood that any desired number of the voltage dividing resistors may be used, and that, if the number of those registors increases that the simulated sound can be have an instantaneous amplitude more precisely controlled.

The types of sound to simulated have been previously described in conjunction with background noise, a valve sound or a sound due to steam ejected through a safety valve for a boiler and an asynchronous generator sound or a sound due to the closure of a generator in asynchronous state and shown as functions of time in Figs. 2A, 2B and 2V. The functions of time shown in Figs. 2A, 2B and 2V can be analysed to provide functions of time approximating them such as shown in Figs. 6A, 6B and 6V. Fig. 6A shows the function of time approximating the function of time for the background noise illustrated in Fig. 2A, that is to say, simulating the background noise.As seen in Fig. 6A, the simulated background noise is expressed by L(t)= a, (where a1 is a constant) has its initial value set to a zero at its initial time of taO Fig. 6B shows a simulated function of time for a valve sound having its initial value set to a zero at the initial time of tbo and expressed by a combination of functions L(t) = b,t + c1 for tbO~t < tb, L(t) = c2 for tb1t < tb3 L(t) = b2t + c3 for that and L(t) = c3 for tb3t where b1, b2, c1, C2, c3 and c4 are constants. The constant c2 is equal to 28 indicating a maximum output from the amplitude control device 5.

Similarly, Fig. 6V shows a simulated function of times for an asynchronous generator sound.

This function has its initial value also set to a zero at its initial time of t'o and is expressed by a combination of the following two functions: L(t) = v1t + c8 for tVo~t < tv1 and L(t) = v2 for that where v,, v2 and v8 are constants. As shown in Fig. 6V, the function rises from its null value to its peak valve equal to 28 immediately after its initial time tvo and then decreases linearly.

The simulated function such as shown in each of Figs. 6B and 6V can be calculated in accordance with a predetermined function generation program stored in the digital computer 2.

Fig. 7 is a general flow chart of a function generation program for generating a simulated function on the real time basis. In order to generate a simulated function on the real time basis by the digital computer 2, the program is started with one of interrupting clock pulses (not shown) produced by the digital computer to have a predetermined pulse repetition period, for example,100 milliseconds in a step 10 labelled "START". At that time, the program determines if a simulated sound is requested to be generated in the step 1 2. When the simulated sound has been determined not to be requested, the program goes to the steps 1 4 where time point t is reset to a null value and then enters the step 1 6 where the function L(t) is reset to its initial value thereby to deliver an amplitude control signal N = O to the amplitude control device 5 in the step 18. Then the program is completed in the step 20 labelled "END".

However, when the simulated sound is requested as determined in the step 12, the program enters the steps 22 where time point t is added with one unit in response to the next succeeding interrupting clock pulse after which the step 24 is entered. In the step 24 the simulated function L(t + 1) is calculated. The result of the calculation is delivered, as digital amplitude control signal to the amplitude control device 5 in the step 1 8 after which the program is completed in the steps 20 and then ready for the next succeeding operation. The process as above described is repeated in response to the succeeding interrupting clock pulses to deliver the digital amplitude control signals to the amplitude control device 5 in the real time basis. This results in the required simulated sound being produce by the sound simulator 6.

Fig. 8 is a graph illustrating typically three types of simulated sound succeessively produced by the arrangement of Fig. 4 when the trainee is operating the simulated thermal power plant 3.

In Fig. 8 the amplitude N of the simulated sound is plotted in ordinate against time tin abscissa. In order to produce the simulated sound having the amplitude shown in Fig. 8 on the real time basis, the digital computer 2 generates the digital amplitude control signal N in accordance with a program stored therein and on the real time basis. The program is excuted in accordance with a flow chart shown in Fig. 9.

More specifically, the program responds to one of the interrupting clock pulses as above described in conjunction with Fig. 7 to be started in the step 30 labelled "START" and goes to the step 32 where it is determined whether or not the simulated plant 3 is in its predetermined operation. When the simulated plant 3 is determined not to be in its predetermined operation, the program enters the step 34 which generates a digital amplitude control signal N having a null value and is completed in the step 36 labelled "END".

In the other hand, it is assumed that the simulated thermal power plant is in its predetermined operation with the simulated safety valve closed and without the simulated generator connected to the simulated electric system. Under the assumed condition, the program responds to one of the interrupting clock pulses to determine in the step 32 that the simulated plant is in its predetermined operation and goes to the step 38. In the step 38 a function program for the background noise is executed to calculate a simulated function thereof L(t) = constant in accordance with the succeeding interrupting clock pulses and deliver a digital amplitude control signal Na having a constant value on the real time basis.The process just described continues to proceed for tot < t, shown in Fig. 8 because the trainee opens the simulated safety valve at time point of tt.

At time point t the program enters the step 46 where the opening of the simulated safety valve is determined. Following this, the program goes to the step 42 where a simulated function L(tÙ) for the valve sound is calculated following a function program therefor as above described in conjunction with the steps 22 and 24 shown in Fig. 7 and a digital amplitude control signal Nb = L(tb) for the valve sound is added to that for the background noise Na. Thus the sum of both signal Na + Nb is delivered from the electronic computer on the real time basis.

As shown in Fig. 8, the simulated safety valve is again closed at time point t3 after which the step 44 calculates the signal Nb having a null value in the same manner as above described in conjunction with the steps 14 and- 1 6 shown in Fig. 7. Accordingly, the digital computer 2 continues to deliver only the digital amplitude control signal Na having a null value on the real time basis.

