CA1231308A - Waveform to sound pattern converter - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention produces an audible image of a time dependent signal by digitizing the signal to produce a plurality of discrete level signals, and producing a different audible tone signal for each level of the discrete level signals.
A speaker is provided for producing audible sounds and circuitry is provided for driving the speaker to produce an audibly perceptible reference frame indicative of a predetermined time duration and also for driving the speaker with the audible tone signals such that the audible tone signals have the same time orientation with respect to each other as the discrete level signals have in the tire depen-dent signal.

Description

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WAVEFORM TO Sound PATTERN CONVERTER

BACKGROUND OF TIE INVENTION

Field of the Invention This invention relates to systems for converting electrical signals into wound patterns and more particularly to systesns which can convert the visual readout of an instrument such as an oscilloscope into a sound pattern representative of the visual readout.

Discussion of Related Art .

The vast major fly of instrulaents used for measure in and testing apply Asians use visual radix to indicate the quantity being measured Such instruments, such as a oscilloscope are invaluable in certain fields of endeavor. Louvre, these instruments have certain drawbacks. First, it is necessary that a user focus his or her attention on the visual readout in order to be constantly aware of the status of the measured quantity. Therefore, if the user wishes to make adjustments to a system containing the measured parameter, he or she must either make the adjustments without keeping careful track of the effect of the adjustment as indicated on the visual readout, or must constantly watch the readout and make the adjustments only by physically feeling the elements briny adjusted.
Furthermore, these instruments cannot be used by persons handicapped by limited sight If such a person is to use, for example, an oscilloscope, he or she must have someone else provide an aural description of the status of the visual readout.
Consequently it would be useful to have a system which can directly produce an audible representation of a measured parameter in order to replace or augment a measuring instrument such as an oscilloscope. Such an instrument could produce a sound pattern representative of the visual pattern of an ordinary oscilloscope or other measuring and testing instrumentation.
Systems are already known for producing sound pattern representations of curtain quantities.
For example, U.S. Patent No. 3,007,259 to Alma et at shows an optophone which comprises an optical head that can ye passed over printed material. The system produces a unique sound pattern for each letter of the alphabet to enable a sightless person to read the printed material aurally.

I Jo U.S. Patent No. 3,800,0~2 to Fish discloses a system for producing sound patterns representing various objects wherein the raster scan display of an oscilloscope CRT is detected by a photo multiplier tube. The object to be represented is placed between the CRT and photo multiplier tube. The signal from the multiplier tube causes a sound to be generated repro-setting the position of the illuminated portion of the oscilloscope CRT which is not covered by the object.
U.S. Patent No. 3,907,434 to Coxes discloses a binaural sight system it which two cameras are used which generate image signals representative of optical images projected there onto. The cameras are positioned in horizontally spaced relation and are independently connected to right and left earphones.
The cameras are scanned in opposite directions and the output from the cameras are used to drive the earphones.
U.S. Patent No. 4,000,565 to Oversee et at discloses an apparatus for converting silent digital visual display characters into sequentially enunciated audible tones which blind or visually handicapped persons can recognize.

SUMMARY OF TOE INVENTION

One object of the present invention is to provide a system which can transform electrical waveform signals into sound pattern configurations representative of the signals.

