Abstract:
A fully backward compatible intelligent discontinued transmission (DTX) and comfort noise generation (CNG) scheme that is operable in pulse code modulation (PCM) speech coding systems. The scheme, for example, provides a speech encoder comprising a speech signal analysis circuitry configured to calculates a predetermined plurality of parameters from the speech signal, a voice activity detector configured to determine voice activity in the speech signal, where the speech encoder enters a discontinued transmission mode of the voice activity detector does not detect voice activity, and a transmitter configured to transmit one or more speech samples of the speech signal after the speech encoder enters the discontinued transmission mode, where the one or more speech samples are capable of use by a remote speech decoder to extract a parameter from the one or more speech samples in order generate a background noise base on the parameter.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates generally to speech coding; and, more particularly, it relates to discontinued transmission and comfort noise generation within pulse code modulation (PCM) type of speech coders. 
     2. Related Art 
     Conventional methods of performing discontinued transmission (DTX) mode speech coding typically employs only energy level detection of background noise. That is to say, a single measure of the energy level is detected in an encoder circuitry of a speech codec, and an energy level flag is transmitted across a communication link to a decoder circuitry of the speech codec. At the decoder circuitry of the speech codec, some form of speech signal generation is performed after having received this energy level flag during the inception of discontinued transmission (DTX) modes of operation. Examples that are used to perform this comfort noise generation (CNG) in the art include utilizing a randomly selected or randomly generated sequence in a PCM coder (like the μ-Law/A-Law PCM G.711), and employing the randomly selected or the randomly generated codevector within a code-excited linear prediction (CELP) speech reproduction circuitry (like G.729 Annex B), to generate comfort noise at the decoder circuitry during discontinued transmission (DTX) modes of operation. 
     However, using this single dimensional method of encoding the background noise (energy level) of speech coding system fails to provide a high perceptual quality of reproduced background noise at the decoder circuitry of the speech codec. For example, the conventional method of employing the energy level alone simply does not provide the high perceptual quality of background noise that users of speech coding system expect. 
     One proposed method of ensuring a high perceptual quality of the coding of background noise in speech coding systems is to measure and transmit both a frequency spectrum and an energy level of a speech signal and transmit that information from the encoder circuitry to the decoder circuitry of the speech codec. One difficulty presented with the conventional methods that measure and transmit both the frequency spectrum and the energy level of the speech signal is that they inherently require a modification of the existing transmission protocols and standards. There is an inherent inability in such proposed solutions to be operable with the existing transmission protocols and standards. An entirely new silence insertion description (SID) standard would need to be designed to be able to interface with the conventionally proposed speech coding methods that are capable of ensuring a high perceptual quality of background noise within speech signals. 
     For example, the proposed conventional methods that measure and transmit both the frequency spectrum and the energy level of the speech signal inherently require the entirely new silence insertion description (SID) standard to be able to comply with and perform conventional speech coding operations such as discontinued transmission (DTX). To provide comfort noise generation (CNG) and other desirable speech coding methods that are operable to provide a high perceptual quality for applications such as speech coding of music, comfort noise generation (CNG), and other perceptual improvements that provide for increased quality for users would intrinsically require additional transformation to comply with existing speech coding standards. To provide this additional functionality, the inherently increased complexity of the overall speech coding system would result in a significant increase in size and cost. While there does exist a desire among those skilled in the art of speech coding, the presently conventional proposed methods, in that they do provide for improved perceptually quality of such speech signal elements such as background noise, they do not provide for operability with conventional transmission protocols, particularly those employing pulse code modulation (PCM). 
     Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings. 
