WO1993013520A2

WO1993013520A2 - Memory conservation data alignment method for solid state recording

Info

Publication number: WO1993013520A2
Application number: PCT/US1992/010941
Authority: WO
Inventors: Alexander Michael Malinsky; Daniel Corey Wiggins; Talarek Wieslaw; Robin Patrick Beaudoin
Original assignee: Sundstrand Corporation
Priority date: 1991-12-17
Filing date: 1992-12-16
Publication date: 1993-07-08
Also published as: WO1993013520A3

Abstract

A recording system (20) and process minimizes the storage capacity for recording multi-channel data into the memory space normally allocated to a single channel for a predetermined time period without compressing the data. In order to enable the data to be correlated with either real or relative time, the data is recorded along with its channel number and stored sequentially in an electronic memory (48) in predetermined time increments. Additionally, the channel activity is monitored and stored. By recording the channel number with the data and identifying the periods of channel activity, the recording data can be correlated with the time during which it was recorded. The recorded apparatus in accordance with the present invention is particularly well suited for minimizing memory requirements for recording multi-channel sequential data, such as in certain voice communications, as well as simplex and half duplex communications even in situations where there is some overlap in channel activity without the use of data compression.

Description

MEMORY CONSERVATION DATA ALIGNMENT METHOD FOR SOLID STATE RECORDING FIELD OF THE INVENTION The present invention relates to a recording system and process for recording multi-channel data, such as voice data, which minimizes the storage capacity requirements and more particularly to a recording system for recording multi-channel data into the same memory space normally allocated to a single channel for a predetermined time period without compressing the data.

BACKGROUND OF THE INVENTION 1. Description of the Prior Art

Multi-channel recording systems are generally known in the art. Such systems are generally used to record voice communications as well as other data in a variety of applications. For example, U.S. Patent Nos. 4,012,784 and 4,958,367 disclose multi-channel recording systems for recording various voice communications, such as emergency voice coinmunications in fire and police stations. The systems disclosed in these patents relate to magnetic tape type recording systems which record the voice communications, along with the time during which the communication was made. Although such systems perform adequately in many applications, a substantial portion of memory is used during periods when one or more communication channels are inactive. More specifically, magnetic tape recording systems normally utilize magnetic tape with multiple tracks; wherein each track is dedicated to a communication channel. For example, each of the emergency telephone lines into a police or fire station may be correlated to a track on the magnetic tape in order to allow simultaneous recording of voice communications. However, in such applications, all of the communication channels are generally not active at any given time. Moreover, there are other known applications used primarily for sequential communications. For example, known cockpit voice recorders (CVR) utilized in aircraft generally include four channels. One channel is dedicated to an area microphone within the cockpit which is on all the time. The other three channels are used to record communications between the pilot, co-pilot and second officer. Since the communication channels for the pilot, co-pilot and second officers are for communications which are generally sequential, only one of such communication channels is normally active at a given time. Thus, a substantial portion of magnetic tape is used in such applications while several of the communication channels are inactive.

FIG. 1 illustrates an exemplary graphical representation of the channel activity on a multi¬ channel CVR. Channel 1 corresponds to the area microphone. Channels 2, 3 and 4 correspond to the communication channels of the pilot, co-pilot and second officer, respectively. The shaded portions of the figure indicate the time during which each channel is active. For example, as illustrated, channel l is active all of the time since channel 1 is assigned to the area microphone. However, the balance of the channels (e.g., channels 2-4), assigned to the pilot, co-pilot and second officer, respectively, are only sequentially active. With such an arrangement because of the sequential nature of the communications, the composite amount of memory space required for channels 2-4 will be about the same or less than the amount of memory space normally allocated for a single channel. Accordingly, much of the memory space for channels 2-4 is wasted in known CVR's during periods of channel inactivity which results in significantly larger memory space for channels 2-4 than actually required.

