METHOD AND APPARATUS FOR DECREASING STORAGE REQUIREMENTS FOR A VOICE RECORDING SYSTEM

Abstract: A voice recording system for storing data from a two-way conversation, the system includes a microphone (160), a speaker (150), an audio device (102), an audio transmission controller (106), a storage device (110) and a switching circuit (108). The audio transmission controller has an input (120) and an output coupled to the audio device and an input (128) coupled to the microphone and an output (122) coupled to the speaker. The audio transmission controller provides a transmit detect signal, a receive detect signal and an idle detect signal in response to audio transmissions received at the audio transmission controller. The switching circuit is configured to store in the storage device only an active side of the conversation in response to the receive detect signal, the transmit detect signal and the idle detect signal.

Description: METHOD AND APPARATUS FOR DECREASING STORAGE REQUIREMENTS FOR A VOICE RECORDING SYSTEM FIELD OF THE INVENTION The present invention relates generally to voice recording systems. More specifically, the present invention relates to a method and apparatus for decreasing storage requirements of a voice recording systems. BACKGROUND Voice recording systems are used to record signals representative of speech for subsequent playback. Some such systems are analog in nature and store analog information, for example, on magnetic tape. Other systems are digital and convert analog audio information to digital form before recording digital audio data in a digital storage medium. In either an analog or a digital system, the recorded information may be retrieved and converted to signals representative of speech for audio playback. One limitation always faced by voice recording systems is the capacity of the storage medium. The system can only store as much information or data as the storage medium can contain. This problem can often be solved by increasing the capacity of the storage medium. For example, a longer magnetic tape or a larger memory can be used. However, this may not always be feasible. In some devices, such as radiotelephones, the physical size of the device is severely limited and adding more memory is not an option. Another solution involves more efficient storage of voice information, such as by compressing the data using known data compression techniques. However, audio compression may not be feasible if the required processing power is not available, or for other reasons. A further limitation arises in systems designed to record both sides of a two- way conversation. In one prior art system, the two audio channels (receive and transmit) are summed electrically. This can be accomplished, for example, using an operational amplifier on two analog audio signals. Alternatively, the two audio channels can be digitized and the resulting digital data combined. When one channel is idle while the other is active, the system stores the active channel information but adds in the idle channel noise. This noise is evident upon playback of the stored audio information and degrades the quality of the audio upon playback. Filtering of the noise may be a possibility for improving the storage or playback audio quality. However, much or most of the noise is in the same frequency band as the active channel audio and cannot be effectively filtered. Accordingly, there is a need for an improved method and apparatus for storing voice information in a voice recording system which reduces storage requirements and which minimizes degradation of audio quality by avoiding storage of idle channel noise. SUMMARY By way of introduction only, the present invention provides a voice processing system, which reduces storage requirements by storing only the active side of a two-way conversation. One embodiment monitors both sides of the conversation and determines which is the active side. Only that side is stored. If the conversation is idle during any period of time so that no side of the conversation is active, no information or data is stored during the idle time. This further reduces storage requirements for the system. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is first embodiment of a voice processing circuit; FIG. 2 is a second embodiment of a voice processing circuit; and FIG. 3 is a portion of an audio transmission controller for use in the voice processing circuits of FIG. 1 and FIG. 2. DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, it shows a block diagram of a voice processing circuit 100. The voice processing circuit 100 includes a digital audio device 102, a codec 104, an audio transmission controller 106, a processor 108 and a digital storage device 110. The voice processing circuit 100 further includes a speaker 150 and a i microphone 160 which provide an audio interface for conveying and receiving audible sound. The digital audio device 102 may be any appropriate source of digital audio data. In one exemplary embodiment, the digital audio device is a digital signal processor of a radiotelephone such as a cellular telephone. In such an application, the digital audio device conveys encoded digital data between a transmit/receive circuit (not shown) and the rest of the voice processing circuit 100. The data are encoded in a format for efficient radio transmission. Various speech coding technologies, such as Algebraic Code Excited Linear Predictive (ACELP) coding are available for this purpose. The digital audio device 102 decodes the encoded data into a form usable by the voice processing circuit 100, such as pulse code modulation (PCM) digital data representative of speech. The digital audio data received on a downlink (i.e., from a remote base station at the radiotelephone) are placed on a receive data line 112 at an output 116. Digital audio data for transmission on an uplink (to the remote base station) are received at the digital audio device 102 on a transmit data line 114 at an input 118.. The digital audio device 102 encodes this digital audio data using a suitable speech coding technique such as ACELP and conveys the encoded data to the transmit/receive circuit for radio transmission. The codec 104 is a coder and decoder of digital audio data and analog audio information. Digital audio data are received from the digital audio device 102 at an input 120 on the receive data line 112. The digital audio data are processed by the codec and analog audio information is provided at an output 122 on a receive audio line 124. The analog audio information in the illustrated embodiment takes the form of an alternating current (AC) signal suitable to drive the speaker 150 to produce audible sound recognizable as speech. Audible sound is received at the microphone and converted to analog audio information by the microphone. The analog audio information is received by the codec 104 on transmit audio line 126 at an input 128. The codec 104 encodes the analog audio information as digital audio data, for example PCM data and provides this digital audio data at an output 130 on transmit data line 114. The audio transmission controller 106 is a duplex controller for controlling data flow in a two-way communication path. In the preferred embodiment, the audio J transmission controller 106 includes a Voice Switched Speakerphone Integrated Circuit, model number TEA1095, available from Philips Semiconductors, Sunnyvale, California. Other devices or combinations of devices may be substituted and provide similar functionality. This integrated circuit in one application provides hands-free control of an audio device such as a speakerphone In the illustrated embodiment, the audio transmission controller 106 includes a transmit amplifier, a receiver amplifier and a duplex controller. The audio transmission controller 106 is coupled between the codec 104 and the speaker 150 and the microphone 160 for controlling flow of audio signals in the voice processing circuit. The audio transmission controller 106 produces control signals in response to the flow of audio signals. In a manner to be described in detail below in conjunction with FIG. 3, the audio transmission controller 106 provides control signals for controlling the operation of the processor 108. The digital audio device 102, the codec 104, the audio transmission controller 106 and the speaker 150 and the microphone 160 in combination permit the processing of a two-way conversation. Digital audio data representative of speech are produced at the digital audio device 102, for example in response to encoded speech received over a radio link. The digital audio data are conveyed over receive data line 112 to the codec 104 where the data are converted to analog audio signals. The analog audio signals are conveyed over the receive audio line 124 to the audio transmission controller 106 and on to the speaker 150 for production of audible sound, completing the path for the first side of the conversation. On the reverse side of the conversation, audible sound is received at the microphone 160 and provided as analog audio signals to the audio transmission controller 106. The analog audio signals are in turn conveyed on the transmit audio line 126 to the codec 104. The analog signals are encoded as digital audio data, such as PCM data, and communicated on the transmit data line 114 to the digital audio device 102 for subsequent transmission. This is the path for the second side of the two-way conversation. The processor 108 is coupled to the digital audio device 102 and the digital storage device 110 for storing and retrieving digital audio data in the digital storage device 110. To this end, the processor 108 has an input 132 coupled to the transmit data line 114 and an input 134 coupled to the receive data line 112. Further, the J processor 108 has a bi-directional input/output 136 coupled to the digital storage device 110 for communicating data with the digital storage device 110. The digital storage device 110 in the embodiment of FIG. 1 is preferably a semiconductor memory device, such as a memory integrated circuit. Other storage media may be substituted. The processor 108 further has an input 140, an input 142 and an input 144 coupled to the audio transmission controller 106 for receiving control signals from the audio transmission controller 106. The control signals are conveyed on a transmit detect line 152, a receive detect line 154 and an idle detect line 156. In the illustrated embodiment, the processor 108 is responsive to the control signals for storing in the digital storage device data representative of one side only of a two-way conversation. To reduce storage requirements, only the active side of the conversation is stored. The active side may be on side only of the conversation or it may be, for brief periods, both sides of the conversation. The transmit detect line 152 and the receive detect line 154 provide to the processor 108 an indication of which side of the conversation is the active side of the conversation. In response to the indication, the processor 108 suspends storage of data representative of the inactive side of the conversation and stores only data representative of the active side of the conversation. Moreover, the idle detect line 156 provides an indication to the processor 108 that the conversation is idle, with neither side being active. In response to an idle detect signal on the idle detect line 