Another object of the present invention is to provide a waveform to sound pattern converter which can be used with an existing oscilloscope to produce an audible representation of the pattern displayed on the oscilloscope CRT.
A further object of the present invention is to provide a waveform to sound pattern converter which can be used to augment an oscilloscope or other measuring device to alloy field service personnel to devote their attention to manipulating the electrical probes or the like connected to the oscilloscope and still be able to determine when a desired electrical signal exists by hearing a sound pattern representing the signal.
Another object of the present invention is to provide a system which will enable a visually handicapped person to determine an electrical waveform by listening to its sound pattern.
Yet another object of the present invention is to provide a waveform to sound pattern converter which is relatively simple to use and uncomplicated in structure.
In accordance with the above and other objects, the system of the present invention produces an audible image of a time dependent signal The system comprises circuitry for digitizing the signal to produce a plurality of discrete level signals representative of the signal circuitry for producing a different audible tone signal for each level of the discrete level signals, a speaker for producing audible sounds, and driving circuitry for the speakers to produce an audibly perceptible reference frame indicative of a predetermined time duration and for driving the speaker with the audible tone signals such that the audible tone signals have the same time orientation within the reference frame with respect to each other as the discrete level signals have in the time dependent signal.
The discrete level signals can be in the form of voltage signals and the circuitry for producing different audible tone signals can be a voltage to frequency converter in the form of a voltage controlled oscillator.
In accordance with other aspects of the invention, the perceptible reference frame is a time reference frame and the speaker driving circuitry includes a reference generator for producing an audible reference signal having a period equal to the period of the time reference frame.
The system can also include a sampling circuit for sampling the time dependent signal to produce a sampled lower frequency signal in the audible range when the time dependent signal has a frequency greater than the highest audible frequency.
The sampling circuit can include a memory Z5 having a plurality of locations and circuitry for writing the discrete level signals into the memory locations at a first speed and reading information out of the memory locations at a second speed. The memory can comprise two memory units wherein information is written into one of the memory units at one of the speeds and simultaneously information is read out of the other memory unit at the other speed 'Lowe digitizing circuit can :Lnclllde both an analog to digital converter and a digital to analog converter connected to a memory, and circuitry for writing information into the memory at high speed (from -the analog -to digital converter) and reading the information out of the memory at low speed -to the digital to analog converter.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Fig. 1 is a block diagram of a firs-t embodiment of a waveform to sound pattern converter in accordance with the invention; and Fig. 2 is a block diagram of a second embodiment of a waveform to sound pattern converter in accordance with the invention.

As shown in Fig. 1 of the drawings, the waveform to sound pattern converter 10 comprises a differential amplifier 12 connected to a high speed in, low speed out memory 14 which operates in accordance with a trigger circuit 16 and a synchronization and timing circuit I to store data related to a signal received by differential amplifier 12 and read the data out at a low speed to voltage to frequency converter 20. A horizontal reference circuit 22 is connected to receive -timing signals from synchronization and timing circuit 18 and output a horizontal reference frequency. The signals from the horizontal reference circuit 22 and voltage to frequency converter 20 are received by audio output circuit 24 and converted to an audible signal. The output of memory circuit 14 can also be passed to cathode ray tube display 26 together with the horizontal reference output of circuit 22 to provide a visllal display corresponding to the audio signal output from circuit 24~
differential amplifier 12 has input lines 27 and 28 which may be, for example, connected to high and low voltage electrical probes, respectively.
Differential amplifier 12 produces an output which is free of common mode noise and it indicative of the amplitude of the signal received on lines 27 and 28.
The present invention is designed to provide an audio output which is representative of the display on an oscilloscope. accordingly, differential amplifier 12 and leads 27 and 28 can be components of an oscilloscope. In order to construct the present invention, all that need be done is that a lea be connected to the output of the oscilloscope differential amplifier.
Trigger circuit 16 can be a conventional trigger circuit found in an oscilloscope. The purpose of trigger circuit 16 is to begin each sweep of the oscilloscope display at the same point on a repetitive input signal. Trigger circuit 16 performs essentially I the same function in the waveform to sound pattern converter of the present invention and, accordingly, an oscilloscope trigger circuit can be used my simply connecting a lead to the trigger circuit output, Any high frequency input signal detected by differelltial amplifier 12 must be essentially slowed down in time in order for the waveform to sound pattern converter of the present invention to produce an audible representation of the signal. For this purpose, memory 14 is provided. Memory 14 receives the signal from differential amplifier 12 and essentially samples the signal by selecting and digitizing a predetermined proportion of signal frames and converting the digitized signal frames into analog signals. These analog signals are used to drive voltage to frequency converter 20 which can be a voltage controlled oscillator. Voltage to frequency converter 20 is set up such that the larger magnitude analog signals received produce high frequency output signals and the lower magnitude analog signals produce relatively lower frequency output signals.
Accordingly, memory 14 slows down the input signal received from differential amplifier 12 and voltage to frequency converter 20 produces an output signal the frequency of which increases as the amplitude of the slowed input signal becomes more positive and decreases as the amplitude of the slowed input signal becomes more negative.
horizontal reference circuit 22 receives timing signal from synchronization and timing circuit 18 indicating the beginning of each new frame of information transmitted from voltage to frequency converter 20 to audio output circuit 24. Horizontal reference circuit 22 produce an audio frequency signal indicative of each new frame of information.