There are various other problems associated with magnetic tape type recording apparatus. For example, such magnetic type recording apparatus are relatively large in size and are therefore not suitable in certain types of applications where space is relatively limited, such as in the cockpit of an aircraft. Another problem with such magnetic tape type recording apparatus is that such apparatus include a tape transport assembly which has a plurality of moving parts which are thus subject to wear and failure.

Another problem with such magnetic tape type recording apparatus relates to the electrical power requirements for the tape transport assembly. More specifically, such tape transport assemblies generally include spindle motors which require a considerable amount of electrical power. Although the electrical power requirements for a recording apparatus may not be a consideration in certain applications, there are other applications whereby electrical power requirements must be kept to a minimum, such as in an aircraft. Consequently, there has been a trend toward use of electronic memories which obviate the problem of wear and failure due to moving parts as well as reduce the electrical power requirements. In addition, such electronic memory generally takes up less space than a corresponding amount of magnetic tape memory and consequently is more adaptable in applications where space is critical.

Electronic memories have been known to be used in a number of applications. For example, U.S. Patent Nos. 4,409,670; 4,646,241; and 4,660,145 relate to the use of electronic memory for recording aircraft flight data. However, in order to conserve memory, which can be relatively expensive, such systems generally teach the use of data compression for minimizing the amount of electronic memory required. While data compression techniques may be acceptable in some applications, for example, aircraft flight data applications, such techniques are generally not acceptable in various other applications where data compression is either not desirable or allowable, such as in applications for recording cockpit voice communications. Accordingly, electronic memory allocations for multi-channel systems in such applications, often suffer the same problem as the corresponding magnetic tape recording systems discussed above. More specifically, FIG. 2 illustrates the memory mapping for a known four channel CVR which utilizes electronic memory. The memory allocated for each of the channels 2, 3 and 4 for recording voice communications among the pilot, co-pilot and second officer is equal to the memory allocation for channel 1, which corresponds to the area microphone, which is on all the time. If each channel is allocated N megabits of memory space, then a total of 4N megabits is required for the four channels. In this situation, similar to the magnetic tape application, a significant amount of memory allocation is wasted based during periods of inactivity of the various communication channels as illustrated in FIG. 1. The wasted portion of the electronic memory for each channel utilized during periods of channel inactivity significantly increases the cost of the recording apparatus as well as increases the electrical power requirements of the system.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems associated with the prior art.

It is another object of the present invention to conserve memory in a recording apparatus without compressing data. It is a further object of the present invention to provide a recording system for recording multi-channel data in the memory space normally allocated for a single channel. Briefly, the present invention relates to a recording system and process which minimizes the memory capacity for recording multi-channel data, such as voice data. In order to enable the data to be correlated with either real or relative time, the data is correlated along with its channel number and stored sequentially in an electronic memory in predetermined time increments. Additionally, the channel activity is monitored and stored. By recording the channel number with the data and identifying the periods of channel activity, the recorded data can be correlated with the time during which it was recorded. The recording apparatus in accordance with the present invention is particularly well suited for minimizing memory requirements for recording multi-channel sequential data, such as in certain voice communications, as well as simplex and half duplex communications even in situations where there is some overlap in channel activity without the use of a data compression.

BRIEF DESCRIPTION OF THE DRAWING These and other objects of the present invention will be readily apparent by reference to the following description and attached drawing, in which: FIG. 1 is an exemplary diagram illustrating channel activity for a predetermined time period for a four channel communication system wherein the shaded portions indicate periods of channel activity;

FIG. 2 is a diagram illustrating the memory mapping for a known CVR which utilizes an electronic memory; FIG. 3 is a block diagram of a multi-channel recording apparatus in accordance with the present invention; and FIG. 4 is a digital representation of the channel activity record of FIG. 1.