156, the processor 108 suspends storage of digital data in the digital storage device 110. Also, in the preferred embodiment, in response to the indication that the conversation is idle on the idle detect line 156, the processor 108 enters a low power mode by shutting down substantial portions of the operating circuitry of the processor 108. Since pauses in one or both sides of a conversation can be of substantial duration, the voice processing circuit 100 of FIG. 1 can substantially reduce storage requirements of the digital storage device 110. Moreover, if the processor 108 is powered down during idle times, the overall power dissipation of the voice processing circuit 100 is reduced. This is an important design goal particularly for battery- powered electronic devices such as a radiotelephone. J FIG. 1 shows an apparatus for storage of digital data representative of the two- way conversation. In most applications, manipulation and storage of digital data is preferred. Circuits including integrated circuits are well developed and for such purposes. However, in some applications, manipulation and storage of analog information may be preferable. Accordingly, FIG. 2 shows a shows a block diagram of a voice processing circuit 200. The voice processing circuit 200 includes a digital audio device 202, a codec 204, an audio transmission controller 206, an analog switch 208 and an analog storage device 210. The voice processing circuit 200 further includes a speaker 250 and a microphone 260 which provide an audio interface for conveying and receiving audible sound. The voice processing circuit 200 of FIG. 2 operates similarly to the voice processing circuit 100 of FIG. 1. The digital audio device 202 operates as a source of digital audio data, such as pulse code modulated (PCM) data. The digital audio data are conveyed over a receive data line from an output 216 of the digital audio device 202 to an input 220 of the codec 204. The codec 203 decodes the digital audio data and produces analog audio signals at an output 222 on the receive audio line 224. The analog audio signals are conveyed by the audio transmission controller 206 to the speaker. In response to the audio signals, the speaker produces audible sound. This forms the path for one side of a two-way conversation. For the other path in the two-way conversation, the microphone detects audible sound and produces analog audio signals. These analog audio signals are conveyed by the audio transmission controller 206 to a transmit audio line 226 and received by the codec 204 at an input 228. The codec encodes the analog audio signals as digital audio data, such as PCM data and conveys the digital audio data to the transmit data line 214. The digital audio device receives the digital audio data at an input 218 for subsequent processing. In this manner and similar to the embodiment of FIG. 1, the digital audio device 202, the codec 204, the audio transmission controller 206 and the speaker 250 and the microphone 260 in combination permit the processing of a two-way conversation. The audio transmission controller 206 is a duplex controller for controlling data flow in a two-way communication path. In the preferred embodiment, the audio i transmission controller 206 includes a Voice Switched Speakerphone Integrated Circuit, model number TEA1095, available from Philips Semiconductors, Sunnyvale, California. Other devices or combinations of devices may be substituted and provide similar functionality. The audio transmission controller 206 is coupled between the codec 204 and the speaker 250 and the microphone 260 for controlling flow of audio signals in the voice processing circuit 200. The audio transmission controller 206 produces control signals in response to the flow of audio signals. In a manner to be described in detail below in conjunction with FIG. 3, the audio transmission controller 106 provides control signals for controlling the operation of the analog switch 208. The analog switch 208 has an input 232 coupled to the transmit audio line 226 and an input 234 coupled to the receive audio line 224. The analog switch 208 further has an input 240 and an input 242 coupled to the audio transmission controller 206. In response to control signals received at the input 240 ' and the input 242, the analog switch 208 stores analog audio signals in the analog storage device 210. The analog switch 208 is configured to receive at an input 232 a first control signal labeled transmit detect and a second control signal labeled receive detect at an input 242. These control signals provide an indication of which side of a two-way conversation is the active side of the conversation. Thus, the analog switch 208 forms a switching circuit coupled to the digital audio device 202 and audio transmission controller 206 and configured to store in the analog storage device 210 only information representative of an active side of the conversation in response to the control signals. The analog storage device 210 may be any suitable apparatus for efficient storage of analog signals representative of audible speech. Examples include a magnetic tape or magnetic disk. The analog storage device 210 has an input 244 configured to receive a control signal labeled idle detect in FIG. 2. When both sides of the conversation are inactive or idle, the idle detect signal disables the analog storage device 210, thereby reducing storage requirements for the analog storage device 210. FIG. 3 illustrates a portion of an audio transmission controller 300 for use in the voice processing circuits of FIG. 1 and FIG. 2. The audio transmission controller 300 includes a duplex controller circuit 302, a first summer 304, a first comparator 306, a