     SUMMARY OF THE INVENTION 
     Various aspects of the present invention can be found in a speech codec that performs discontinued transmission on a speech signal having a background noise. The speech codec contains, among other things, an encoder circuitry and a decoder circuitry communicatively coupled via a communication link. The encoder circuitry is operable to receive the speech signal having the background noise. The encoder circuitry itself contains, among other things, a background noise detection circuitry that detects a frequency spectrum and an energy level corresponding to the speech signal and a transmission resuming circuitry that operates cooperatively with the background noise detection circuitry to determine when to resume transmission of the speech signal. The decoder circuitry generates a reproduced speech signal that is substantially comparable to the speech signal. The decoder circuitry itself contains, among other things, a background noise reproduction circuitry that employs a predetermined number of relatively recently received speech samples to assist in the generation of a reproduced background noise that is itself contained within the reproduced speech signal. The reproduced background noise is substantially comparable to the background noise within the speech signal. The communication link is operable using a number of transmission protocols including conventional transmission protocols. 
     In certain embodiments of the invention, the background noise reproduction circuitry further contains a frequency spectrum derivation circuitry that re-synthesizes frequency spectrum for the reproduced speech signal and an energy level change derivation circuitry that re-synthesizes an energy level for the reproduced speech signal. The background noise detection circuitry further contains a frequency spectrum change detection circuitry that detects a change in the frequency spectrum corresponding to the speech signal, and an energy level change detection circuitry that a detects a change in the energy level corresponding to the speech signal. Furthermore, the encoder circuitry further contains an intelligent discontinued transmission circuitry that operates cooperatively with the background noise detection circuitry to detect the change in the frequency spectrum corresponding to the speech signal and the change in the energy level corresponding to the speech signal. This information is used to determine when to resume transmission of the speech coding on the speech signal. 
     In other embodiments of the invention, the encoder circuitry further contains a systematic discontinued transmission circuitry that resumes transmission of the speech coding on the speech signal at time intervals determined beforehand. The predetermined number of relatively recently received speech samples is a frame of the speech signal. The predetermined number of relatively recently received speech samples includes a frequency spectrum corresponding to the predetermined number of relatively recently received speech samples and an energy level corresponding to the predetermined number of relatively recently received speech samples. 
     Other aspects of the present invention can be found in a speech codec that performs an intelligent discontinued transmission speech coding on a speech signal. The speech codec contain, among other things, a speech signal analysis circuitry that calculates a predetermined number of parameters from the speech signal and a background noise detection circuitry that detects a change of at least one of the predetermined number of parameters that is calculated from the speech signal using the speech signal analysis circuitry. The speech codec resumes transmission of a speech coding on the speech signal upon the detection of the change of the at least one of the predetermined number of parameters. 
     In certain embodiments of the invention, the predetermined number of parameters from the speech signal comprises a frequency spectrum and an energy level of the speech signal. The change of the at least one of the predetermined number of parameters is detected when the background noise detection circuitry compares the change against a predetermined threshold. 
     If desired, the speech codec further contains an encoder circuitry, a decoder circuitry, and a communication link that communicatively couples the encoder circuitry and the decoder circuitry. The transmission of the speech coding on the speech signal, performed upon the detection of the change of the at least one of the predetermined number of parameters, is resumed across the communication link. The encoder circuitry further contains an intelligent discontinued transmission circuitry that operates cooperatively with the background noise detection circuitry to detect the change of the at least one of the predetermined number of parameters that is calculated from the speech signal using the speech signal analysis circuitry. 
     In other embodiments of the invention, the encoder circuitry further contains a systematic discontinued transmission circuitry that resumes transmission of the speech coding on the speech signal at predetermined time intervals. The speech signal comprises a background noise, and the speech codec produces a reproduced speech signal wherein the reproduced speech signal contains a reproduced background noise. The reproduced background noise is substantially indistinguishable from the background noise contained within the speech signal. The speech codec re-synthesizes the background noise using a predetermined number of speech samples corresponding to the speech signal, and the predetermined number of speech samples are a relatively recently sampled number of speech samples corresponding to the speech signal. 