This signal can take the form of a single burst, a variable frequency tone, a series of tones, or the like The period of this signal is equivalent to the period of the information frame which it signifies.
This reference signal is added to the signal from voltage to frequency converter 20 in audio output circuit 24~ The resultant signal is an audible erroneous signal indicating the duration of each frame of information together with a varying frequency signal indicative of the shape of the signal received by differential amplifier 12. This varying frequency signal increases and decreases in frequency to indicate more positive and less positive (or negative amplitudes respectively, of the signal input to differential amplifier 12. The relationship of each specific frequency of the varying frequency signal to the reference signal is the same as the relationship of the corresponding amplitude portion of the input signal to the display of an oscilloscope when viewed on the oscilloscope Memory 14 comprises a high speed analog to digital (A/D) converter 30 which is connected to receive the output of differential amplifier 12. AND
converter is connected through AND gate 32 to a digital first-in first-out lFIFO) memory 34. The output of memory 34 is passed through AND gate 36 to a digital to analog DOW) converter 38, the output of which is connected to voltage to frequency converter 20. Operation of AND converter 30 is controlled by synchronization and timing circuit 18 through line 40.

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Gate 32 is enabled or disabled by a signal sent from circuit 18 on line 42. Also, sequencing of FIFO
memory 34 is effected by circuit 18 through a signal on line 44~ In order to enter information into FIFO
memory 34, converter 30 is enabled m times at a high rate of speed and m outputs are passed through gate 32 and written into the m stages of FIFO memory 34 at high speed. Converter 30 and gate 32 are then disabled and gate 36 is enabled by a signal on line 46. Low speed pulses are thin applied through line 44 Jo FIFO memory 34 until all stages of memory 34 have been read out into AYE converter 38 which outputs an analog signal to voltage to frequency converter 20.
Synchronization and timing circuit 18 contains a master clock 48 which is connected to one input of AND gate 50, to all the counters DIVIDER
circuits), and to the clock input of one stage shift register 52. The second input of AND gate 50 is connected from the non-inverted output of flip flop 54 I which receives inputs from trigger circuit 16 and shift register 52. The output of AND gate 50 is connected to one input of an AND gate 56, one input of a multiplexer 58, and to the input of a programmable divide by n circuit 60. The output ox divider circuit 60 it passed to a second input of multiplexer 58. The input of multiplexer 58 from AND gate 50 comer isles a high speed input and the input f rum circuit 60 comprises a low speed input. Multiplexer 58 connects either the high or low speed inputs to output line 62 depending on thy status of a select input which is connected to line 64. Output lone 62 is connected to input line 44 of memory 34 and is also Jo 3 D~3~3 .