DETAILED DESCRIPTION A recording system in accordance with the present invention is illustrated in FIG. 3 and identified with the reference numeral 20. The recording system 20 is adapted to record multi-channel data, such as voice data, along with the time period during which each data channel is active in order to enable the data on each channel to be correlated with relative or real time. The recording system 20 is adapted to be utilized with data channels which are alternately active, such as simplex or half duplex communication channels or full duplex voice channels which, by their nature, are not continuously overlapping, such as in the case of sequential voice channels; for example, between a pilot, co-pilot and second officer in the cockpit of an aircraft, as shown in FIG. 1. The recording system 20 is also adapted to record data where there is some overlap in channel activity as will be discussed below.

In known applications of multi-channel recording systems, for example, as shown in FIG. l, a substantial amount of memory space is used during periods of channel inactivity. More specifically, such known systems are adapted to provide a simultaneous recording of all channels. Accordingly, the amount of memory space allocated for each channel is generally selected to allow for recording of data over a given period of time which assumes that each communication channel is continuously active over the selected time period. Thus, with reference to FIG. 1, the memory allocation for each of the channels 1-4, would be selected, for example, as N megabits, wherein N megabits is adapted to store all data on a given channel for a predetermined time period assuming that channel is continuously active during that entire time period. Thus, as shown in FIG. 2_Λ known multi-channel recording systems would thus allocate N megabits for each of the channels resulting in a memory allocation of 4N Mbits for the four channel system. In applications where the data channels in a multi-channel recording system are not continuously active over the entire time period, this results in wasted memory space corresponding to periods of inactive channel activity. More specifically, referring to FIG. 1, the unshaded portions of the channel activity record represent periods of channel inactivity. Since the memory allocation for each channel is predicated upon each channel being continuously active over the entire time period, these unshaded portions of the channel activity diagram are representative of wasted memory space in known multi- channel recording systems as discussed above. In such known applications, the wasted memory not only adds to the cost of the recording system but also adds to the size and the electrical power requirements of the system which is undesirable in certain applications where size and power requirements are critical, such as in an aircraft.

In some known recording systems, memory space has been minimized through the use of data compression techniques, for example, as disclosed in U.S. Patent No. 4,409,670. Although data compression techniques are useful in reducing the amount of memory space required for recording data, such data compression techniques are rather complicated and are not permissible in certain applications, such as a CVR. In these applications where data compression is not utilized, memory space is allocated to record data on a given channel assuming that the channel is active over an entire time period as discussed above.

The recording system 20 in accordance with the present invention solves these problems without the use of data compression. More specifically, the recording system 20 in accordance with the present invention is adapted to record multi-channel data in the memory space normally allocated to a single channel. Thus, referring to the example illustrated in FIGS. 1 and 2, the data in channels 2, 3 and 4 is thus stored in the memory space normally allocated for a single channel, for example, N megabits. As previously discussed, in known applications, N megabits are allocated for each of the three channels resulting in 3N megabits for channels 2- 4. Thus, the recording system 20 in accordance with the present invention results in a saving of 2N megabits of memory space for the three channels or a 66% savings without utilizing data compression.

It is to be understood by those of ordinary skill in the art that although the invention will be described and illustrated in terms of a four channel

CVR, the principles of the invention are applicable to various types of multi-channel recording systems and are not limited to an application of a CVR or any particular number of channels. Moreover, as will be discussed below, it will also be understood by those of ordinary skill in the art that the principles of the invention are applicable to analog as well as digital recording systems and is not limited to voice communication systems. Referring to FIG. 3, the recording system 20 in accordance with the present invention is illustrated and described for an application of a four channel CVR. In such an application, it is assumed that channel 1 is assigned to an area microphone 32 within the cockpit while channels 2-4 are assigned to a pilot microphone 34, a co-pilot microphone 36 and a second officer microphone 38, for example. As is known in the art, area microphones 32 within an aircraft must continuously monitor all audio activity within the cockpit. Thus channel 1 is continuously active. The channel activity associated with channels 2-4 for the pilot microphone 34, co-pilot microphone 36 and a second officer microphone 38 is assumed to be as illustrated in FIG. 1. Although such communications between the pilot, co-pilot and second officer may be full duplex, such communications are generally sequential in nature with only occasional overlapping, if any, and also includes periods during which there is absolutely no communication.