     Other aspects of the present invention can be found in a method that performs discontinued transmission on a speech signal. The method includes discontinuing transmission of a speech signal, detecting a change in a frequency spectrum of the speech signal, detecting a change in a energy level of the speech signal, and resuming transmission of the speech signal upon detection of at least one of the change in the frequency spectrum of the speech signal and the change in the energy level of the speech signal. 
     In certain embodiments of the invention, the method further includes resuming transmission of the speech signal upon detection of both the change in the frequency spectrum of the speech signal and the change in the energy level of the speech signal. The method further includes re-synthesizing a number of speech samples using a relatively recently sampled number of speech samples. The relatively recently sampled number of speech samples are extracted from the speech signal. The method further includes resuming transmission of the speech signal at predetermined time intervals. If desired, the change in the frequency spectrum of the speech signal is determined by comparing a predetermined threshold, and the change in the energy level of the speech signal is determined by comparing a predetermined threshold. 
     Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system diagram illustrating one embodiment of a speech coding system built in accordance with the present invention. 
     FIG. 2 is a system diagram illustrating one embodiment of a speech signal processing system built in accordance with the present invention. 
     FIG. 3 is a system diagram illustrating one embodiment of a speech codec built in accordance with the present invention. 
     FIG. 4 is a system diagram illustrating another embodiment of a speech codec built in accordance with the present invention. 
     FIG. 5 is a system diagram illustrating another embodiment of a speech codec built in accordance with the present invention. 
     FIG. 6A is a system diagram illustrating another embodiment of a speech codec built in accordance with the present invention. 
     FIG. 6B is a system diagram illustrating another embodiment of a speech codec built in accordance with the present invention. 
     FIG. 7 is a functional block diagram illustrating on e embodiment of a speech signal transmission method that detects and transmits a frequency spectrum and an energy level of a speech signal in accordance with the present invention. 
     FIG. 8 is a functional block diagram illustrating one embodiment of a n energy level and a frequency spectrum monitoring method performed within a discontinued transmission (DTX) method in accordance with the present invention. 
     FIG. 9 is a functional block diagram illustrating a speech coding method that determines whether to perform discontinued transmission (DTX) in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a system that provides and maintains a high perceptual quality of background noise contained within a speech signal. This maintenance of the high perceptual quality of the background noise is especially desirable within speech coding systems that perform discontinued transmission (DTX) and its associated comfort noise generation (CNG) contained therein. In addition, the invention offers a solution that is completely fully backward compatible with existing speech coding systems. This is especially desirable within pulse code modulation (PCM) speech coding systems that have inherently limited design constraints as described above in the related art. 
     FIG. 1 is a system diagram illustrating one embodiment of a speech coding system  100  built in accordance with the present invention. The speech coding system  100  contains, among other things, a speech codec  110 . The speech codec  110  receives an input speech signal  120  and generates an output speech signal  130 . The speech codec  110  itself contains, among other things, a background noise detection circuitry  112  and a speech signal analysis circuitry  114 . The background noise detection circuitry  112  itself contains, among other things, a frequency spectrum change detection circuitry  112   a  and an energy level change detection circuitry  112   b . The speech signal analysis circuitry  114  itself contains, among other things, a frequency spectrum change calculation circuitry  114   a  and an energy level change calculation circuitry  114   b.    
     In certain embodiments of the invention, the speech signal analysis circuitry  114  employs the frequency spectrum change calculation circuitry  114   a  and the energy level change calculation circuitry  114   b  to extract and calculate a frequency spectrum and an energy level from the input speech signal  120 . In addition, the background noise detection circuitry  112  employs the frequency spectrum change detection circuitry  112   a  and the energy level change detection circuitry  112   b  to detect any change in the frequency spectrum and the energy level from the input speech signal  120 . That is to say, the background noise detection circuitry  112  monitors for any changes of a background noise within the input speech signal  120 . In the event of any change in the frequency spectrum and the energy level within the input speech signal  120 , the speech codec  110  is operable to modify the method of transformation performed to convert the input speech signal  120  into the output speech signal  130 . If desired, the speech codec  110  is operable to perform discontinued transmission (DTX), and the speech codec  110  employs the background noise detection circuitry  112 , and the frequency spectrum change detection circuitry  112   a  and the energy level change detection circuitry  112   b  contained therein, to monitor any changes in the frequency spectrum and the energy level of the input signal  120 . In addition, if there is a sufficiently appreciable change in one or both of the frequency spectrum or the energy level of the input signal  110 , the speech codec  110  modifies the method of transformation performed to convert the input speech signal  120  into the output speech signal  130 . 