connected to the input of divide by m counter 66~ The output of counter 66 is connected to the input of divide-by two counter 68, the output of winch it connected to line 64 which, as discussed above, activates the select input of multiplexer 58. The output of divider 68 is also connected through line 70 to the input of horizontal reference generator 22, line 46 which, as discussed above is one input to AND
gate 36, audio output circuitry 24, and through inventor 72, to line 42 and to an input of AND gate 56 and an input of gate 32~ Divider 66 has a set of outputs which are connected through line 74 to horn-zontal reference generator 22. Also, the output of divider 66 is connected through line 76 to horizontal reference generator 22. Divider 68 also has a ripple carry output which is connected through line 78 to the reset inputs of divider 60, divider 66, divider 68, and IFFY memory 34 as well as to one input of an AND
gate 80~ Programmable divider 60 also has a ripple carry output connected to an input of AND gate 80.
The output of AND gate 80 us connected to the data input of shift register 52.
Audio output circuitry 24 includes an analog gate 82 which receives the output of voltage to frequency converter 20 and also receives an output on line 70 from divider 68. The output of analog gate 82 is connected to an analog summing circuit 84 which drives power amplifier 86 connected to audio output transducer B80 A second analog gate 90 receives the output of horizontal reference generator 22 and also .2 to receives an output on line 70 from divide by two circuit 68. The output of analog gate 90 is also passed to summing circuit 84 where it it added to the output of analog gate 82.
In operation, trigger circuit 16 begins the data conversion cycle by setting R/S flip flop 54 when it senses a predetermined position on the input signal. The output of flip flop So enables AND gate 50 50 as to pass clock pulses from master clock 48 to lo END gate 560 As long as divide by two counter 68 passes a low output through line 70, this low output is inverted to a high input in inventor 72 and enables AND gate 56 and AND gate 320 Accordingly, clock pulses from master clock 48 trigger A/D conversions in . converter 30 and these conversions are passed through AND gate 32 to digital FIFE memory 34. Line 70 is also connected to input line 46 of AND gate 36.
Accordingly, the low signal on line 7Q inhibits AND
gate 36 thus blocking the digital FIFE signals from memory 34 from being passed Jo D/A converter 38. At the same time, analog gates I and 90 are in the blocking state thus preventing any signals from reaching analog summer 84.
Converted signals from converter 30 are passed to memory 34 and Jill up the m stages of that memory. This operation is carried out at high speed due to the fact thaw the output of counter pa is passed through line 64 to the select input of multiplexer 58. A low signal on line 64 causes multiplexer I to select the high speed output from AND gate 50 and pass this output to FIFO memory 34.