In such an application, it is necessary to correlate all communications on channels 1-4 with the time during which the communication was recorded. Thus, a channel activity record as illustrated in FIG. 4, is maintained by the recording system 20 for a predetermined time period. For illustration purposes only, this predetermined time period is assumed to be two hours or 7200 seconds which was selected to correspond to the length of a time during which the channels are active. As will be appreciated by those of ordinary skill in the art, the time period selected is dependent upon the particular application. For example, the time period for a CVR is selected to correspond to the length of time that the communication channels 1-4 will contain information relevant to an incident, for example, two hours immediately preceding the incident during which the pilot, copilot and second officer are within the cockpit of an aircraft.

Referring to FIG. 4, channel activity records 40, 42, 44 and 46 are recorded for channels 1-4 which correspond to the channel activity illustrated in FIG. 1. Each channel activity record 40, 42, 44 and 46 corresponds to the entire time period during which the recording system 20 is active, which by way of example, is assumed to be 7200 seconds as discussed above. Each channel activity record 40, 42, 44 and 46 is broken down into smaller time periods, which, as will be discussed below, correspond to the time increments in which the data is stored. By way of illustration and example, the smaller time periods illustrated in FIG. 4 are assumed to be one second. Thus, the channel activity records 40-46 as illustrated, are adapted to provide channel activity information in increments of one second. In a digital implementation of the recording system 20 in accordance with the present invention, periods of channel activity may be designated with a logical 1 while periods of channel inactivity may be designated by a logical 0. These channel activity records 40-46 are mapped into a main memory 48 into sequential address space separate from the data or voice communications as illustrated in FIG. 3.

Assuming that the channel activity records 40, 42, 44 and 46 are broken down into one second intervals, 7.2 kilobits corresponding to 7200 seconds are thus required for each channel activity record 40, 42, 44 and 46 in the memory 48 using the exemplary values discussed above. In a CVR application, since the area microphone 32 is on continuously, the channel activity record 40 for channel 1 which corresponds to the area microphone 32 can be eliminated to further reduce memory space requirements since the channel activity record 40 would appear in memory as a continuous series of logical l's. Thus, the total memory space for the four channel activity records 40, 42, 44 and 46 in such an application can be condensed to 21.6 kilobits.

In order to allow the data (e.g., voice communications) on each channel to be correlated with its corresponding channel activity record, the channel number is recorded with the data. More specifically, for a four channel system, two bits are required to identify each of the four channels. Thus, two bits per second for a total of 7200 seconds are required for each channel or a total of 57.6 Kbits. In order to allow correlation with the channel activity records 40, 42, 44 and 46, the digitized voice data along with the channel number must be stored sequentially in the memory 48 in the same time intervals selected for the channel activity records 40, 42, 44 and 46. Thus, assuming the channel activity records 40, 42, 44 and 46 are stored in increments of one second as discussed above, the digitized voice data along with its channel number are stored in the same time increments.

The memory space for the channel activity records (e.g., 21.6 Kbits) as well as the memory space required for keeping track of the channel number constitute a relatively small portion of the memory space required. More specifically, the total memory space required for marking the channel number and maintaining the channel activity records would be 79.2 Kbits (e.g., 57.6 + 21.6 Kbits). Assuming that the voice data is digitized at the rate of 16 Kbits per second, the memory required for 7200 seconds would be 115,200 Kbits per channel assuming each channel is continuously active over the entire time period (e.g., 7200 seconds) . In accordance with the present invention, a total of 115,200 Kbits would be allocated for all three of the channels 2-4. Since the memory required for the channel number and channel activity record amounts to only about .07% of the memory required for storing the voice communications, the total memory space provided can be equal to the memory required for storing the voice communications alone, since there will realistically be periods where all three channels are inactive relatively longer than .07% of the time which would account for the memory space required for the channel marking and channel activity records as well as accommodate anticipated infrequent periods where there is overlapping channel activity.