     FIG. 2 is a system diagram illustrating one embodiment of a speech signal processing system  200  built in accordance with the present invention. The speech signal processor  210  receives an unprocessed speech signal  220  and produces a processed speech signal  230 . 
     In certain embodiments of the invention, the speech signal processor  210  is processing circuitry that performs the loading of the unprocessed speech signal  220  into a memory from which selected portions of the unprocessed speech signal  220  are processed in various manners including a sequential manner. The processing circuitry possesses insufficient processing capability to handle the entirety of the unprocessed speech signal  220  at a single, given time. The processing circuitry may employ any method known in the art that transfers data from a memory for processing and returns the processed speech signal  230  to the memory. In other embodiments of the invention, the speech signal processor  210  is a system that converts a speech signal into encoded speech data. The encoded speech data is then used to generate a reproduced speech signal that is substantially perceptually indistinguishable from the speech signal using speech reproduction circuitry. In other embodiments of the invention, the speech signal processor  210  is a system that converts encoded speech data, represented as the unprocessed speech signal  220 , into decoded and reproduced speech data, represented as the processed speech signal  230 . In other embodiments of the invention, the speech signal processor  210  converts encoded speech data that is already in a form suitable for generating a reproduced speech signal that is substantially perceptually indistinguishable from the speech signal, yet additional processing is performed to improve the perceptual quality of the encoded speech data for reproduction. 
     The speech signal processing system  200  is, in some embodiments, the speech coding system  100  as described in the FIG.  1 . The speech signal processor  210  operates to convert the unprocessed speech signal  220  into the processed speech signal  230 . The conversion performed by the speech signal processor  210  is viewed, in various embodiments of the invention, as taking place at any interface wherein data must be converted from one form to another, i.e. from speech data to coded speech data, from coded data to a reproduced speech signal, etc. The speech coding performed in accordance with the present invention is performed, in various embodiments of the invention, within the speech signal processor  210 . From certain perspectives, the conversion of the unprocessed speech signal  220  into the processed speech signal  230  is the extraction of the linear prediction coefficients (LPCs) and the combination of the linear prediction coefficients (LPCs), as described above in the various embodiments of the invention. 
     FIG. 3 is a system diagram illustrating one embodiment of a speech codec  300  built in accordance with the present invention. The speech codec  300  employs an encoder circuitry  340  and a decoder circuitry  350  to transform a speech signal  320  into a reproduced speech signal  330 . The encoder circuitry  340  transforms the speech signal  320  into a form suitable for transmission via a communication link  310 . If desired, the transmission protocol employed across the communication link  310  is operable with conventional transmission protocols. Any number of additional transmission protocols are operable using the communication link  310 . The speech signal  320  itself contains, among other things, a background noise  322 . The reproduced speech signal  330  itself contains, among other things, a reproduced background noise  332  that is of a high perceptual quality. The perceptual quality of the reproduced background noise  332  contained within the reproduced speech signal  330  is substantially indistinguishable from the background noise  322  contained within the speech signal  320 . 