Then at time point t4 the simulated generator is closed while the synchronous state is not yet reached. The program responds to an interrupting clock pulse occurring at that time to enter the step 46 where it is determined that such closure of the simulated generator has been accomplished. Therefore, the step 48 is entered and calculates a simulated function L(tV) for a generator sound in the similar manner as above described in conjunction with the step 42 resulting in the provision of a digital amplitude control signal Nv therefor. This amplitude control signal Nv is added to the amplitude control signal Na plus that Nb in the step 52 to form a digital amplitude control signal N equal to the sum of Na, Nb and Nv.Thereafter the digital amplitude control signal N on the real time basis is delivered to the amplitude control device 5 in the step 54 until time point t5 is reached. At and after that time point, the simulated generator approaches or reaches the synchronous state resulting in only the background noise remaining. Under these circumstances, the step 50 is enabled to generate the signal Nv having a null value in the same manner as the step 44, and the step 54 delivers the signal Na alone.

The program is completed in the step 56 labelled "END" and ready for the next succeeding operation.

The amplitude control device 5 controls the constant amplitude of background noise signal from the sound reproducing device 1 dependent upon the digital amplitude control signal N from the electronic computer 2 to cause the sound simulator 6 to produce simulated sound having an amplitude equal to that shown in Fig. 8.

In summary, the present invention provides a sound simulation system comprising an electric computer responsive to a demand for generating simulated sound dependent upon the operating status of an associated simulated plant to calculate a digital amplitude control signal in accordance with a program stored therein, to instruct that the simulated sound is equal in amplitude to the actual sound generated in the actual plant, an amplitude control device receiving the digital amplitude control signal to control a constant amplitude of a signal reproduced by a sound reproducing device thereby to form a sound signal equal in amplitude to the simulated sound, and a sound simulator connected to the amplitude control device to convert the sound signal to the simulated sound.

While the present invention has been described in conjunction with a magnetic record tape having recorded thereon a sound the same is equally applicable to any record medium such as magnetic recording discs, optical films etc. having constant amplitude sound recorded thereon.

The constant amplitude sound has been described as background noise sensed in the central operating room of the actual thermal power plant but the present invention is not restricted thereto or thereby. Instead of sound actually generated in plants to be simulated and recorded on record medic other types of sound may be utilized without recording sounds actually generated. Alternatively, one may employ electrically composed sounds.

Also the amplitude control device may include a rotary variable resistor whose resistance is variable by an associated electric motor. Alternatively, it may include an amplifier having a controllable degree of amplification so as to produce an output amplitude as desired.

Further, in order to deliver the digital amplitude control signal to the amplitude control device, it is possible to employ the process executed in general electric computers. For example, the function generation program may be constructed so that the amplitude of simulated sound is approximated by higher order functions rather than linear functions as above described.

In addition, a plurality of the amplitude control devices may be operatively combined with respective sound reproducing devices. Also, the present invention is equally applicable to a variety of simulated apparatus other than simulated thermal power plants and to a variety of training apparatus.

Claims (9)

1. A sound simulation system for generating different types of sound in continuous or at least overlapped relationship, comprising a sound reproducing device (1) for reproducing a sound recorded on a record medium, said sound having a plurality of frequency components and a predetermined constant amplitude, an electric computer (2) including a plurality of program to produce selectively amplitude control signals prescribed to the types of sound respectively, an amplitude control device (5) responsive to each of said amplitude control signals applied thereto to control the predetermined constant amplitude of a signal reproduced by the sound reproducing device (1), and sound simulator (6) for converting an amplitude controlled signal from said amplitude control device (5) into a sound.

2. A sound simulation system according to claim 1 characterized in that said sound reproducing device (1) reproduces said signal in the endless form.

3. A sound simulation system according to claim 1 characterized in that said record medium comprises a selected one of a magnetic record tape, magnetic record disc and an optical film.

4. A sound simulation system according to claim 1 characterized in that said record medium has recorded thereon the actual background noise to be simulated.

5. A sound simulation system according to claim 1 characterized in that said amplitude control device (5) includes a plurality of voltage dividing resistors (R1, R2, R3, R4, R5, R6, R7 and R8) and a plurality of switches (SW,, SW2, SW3, SW4, SW8, SW8, SW7 and SW8) operatively coupled to said plurality of resistors respectively.

6. A sound simulation system according to claim 5 characterized in that said amplitude control device (5) includes two input terminals (5-1), said plurality of voltage dividing resistors being (R, to R8 inclusive) serially interconnected across said two input terminals (5-1) and each of said switches (SW, to SW6 inclusive) is connected across a different one of said resistors.

7. A sound simulation system according to claim 6 characterized that an output resistor (Ro) and n voltage dividing resistors (B1, R2, . . ., Rn) are serially interconnected across said two input terminals (5-1) in the named order and that the voltage dividing resistor R, where iis an integer between 1 and n has a magnitude of resistance Ri = 2i- 'Ro where B0 also designates a magnitude of resistance of the output resistor (R,).

8. A sound simulation system according to claim 1 characterized in that said amplitude control device (5) comprises an amplifier having a controllable degree of amplification so as to produce an output amplitude as desired.

9. A sound simulation system substantially as described herein and with respect to Fig. 4 of the accompanying drawings.

1 0. A sound simulation system substantially as described herein and with respect to Figs. 4 and 5.