Referring to FIG. 3, an important aspect of the invention relates to the fact that the data on each of the four channels is buffered by buffer devices 50, 52, 54 and 56 before it is stored in a main memory 48. This allows any slight overlapping in the communication channels to be recorded. Moreover, the buffers 50, 52, 54 and 56 allow the channel number to be added to the digitized voice communications prior to being transferred to the main memory 48.

The size of the buffers 50, 52, 54 and 56 is selected to buffer voice communications for the incremental time period selected for the channel activity records 40, 42, 44 and 46, for example, one second or other time period which takes into consideration the amount of time to digitize and encode the voice communications with the channel number. The buffers 50, 52, 54 and 56 are preferably first in, first out (FIFO) buffers. Circuitry is also included within the logic blocks, identified with the reference numerals 50, 52, 54 and 56, for formatting the channel number relative to the digitized voice data. Although not critical to the practice of the present invention, the two bit channel number may be formatted in various ways with the digitized voice data. For example, each one second increment of voice data may be identified with the two bit channel number either at the beginning or at the end of the digitized voice data. Various means are known within the art for adding bits, such as bits corresponding to a channel number, to a bit stream. For example, asynchronous data communication systems include various start and stop bits which are added to a bit stream.

In operation with reference to FIG. 3, voice communications on each of the channels from the microphones 32, 34, 36 and 38 are filtered and amplified by the filter/amplifiers 58, 60, 62 and 64. The output of the filter/amplifiers 58, 60, 62 and 64 are applied to encoders 66, 68, 70 and 72, respectively. In a digital implementation of the recording system 20, the encoders 66, 68, 70 and 72 include analog-to-digital converters (ADC) for converting the analog voice communications to corresponding digital values. The channel number information is then added to the digitized voice data in any of a number of known ways as discussed above. However, as will be discussed below, the present invention also contemplates the use of new solid state analog memory storage systems. Consequently, in such applications, ADCs would not be required.

In order to detect channel activity, the outputs of the amplifiers 60, 62 and 64 are applied to a channel activity detector 74 in order to generate the channel activity records illustrated in FIG. 4. The channel activity detector 74 may be simple comparators for providing a logical 1 output on each channel to indicate channel activity. In the present example, since the area microphone is on all the time, as illustrated in FIG. 4, there would be no need to apply the output of the filter amplifier 58 for channel 1 to the channel activity detector 74 in order to conserve memory.

The output of the channel activity detector 74 for the channels 2-4 may be applied as either l's or 0's to a designated section of the memory 48 under the control of a controller 76. As previously discussed, since the channel activity records are memory mapped and the voice communications are marked with the channel number, this enables each voice communication to be aligned on a relative time basis relative to the other channels.

The controller 76 may include a real time clock integrated circuit, such as a Dallas Semiconductor Model PS 1286 or a Motorola type 68HC6821 integrated circuit in conjunction with a Motorola type 68HC11 microcontroller to enable each of the voice communications on channels 1-4 to be correlated with real time in a similar manner as records on a word processing system. An example of the use of such hardware is disclosed in an article entitled, ADDING A REAL TIME CLOCK, by Jan Axelson, pages 26-35, COMPUTER CRAFT MAGAZINE, November 1991, hereby incorporated by reference.