     In certain embodiments of the invention, information corresponding to a frequency spectrum and an energy level of the speech signal  320  are used to perform the speech coding of the speech signal  320  in accordance with the present invention. When the speech codec  300  begins to operate within a discontinued transmission (DTX) mode, a predetermined number of frames of the speech signal  320  are transmitted from the encoder circuitry  340  to the decoder circuitry  350  via the communication link  310 . If desired, one single frame of the speech signal  320  is transmitted from the encoder circuitry  340  to the decoder circuitry  350  via the communication link  310  after the discontinued transmission (DTX) mode of operation has been invoked. Using the predetermined number of frames of the speech signal  320 , or the one single frame of the speech signal  320  in other embodiments of the invention, the reproduced speech signal  330  is re-synthesized to provide the perceptually comforting comfort noise generation (CNG) to a user of the speech codec  300 . 
     In addition, speech codec  300  is operable to detect any change in the frequency spectrum and the energy level of the speech signal  320  and to modify the speech coding performed therein. Upon the detection of any change in the frequency spectrum and the energy level of the speech signal  320  being beyond a predetermined threshold for each of the parameters of the frequency spectrum and the energy level, the speech codec  300  re-initiates the discontinued transmission (DTX) mode of operation using the new frequency spectrum and the energy level of the speech signal  320 . This updating or refreshing of the frequency spectrum and the energy level of the speech signal  320  upon the ensure a high perceptual quality of the reproduced speech signal  330 , namely, a high perceptual quality of the reproduced background noise  332  contained within the reproduced speech signal  330 . 
     FIG. 4 is a system diagram illustrating another embodiment of a speech codec  400  built in accordance with the present invention. The speech codec  400  employs an encoder circuitry  440  and a decoder circuitry  450  to transform a speech signal  420  into a reproduced speech signal  430 . The encoder circuitry  440  transforms the speech signal  420  into a form suitable for transmission via a communication link  410 . If desired, the transmission protocol employed across the communication link  410  is operable with conventional transmission protocols. Any number of additional transmission protocols are operable using the communication link  410 . The speech signal  420  itself contains, among other things, a background noise  422 . The reproduced speech signal  430  itself contains, among other things, a reproduced background noise  432  that is of a high perceptual quality. The perceptual quality of the reproduced background noise  432  contained within the reproduced speech signal  430  is substantially indistinguishable from the background noise  422  contained within the speech signal  420 . 
     In certain embodiments of the invention, information corresponding to a frequency spectrum and an energy level of the speech signal  420  are used to perform the speech coding of the speech signal  420  in accordance with the present invention. When the speech codec  400  begins to operate within a discontinued transmission (DTX) mode, a predetermined number of frames of the speech signal  420  are transmitted from the encoder circuitry  440  to the decoder circuitry  450  via the communication link  410 . If desired, one single frame of the speech signal  420  is transmitted from the encoder circuitry  440  to the decoder circuitry  450  via the communication link  410  after the discontinued transmission (DTX) mode of operation has been invoked. Using the predetermined number of frames of the speech signal  420 , or the one single frame of the speech signal  420  in other embodiments of the invention, the reproduced speech signal  430  is re-synthesized to provide the perceptually comforting comfort noise generation (CNG) to a user of the speech codec  400 . 
     In addition, speech codec  400  is operable to detect any change in the frequency spectrum and the energy level of the speech signal  420  and to modify the speech coding performed therein. Upon the detection of any change in the frequency spectrum and the energy level of the speech signal  420  being beyond a predetermined threshold for each of the parameters of the frequency spectrum and the energy level, the speech codec  400  re-initiates the discontinued transmission (DTX) mode of operation using the new frequency spectrum and the energy level of the speech signal  420 . From some perspectives, transmission is resumed between the encoder circuitry  440  and the decoder circuitry  450  via the communication link  410 , whenever there is an appreciable change in either one of the frequency spectrum or the energy level of the speech signal  420 . If desired, a decision to resume transmission is performed when there is an appreciable change in both the frequency spectrum and the energy level of the speech signal  420 . Variations of the invention, including performing calculating weighted averages of the frequency spectrum and the energy level of the speech signal  420 , are performed without departing from the scope and spirit of the invention. This updating or refreshing of the frequency spectrum and the energy level of the speech signal  420  upon the ensure a high perceptual quality of the reproduced speech signal  430 , namely, a high perceptual quality of the reproduced background noise  432  contained within the reproduced speech signal  430 . 