second summer 308, a second comparator 310 and a logic gate 312. The J circuit illustrated in FIG. 3 is configured to provide the control signals receive detect, transmit detect and idle detect required by the voice processing circuits of FIG. 1 and FIG. 2. The duplex controller circuit 302 is preferably a Voice Switched Speakerphone Integrated Circuit, model number TEA1095, available from Philips Semiconductors, Sunnyvale, California. Other devices or combinations of devices may be substituted and provide similar functionality. Operation of the duplex controller circuit 302 in a speakerphone application, which is different from the application of the present invention, will be described. The duplex controller circuit 302 includes two signals, a voice switch threshold (SWT) and an idle detect threshold (IDT). The voltage at SWT is derived from the circuitry inside the duplex controller circuit 302. This voltage is developed by comparing the signal envelope and the noise envelope for both channels, the receive channel and the transmit channel. By comparing these envelopes, the duplex controller circuit 302 determines whether the input signal, either the transmit signal the or receive signal, contains speech or noise. In a speakerphone application, a capacitor is attached to SWT and is charged or discharged by a current source based on the active side of the conversation. If a receive signal is detected, the capacitor for the speakerphone application is charged; if a transmit signal is detected, the capacitor is discharged. If neither a transmit or a receive signal is detected, the speaker phone capacitor is neither charged nor discharged and the voltage at SWT equals the voltage at IDT. In this state, the circuit is considered to be in idle mode. In the application illustrated in FIG. 3, the voltage at SWT is compared with the voltage at IDT. Each voltage is an analog voltage and is not related to any digital logic levels. Each voltage is applied to the summers, including first summer 304 and second summer 308. The first summer 304 subtracts the voltage SWT from the voltage IDT to produce a signal IDT-SWT. This is another analog voltage. This voltage is compared with a reference voltage at the first comparator 306 to produce a transmit detect signal on transmit detect line 152. Similarly, the second summer 308 subtracts the voltage IDT from the voltage SWT to produce a signal SWT-IDT. This voltage is applied to the second comparator 310 and compared to a reference voltage. The comparator produces a receive detect signal on receive detect line 154. In the illustrated embodiment, the reference voltage applied to both comparators is 180 mV. However, other suitable reference voltages may be chosen. The transmit detect signal and the receive detect signal are combined to produce the idle detect signal. The transmit detect signal and the receive detect signal are applied to the inputs of logic gate 312. In the illustrated embodiment, the logic gate 312 is a NOR gate, but other logic elements may be used instead, depending on the relative levels of the transmit detect signal and the receive detect signal. The output of the logic gate 312 is the idle detect signal, which is applied to the idle detect line 156. The output signals from the comparators, the transmit detect signal and the receive detect signal, are binary voltages suitable for digital logic inputs to the processor 108. Similarly, the output from the logic gate 312 is a binary voltage suitable as a digital logic input signal. The transmit detect signal is applied to input 140 of the processor 108. The receive detect signal is applied to input 142 of the processor 108 and the idle detect signal is applied to input 144 of the processor 108. In operation, the audio transmission controller 300 compares the IDT and SWT voltages, If the difference between these voltage is greater than the reference voltage, the comparators then determine whether a transmit condition exists (for example, IDT-SWT > reference voltage) or whether a receive condition exists (for example, SWT-IDT > reference voltage). If neither a transmit condition nor a receive condition exists, then the circuit indicates an idle condition. These conditions are conveyed as control signals to the processor 108. In response, the processor 108 selects a side of the conversation to convey to the storage medium for storage. In the event of the idle condition, the control signals also convey this condition and the processor 108 responds by suppressing storage of voice data or information. The audio transmission controller 300 illustrated in FIG. 3 is configured for operation with the voice processing circuit 100 with digital voice data storage illustrated in FIG. 1. The audio transmission controller 300 may be readily modified for operation in the voice processing circuit 200 of FIG. 2. From the foregoing, it can be seen that the present invention provides a method and apparatus for a voice recording system with reduced storage requirements. The system detects an active side of a two-way conversation and stores data or information corresponding only to the active side. If neither side is active, the system detects this idle condition and interrupts storage of data. In this manner, storage requirements are reduced, reducing the cost, size and current drain of the overall system. Further, in the system , the noise present on the inactive side of the conversation is not stored, reducing noise present during playback and improving audio fidelity of the overall system. While a particular embodiment of the present invention has been shown and described, modifications may be made. For example, in place of separate receive and transmit detect signals, a single binary receive/transmit signal could be provided as a control signal for indicating the active state of the two-way conversation. It is therefore intended in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention. What is claimed is:

Claims: CLAIMS 1. A voice recording method comprising the steps of: detecting a two-way conversation; identifying an active side of the conversation and an inactive side of the conversation; and recording only the active side of the conversation. 2. The voice recording method of claim 1 further comprising the step of suspending recording when both sides of the two-way conversation are inactive. 3. The voice recording method of claim 1 further comprising the steps of: selecting a first side of the two-way conversation; comparing a signal envelope and a noise envelope of the first side to determine if the first side is the active side of the two-way conversation; and comparing a signal envelope and a noise envelope of the other side to determine if the other side is the active side of the two-way conversation. 4. The voice recording method of claim 3 further comprising the step of determining that a side of the two-way conversation is inactive if amplitude of the signal envelope does not exceed amplitude of the noise envelope by a predetermined amount. 5. A voice processing circuit comprising: a digital audio device operative in response to digital audio data; a codec coupled to the digital audio device converting between analog audio signals and digital audio data; a speaker for producing audible sound in response to an analog audio signal; a microphone for producing an analog audio signal in response to an audible sound; and an audio transmission controller coupled between the codec and the speaker and the microphone for controlling flow of audio signals in the voice processing circuit, the audio transmission controller producing control signals in response to the flow of audio signals; a storage device for storing digital data; and a processor coupled to the digital audio device and the storage device for storing and retrieving digital audio data in the storage device, the processor responsive to the control signals for storing one side only of a two-way conversation. 6. The voice processing circuit of claim 5 wherein the audio transmission controller produces as the control signals one or more transmit/receive signals indicative of an active side of the two-way conversation and wherein the processor is responsive to the one or more transmit/receive signals for storing in the storage device digital audio data corresponding to the active side of the two-way conversation. 7. The voice processing circuit of claim 6 wherein the audio transmission controller produces as the control signals a receive detect signal and a transmit detect signal, the receive detect signal indicating that the active side of the two-way conversation is received from the digital audio device and the transmit detect signal indicating that the active side of the conversation is transmitted to the digital audio device. 8. The voice processing circuit of claim 7 wherein the audio transmission controller further produces as a control signal an idle detect signal when both sides of the two-way conversation are inactive. 9. The voice processing circuit of claim 8 wherein the processor does not store any digital data in response to receipt of the idle detect signal. i 10. A voice recording system for storing data from a two-way conversation, the system comprising: a microphone; a speaker; an audio device; an audio transmission controller having an input and an output coupled to the audio device and an input coupled to the microphone and an output coupled to the speaker, the audio transmission controller providing a transmit detect signal, a receive detect signal and an idle detect signal in response to audio transmissions received at the audio transmission controller; a storage device; and a switching circuit coupled to the audio device and audio transmission controller and configured to store in the storage device only an active side of the conversation in response to the receive detect signal, the transmit detect signal and the idle detect signal. 11. The system of claim 10 wherein the audio transmission controller is configured to provide the receive detect signal when audio received from the audio device exceeds audio from the microphone and to provide the transmit detect signal when audio from the microphone exceeds audio from the audio device. 12. The system of claim 11 wherein the audio transmission controller is configured to provide the idle detect signal when audio received from the audio device and audio from the microphone both are less than a predetermined threshold. 13. The system of claim 11 wherein the audio transmission controller produces a voice switch signal having a first range of values when the audio received from the audio device exceeds audio from the microphone and a second range of values when the audio from the microphone exceeds audio from the audio device and the audio transmission controller produces an idle signal, and wherein the audio transmission controller includes a comparison circuit for comparing the voice switch signal and the idle signal to produce the receive detect signal, the transmit detect signal and the idle detect signal. 14. The system of claim 13 wherein the audio transmission controller provides the receive detect signal, the transmit detect signal and the idle detect signal as binary signals suitable for the switching circuit.

Inventors: LANDS ROBERT M, LANDS, ROBERT, M.
Applicants: ERICSSON INC, ERICSSON INC.
Application year: 1999
Main classification: G10L11
IPC codes: G10L11, G10L19