Accordingly, the writing process in FIFO memory 34 is synchronized with the conversion process in converter 30 which processes are carried out at the rate of master clock 48. One count after the m stages of memory 34 are full, counter 68, which receives the high speed clock pulses divided by m from counter I
produces a high output on lines 64 and 70~ This causes multiplexer 58 to switch to the low frequency input from programmable divider 60. Divider 60 can be selected Jo produce any desirable low speed Output signal. Alternatively a separate clock could be used in place of divider 60, if properly synchronized. The low speed clock pulses from multiplexer 58 are used to read out the data which has been stored in digital FIFO 34. The low speed is used to slow down the signal to rates that can be followed by the human ear.
At the same time, gates 32 and 56. are blocked by the inverted signal on line 70 from ;nverter 72 and gate 36 it enabled to pass the data read out from memory 34 Jo D/A converter 38. The D/A converter 38 translates the digitized voltage levels back to analog voltage level which are now greatly stretched out in time.
The analog output of D/A converter 38 causes the voltage to frequency converter 20 to translate the slowed signal voltage to a data frequency. It should be noted in this regard that the input signal to differential amplifier 12 has not only been slowed down in time, but the electrical signals amplitude has now been converted to an audio frequency. This frequency is directly proportional to the amplitude and polarity of the electrical signal and is passed through analog gate 82 to summer 84. Thy horizontal reference signal from generator 22 is passed through analog gate 90, which is also enabled at this time, to summer 84. horizontal reference generator 22 produces an audio signal indicative of each frump of inform motion which is passed to the analog summer 84 from gate 82. Generator 22 can operate in various ways The simplest form of a generator would be one which Produces a low frequency reference signal for one-half of each information frame as defined Beth output of counter 65 so that a user of the device will be easily able to recognize the firs half of a frame versus the second half of a frame. Alternately, the reference sound can take the form of a signal which changes for each predetermined portion of a reference frame to divide the frame into quarters, eighths etch Accordingly, analog summer produces an output signal to power amplifier 86 which is the summation of the data signal from voltage to frequency converter 20 and the reference signal from generator 22~ this signal is amplified and output through transducer By which may be a conventional audio speaker.
When the last byte of stored date is being read out of digital FIFO 34, the ripple carry of divide by two counter 68 sends a reset signal to its own reset input, the reset input of counter I and the reset input of counter 66 as well as to the reset input of FIFO memory 34. This signal is also sent to AND gate 80 which receives a coincident ripple carry signal from counter 60. On the next count, the output of counter 68 goes low and all counters are reset to zero. At the same time, shift register 52 resets flip flop 54 and holds it in the reset mode for one clock pulse from clock 48. Now the entire system has been reset to the initial position and is ready to take additional data. The system then waits or the next trigger signal from trigger circuit 16 to start the next cycle.
The system described above contains only a single signal converter and translator. By adding a second such system, together with the proper synchronization circuitry, it is possible to obtain a continuous audio output.
The embodiment of Figure 1 has a disadvan-tare in that A/D converter 30 must be capable of performing conversions at high speed. Such converters are available but are usually expensive. Accordingly, it would be preferable to be able to use lower cost A/D converters and obtain the same result. Figure 2 shows a circuit 10' which is designed to do just that.
In circuit 10'/ components similar to those of circuit 10 are labeled with similar reference numerals. As with circuit yo-yo a differential amplifier 12 produces an output signal which is received by trigger circuit 16 and is received by a high speed it low speed out, memory circuit 14'.
Memory circuit 14' is connected Jo: voltage to frequency converter 20 which passes a frequency converted signal through analog gate By to analog summer By. Operation of memory 14' is under the control of synchronization and timing circuit 181 which also controls horizontal reference generator 22.
The output of reference generator 22 is grated through analog gate 90 to analog summer 84 where it is added to the output of gate 82.
The difference between memory circuit 14' of circuit lo and memory circuit 14 of circuit lo is that memory circuit 14' includes an m stage charge couple device fused as an analog FIFE memory) 98 lo before A/D converter 30'. FIFE 98 serves to slow down the analog signal from amplifier 12 so that converter 30' can be a low speed relatively inexpensive, converter.
In order to utilize FIFE memory 98, synchronization and timing circuit 18' is substantially more complex than circuit 18 of circuit lo Circuit 18' includes a high speed data clock 48 which is connected to a first multiplexer lo as one input to the multiplexer. The data clock output is also connected to one input of AND gate lo and to a divide by p counter Lowe Trigger circuit 16 is connected through AND gate 106 to the set input of flip flop 108. The output of flip flop -108 is connected to AN gate lo as well as to the second input of AND gate 1020 The output of AND gate 102 it connected to the input of divide by n counter 112.
The output of counter 112 is connected as a medium speed clock input to multiplexer lug and to a second multiplexer 114n The output of multiplexer 100 is connected to the clock input of FIFE 98, Jo the second input of AND gate lo and to the second input of AND
gate loo The output of AND gate lo is connected to the input of divide by m counter 118. Counter 118 has an output connected to divide by two counter 120 and also has a ripple carry output connected as one input to AND gate 122. Counter 120 has an output connected through inventor 124 to the second input of AND gate 122, and as the clock select input of multiplexer 100 as well as the second input to AND gate 116~ Counter 120 also has a ripple carry output which is connected to the reset inputs of counters 112, 118 and 120 as well as to the data input of a one count shift register 52'~ The clock input of shift register 52' is connected to the output of data clock 48~ The output of shirt register 52' is connected to the rest input of slip flop 1080 The output of AND gate 116 is connected to the enable input of converter 30'. AND gate 116 serves to pass clock pulse from multiplexer 100 to converter 30' in synchronism with the clock pulses applied to FIFE 98 when the output of counter 120 is high.
The output of AND gate 12~ is connected to the reset inputs of divide by p counter 104, divide by m counter 126~ and divide by 2 counter 128 as well as the reset input of m stage digital FIFE memory 34.
As discussed above, counter 104 receives its input from data clock 48, The output of counter 134 acts as the low speed clock input to multiplexer 114 and is also passed to horizontal reference generator 22. The output ox multiplexer 114 is connected to the clock input ox FIFE memory 34 as well as the input of I