     The encoder circuitry  440  itself contains, among other things, a discontinued transmission (DTX) circuitry  442 . The discontinued transmission (DTX) circuitry  442  itself contains, among other things, a voice activity detection (VAD) circuitry  444 , a background noise detection circuitry  448  that operates cooperatively with a transmission resuming circuitry  446 . The background noise detection circuitry  448  itself contains, among other things, a frequency spectrum change detection circuitry  448   a  and an energy level change detection circuitry  448   b.    
     The voice activity detection (VAD) circuitry  444  monitors the speech signal  420  to determine when to perform discontinued transmission (DTX). Once discontinued transmission (DTX) is invoked, the transmission resuming circuitry  446  is used to determine at which point during the discontinued transmission (DTX) mode of operation that transmission between the encoder circuitry  440  and the decoder circuitry  450 , via the communication link  410 , should resume to maintain a high perceptual quality of the background noise  422 . That is to say, during comfort noise generation (CNG) and other periods of speech coding that is performed when there is no active voiced speech in the speech signal  420 , one such example being the discontinued transmission (DTX) that is invoked by the discontinued transmission (DTX) circuitry  442 , the speech codec  400  is operable to maintain a high perceptual quality of even the background noise  422  within the speech signal  420 . 
     The decoder circuitry  450  itself contains, among other things, a decoder speech sample re-synthesis circuitry  452 . The decoder speech sample re-synthesis circuitry  452  itself contains, among other things, a background noise reproduction circuitry  458 . The background noise reproduction circuitry  458  itself contains, among other things, a frequency spectrum derivation circuitry  458   a  and an energy level derivation circuitry  458   b . The background noise reproduction circuitry  458  employs a number of recently received speech samples  452  to perform re-synthesis of the speech signal  420  within the reproduced speech signal  430  in a manner that is substantially imperceptible from original speech signal  420 . Specifically, the reproduced background noise  432  contained within the reproduced speech signal  430  is substantially imperceptible from the background noise  422  within the speech signal  420 . During discontinued transmission (DTX), as determined by the discontinued transmission (DTX) circuitry  442  within the encoder circuitry  440 , the speech codec  400  employs the decoder speech sample re-synthesis circuitry  452  to provide for comfort noise generation (CNG), in that, the reproduced speech signal  430  is generated with the reproduced background noise  432  contained therein. The decoder speech sample re-synthesis circuitry  452  retains a number of recently received speech samples  454 . The recently received speech samples  454  consists of, at least, a frequency spectrum  454   a  and an energy level  454   b  corresponding to the recently received speech samples  454 . Any number constitutes the total number of the recently received speech samples  454 . For example, in certain embodiments of the invention, the recently received speech samples  454  is a single frame of the speech signal  420 . In other embodiments of the invention, the recently received speech samples  454  is a predetermined number of frames of the speech signal  420  or a predetermined number of sub-frames of the speech signal  420 . Any number of speech samples is used to constitute the recently received speech samples  454  without departing from the scope and spirit of the invention. 
     At the decoder circuitry  450 , the frequency spectrum and the energy level of the speech signal  420  are derived using the background noise reproduction circuitry  458  and the frequency spectrum derivation circuitry  458   a  and the energy level derivation circuitry  458   b  contained therein. Specifically, when transmission is discontinued, as in the discontinued transmission (DTX) mode of operation, as determined by the discontinued transmission (DTX) circuitry  442  of the encoder circuitry  440 , the decoder circuitry  450  simply re-synthesizes speech samples that are substantially perceptually indistinguishable from the speech signal  420  and the background noise contained therein, using the recently received speech samples  454  and the frequency spectrum  454   a  and the energy level  454   b  contained therein. That is to say, the background noise reproduction circuitry  458  uses the spectrum and energy information derived from the recently received speech samples  454  to re-synthesize the speech signal  420  and the background noise  422  contained therein during the discontinued transmission (DTX) mode of operation. 