In a digital implementation, the voice communications are digitized by the encoders 66, 68, 70 and 72 in a known manner utilizing an analog-to-digital converter (ADC) . The digitized voice data is then applied to the buffer devices 50, 52, 54 and 56, respectively, wherein each voice communication is encoded with the two bit channel number under the control of the controller 76 in a known manner. Once the voice communications have been encoded with the channel number, the encoded data is then sequentially written to the memory 48 every second, for example, where it is stored for later retrieval. The system also includes a plurality of decoders 78, 80, 82 and 84, which, in a digital implementation, would include digital-to-analog converters (DAC) for decoding the digitized voice data under the control of the controller 76 and aligning the data with the channel activity records 40, 42, 44, 46 to allow playback through speakers 86, 88, 90 and 92 by way of filter amplifiers 94, 96, 98 and 100, respectively. Since the digitized voice data is sequentially stored along with its corresponding channel number in segments which correspond to the same segments of the channel activity records 40, 42, 44 and 46, the controller 76 is thus able to align the data with the channel activity records 40, 42, 44 and 46 to allow the data stored in the memory to be played back in a manner which corresponds to the time such communications were recorded. Also, as previously mentioned, the controller 76 could be provided with a real time clock integrated circuit which would enable the voice communications to be correlated with real time, for example, in a manner similar to an aural time stamp utilized on various known telephone answering machines. The present invention also contemplates the use of analog solid state memory systems, such as the new analog electronically erasable programmable read only memories (EEPROMS) . Examples of such analog memory devices are discussed in detail in IC HOLDS 16 SECONDS OF AUDIO WITHOUT POWER, by Frank Goodenough, pages 39-44 of ELECTRONIC DESIGN magazine, January 31, 1991 and HERE COMES ANALOG MEMORY, by Bill Arnold, pages 1 and 38 of EDN magazine, February 7, 1991, hereby incorporated by reference.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

What is claimed and desired to be secured by Letters Patent of the United States is:

Claims

1. A method for recording and playing back multi-channel data comprising the steps of: (a) buffering the data received on each channel; (b) identifying the data with a channel number; (c) identifying the time during which each channel is active forming a channel activity record; (d) storing the data and its respective channel number in a memory; and (e) storing the channel activity record in a memory.

2. A method as recited in claim 1, further including the step of converting the data to a corresponding digital value.

3. A method as recited in claim 1, further including the step of encoding the data with its respective channel number prior to storing said data.

4. A method as recited in claim 1, wherein said data is stored in a predetermined portion of memory.

5. A method as recited in claim 4, wherein said channel number is stored along with, the respective data in said predetermined portion of said memory.

6. A method as recited in claim 5, wherein said channel activity record is stored in a portion of said memory other than said predetermined portion.

7. A method as recited in claim 1, further including the step of storing the time during which said data is received.

8. A method as recited in claim 1, wherein said memory provided for said multi-channel data is sized to correspond the memory size of a single continuously active channel for a predetermined time period.

9. A method as recited in claim 1, further including playing back the data along with the time during which said data was received.

10. A method as recited in claim 1, further including the step of: (f) retrieving data for each channel by locating data with appropriate channel and time identification.

11. A method as recited in claim 9, further including the step of: (g) regenerating the retrieved data into the original input data by converting the retrieved data.

12. A method for recording data on multi- channels comprising the steps of: (a) identifying the channel number of the data received from each of said multiple channels; (b) recording data received from said multiple channels in a solid state memory; and (c) maintaining a channel activity record for identifying the time during which each channel is active

13. A method as recited in claim 12, further including the step of storing the channel number of the data received on each channel.

14. A method as recited in claim 12, further including the step of storing data received simultaneously from a plurality of channels.

15. A method as recited in claim 12, further including buffering the data received from said multiple channels.

16. A method as recited in claim 12, wherein said memory is an analog type memory.

17. A method as recited in claim 12, wherein said memory is a digital type memory.

18. A recording and playback apparatus for recording and playing back data on a plurality of channels comprising: means for receiving predetermined type of data on a plurality of channels; means for identifying the time during which each channel is active; and first means responsive to said receiving means and said identifying means for storing said data along with the time during which each channel is active.

19. A recording and playback apparatus as recited in claim 18, further including means for identifying the channel number of all data received by the receiving means.