divide by m counter 126. The output of counter 126 is Acadia to divine by 2 counter 128, the output of which is connected to the write input of FIFO memory 34, AND
gate 36, analog gate 82, analog gate 90, horizontal reference generator 22 r the clock select input of multiplexer 114, and, through inventor 130 to AND gate 106. Counter 126 also has reference lines output which are connected to horizontal reference generator 22 through line 132.
In operation, the amplified signal from differential amplifier 12 is received by m stage COD
analog FIFO memory 98 and trigger circuit 16. A soon as the trigger circuit activates flip flop 108~ divide by m counter 118 starts counting clock pulses as the analog signals enter FIFO I Aye converter 30' is not processing data during this portion of the cycle.
When divide by m counter 118 is full, its ripple carry output passes through AND gate 122 since the output of inventor 124 is still IT to reset m stage digital FIFO 34 as well a counters 126, 128 and 104, At this time, the COD FIFO 98 is full of the signal to be transformed to an audio sound pattern The next clock pulse from clock 48 causes divide by two counter 128 to go low and divide by two counter 12~ to go high. In addition, divide by m counter 118 returns to zero. This switches multiplexes 100 and 114 to the medium speed clock obtained prom the divide by n counter 112. The same signal activates AND Nate 116 allowing the medium speed clock to trigger A/D conversions once for each medium speed clock pulse. The m stage digital FIFO 34 now reads in the digitized signal from the A/D
converter 30'.

When divide by m counter 118 and divide by m counter 126 are full, all of the COD FIFE data has been digitized and stored in m stage digital FIFE 34.
At this point the divide by two counter 120 ripple carry output goes high. The beginning of the next medium speed clock pulse causes divide by two counter 128 to go high also. This causes multiplexer 114 to select the low speed clock to drive divine by m counter 126 and digital FIFE 34. This enables AND
gate 6 so that the stored data from FIFE 34 can reach the D/A converter 380 This also enables the two output analog gates 82 and 90 to open so that audio signals can reach the audio output transducer 88. to the same time, one count shift register 126 resets flip flop 108 and AND gate 106 is inhibited by the high state of divide by two counter 128.
At this point, the low speed section of the circuit transfers the data stored in m stage digital FIFE 34 to the output DOW converter 38 through AND
gate 36. DfA converter 38 translates the digital data to an analog output voltage, the amplitude of which is directly proportional to the amplitude an polarity of the electrical signal that was stored in the COD FIFE
98V and then transferred to digital FIFE 34. This analog voltage is translated, in turn, to an audio frequency by the voltage to frequency converter 20. A
zero reference frequency can be used to divide the audio output into frequencies corresponding to post-live and negative polarities. The frequency of the output signal above the Nero reference signal is directly proportional to the amplitude of the original input signal times its polarity received by differential amplifier 12.

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The voltage Jo frequency converter output in the horizontal reference output are added in the analog summer. Finally, the summed signal are amplified by the power amplifier 86 and the amplified . 5 signal is converted to an audible signal by the audio output transducer which may be a conventional loud speaker.
When the last byte of data has been read out of the digital FIFE 34, the divide by two counter 128 goes low enabling AND gate 106 again and closing the analog gates in the output section of the circuit. At this point, only the m stage COD analog IFFY 9B and the divide by P counter 104 are functioning until the next trigger signal sets the R/S flip 10p 108 into the run state.
The worst case condition which can occur during startup operation is if the slide by two counter 128 starts in the high state, flip flop 108 starts in the low state, divide by two counter 120 starts in the low state, and the divide by m counter 118 ripple carry output is high. In this condition, the divide by two counter 128 will go low on the next count and triggering will then start and operation of the circuit will continue as described above.
US If divide by two counter 128 come on high, and the circuitry is counting, divide by m counter 126 will always count until divide by two counter 128 goes low. A normal cycle will then start at this time.
A with circuit 10 Sarasota 10 1 is shown to contain only a single converter and translator. By adding a second such system, together with proper synchronization circuitry, it is possible to obtain a continuous audio output.

The foregoing description of the preferred embodiments is set forth for the purpose of illustrating the present invention but is not considered to limit the invention in any manner.
Clearly, numerous additions modifications, and other changes can be made to the present invention by one of ordinary skill in the art without departing from the scope thereof, as set forth in the appended claims

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A system for producing an audible image of a time dependent signal, comprising:
means for digitizing said signal to produce a plurality of discrete level signals representative of said time dependent signal;
means for producing a different audible tone signal for each level of said discrete level signals;
speaker means for producing audible sounds; and means for driving said speaker means to produce an audibly perceptible reference frame indicative of a predetermined time duration and driving said speaker means with said audible tone signals such that said audible tone signals have the same time orientation with respect to each other as said discrete level signals have in said time dependent signal.

2. The system as set forth in Claim 1, wherein said discrete level signals are voltage signals and said producing means comprises a voltage to frequency converter.

3. The system as set forth in Claim 1, wherein said digitizing means comprises an analog to digital converter.

4. The system as set forth in Claim 1, wherein said perceptible reference frame is a time reference frame, and said driving means includes a reference generator means for producing an audible reference signal having a period equal to the period of said reference frame.

5. The system as set forth in Claim 1, wherein said time dependent signal is a signal having a frequency higher than the highest audible frequency, and further including means for sampling said time dependent signal to produce a sample signal in the audible range.

6. The system as set forth in Claim 1, wherein said digitizing means includes a memory having a plurality of locations, means for writing values from said time dependent signal into said memory locations at a first speed and reading information out from said memory locations at a second speed.

7. The system as set forth in Claim 5, wherein said sampling means includes a memory having a plurality of locations, means for writing said discrete level signals into said memory locations at a first speed, and reading said information out of said locations at a second speed.

8. The system as set forth in Claim 7, wherein said memory comprises two memory units and said reading and writing means includes means for writing information into the locations of one of said memory units and simultaneously reading information out of the memory locations of the other of said memory units.

9. The system as set forth in Claim 1, in combination with an oscilloscope, wherein said time dependent signal is an input signal to said oscilloscope, and said oscilloscope includes a trigger circuit, wherein the operation of said digitizing means is controlled by said trigger circuit such that said system is synchronized with said oscilloscope.

10. The system as set forth in Claim 1, wherein said digitizing means comprises a memory, means for writing information into said memory at high speed and reading information out of said memory at low speed, an analog to digital converter connected to receive the output of said memory, a second memory connected to receive the output of said analog to digital converter, means for writing information into said second memory at high speed and reading infor-mation out of said second memory at low speed, and a digital to analog converter connected to receive the output of said second memory.

11. The system for producing an audible image of a time dependent signal, comprising:
input amplifier means for amplifying a received analog input signal and outputting said amplified input signal;

converter means for receiving said amplified input signal and producing a digitized output signal representative of said amplified input signal;
memory means having a plurality of memory locations;
means for writing portions of said digitized signal into said memory locations at a first rate and reading data out of said memory locations at a second rate;
converter means for receiving data read out of said memory locations and converting said data into an analog signal;
voltage to frequency converter means for receiving said analog converted signal and producing a frequency dependent signal having a frequency proportional to the amplitude of said analog converted signal; and means for producing an audible sound representation of said frequency dependent signal.