20. A recording and playback apparatus as recited in claim 19, further including second means responsive to said identifying means for storing the channel numbers.

21. A recording and playback apparatus as recited in claim 18, wherein said predetermined type of data is analog data.

22. A recording and playback apparatus as recited in claim 21, wherein said analog data includes voice communications.

23. A recording and playback apparatus as recited in claim 18, wherein said predetermined type of data is digital data.

24. A recording and playback apparatus as recited in claim 18, further including means for recording data received simultaneously on two or more channels.

25. A recording and playback apparatus as recited in claim 24, wherein said recording means includes means for buffering data received on one or more of said multiple channels.

26. A recording and playback apparatus as recited in claim 18, wherein said first storing means includes a solid state memory having a predetermined size.

27. A recording and playback apparatus as recited in claim 26, wherein said predetermined size is determined in accordance with the amount of data that can be stored for a single channel in a predetermined time period.

28. A recording and playback apparatus as recited in claim 18, further including means for playing back said recorded data.

29. A recording and playback apparatus as recited in claim 28, wherein said playing back means includes means for retrieving data for each channel along with the time during which said data was recorded.

30. A recording apparatus for recording multiple channel data comprising: means for receiving data on a plurality of channels; and means for storing said data in a predetermined amount of memory space selected to correspond to the amount of data that said data which can be stored for a single channel in a predetermined time period.

31. A recording apparatus as recited in claim 30, further including means for storing data received simultaneously on a plurality of said channels.

32. A recording apparatus as recited in claim 30, wherein said storing means includes means for buffering data on one or more of said channels.

33. A recording apparatus as recited in claim 32, further including means for identifying the channel number of the data.

34. A recording apparatus as recited in claim 33, further including means for identifying the channel number or the data received on one or more of said channels.

35. A recording apparatus as recited in claim 34, further including means for encoding said data with said channel number prior to storing said data.

36. A recording apparatus as recited in claim 30, further including means for identifying the time during which channel is active.

37. A recording apparatus as recited in claim 30, further including means for correlating the real time during which said data was received.

38. A recording apparatus as recited in claim 30, wherein said storing means includes a solid state memory.

39. A recording apparatus as recited in claim 38, wherein said solid state memory is a digital memory.

40. A recording apparatus as recited in claim 38, wherein said memory is an analog memory.

41. A recording apparatus as recited in claim 34, further including means for encoding the data with channel numbers and storing said data with said channel number.

42. A recording apparatus as recited in claim 30, further including means for playing back said recorded data.

43. A recording apparatus as recited in claim 42, wherein said playing back means includes for playing back said recorded data along with its respective channel number.

44. A recording apparatus as recited in claim 43, wherein said playing back means includes means for playing back said recorded data along the time during which said recorded data was recorded.

45. A cockpit voice recorder for recording multiple channel voice communications in an aircraft comprising: means for receiving voice communications on a plurality of channels; and means for storing said voice communications in the memory space required for a single channel for a predetermined time period.

46. A cockpit voice recorder as recited in claim 45, wherein said storing means includes a solid state memory.

47. A cockpit voice recorder as recited in claim 45, further including means for correlating said voice communications with real time.

48. A cockpit voice recorder as recited in claim 45, further including means for recording overlapping voice communications.

49. A cockpit voice recorder as recited in claim 48, wherein said recording means includes means for buffering said voice communications.

50. A cockpit voice recorder as recited in claim 45, further including means for identifying and storing the channel number of the data received from each of said plurality of channels.

51. A cockpit voice recorder as recited in claim 50, further including means for storing the time during which said data is received.

52. A cockpit voice recorder as recited in claim 51, further including means for playing back said recorded data.

53. A cockpit voice recorder as recited in claim 52, wherein said playing means includes means for playing back said recorded data along with its respective channel number.

54. A cockpit voice recorder as recited.in claim 53, wherein said playing back means includes means for playing back said data along with the time during which said data was recorded.