     This embodiment of the invention provides for full backward compatibility with conventional speech coding systems. In addition, it allows a manufacturer of the speech codec  400  to decide of what kind of frequency spectrum and energy level information it wants to derive from the recently received speech samples  454  to re-synthesize the speech signal  420 . In addition, how the comfort noise generation (CNG) is performed with the most economical approach is also left in the hands of the manufacturer of the speech codec  400 . At the encoder circuitry  440 , the use of the voice activity detection (VAD) circuitry  444  of a high quality and a high quality discontinued transmission (DTX) scheme as performed by the discontinued transmission (DTX) circuitry  442  ensure a balanced approach of two of the primary competing requirements of the speech codec  400  in maintaining a high perceptual quality of coding the background noise  422  and also maintaining desirable bit-savings by discontinuing transmission within the discontinued transmission (DTX) mode of operation. 
     The present invention provides for a perceptual quality during the discontinued transmission (DTX) mode of operation that is substantially comparable to the ITU-Recommendation G.729 Annex B comfort noise generation (CNG) standard because it employs the same information that is used for comfort noise generation (CNG). Those having skill in the art of speech coding systems are typically in agreement that the comfort noise generation (CNG) as provided by the ITU-Recommendation G.729 Annex B is perfectly meeting the perceptual quality expectation among users of speech coding systems for typical applications including those intended to be performed by the speech coded  400  as described within the invention. 
     FIG. 5 is a system diagram illustrating another embodiment of a speech codec  500  built in accordance with the present invention. The speech codec  500  employs an encoder circuitry  540  and a decoder circuitry  550  to transform a speech signal  520  into a reproduced speech signal  530 . The encoder circuitry  540  transforms the speech signal  520  into a form suitable for transmission via a communication link  510 . If desired, the transmission protocol employed across the communication link  510  is operable with conventional transmission protocols. Any number of additional transmission protocols are operable using the communication link  510 . The speech signal  520  itself contains, among other things, a background noise  522 . The reproduced speech signal  530  itself contains, among other things, a reproduced background noise  532  that is of a high perceptual quality. The perceptual quality of the reproduced background noise  532  contained within the reproduced speech signal  530  is substantially indistinguishable from the background noise  522  contained within the speech signal  520 . 
     In certain embodiments of the invention, information corresponding to a frequency spectrum and an energy level of the speech signal  520  are used to perform the speech coding of the speech signal  520  in accordance with the present invention. When the speech codec  500  begins to operate within a discontinued transmission (DTX) mode, a predetermined number of frames of the speech signal  520  are transmitted from the encoder circuitry  540  to the decoder circuitry  550  via the communication link  510 . If desired, one single frame of the speech signal  520  is transmitted from the encoder circuitry  540  to the decoder circuitry  550  via the communication link  510  after the discontinued transmission (DTX) mode of operation has been invoked. Using the predetermined number of frames of the speech signal  520 , or the one single frame of the speech signal  520  in other embodiments of the invention, the reproduced speech signal  530  is re-synthesized to provide the perceptually comforting comfort noise generation (CNG) to a user of the speech codec  500 . 
     In addition, speech codec  500  is operable to detect any change in the frequency spectrum and the energy level of the speech signal  520  and to modify the speech coding performed therein. Upon the detection of any change in the frequency spectrum and the energy level of the speech signal  520  being beyond a predetermined threshold for each of the parameters of the frequency spectrum and the energy level, the speech codec  500  re-initiates the discontinued transmission (DTX) mode of operation using the new frequency spectrum and the energy level of the speech signal  520 . From some perspectives, transmission is resumed between the encoder circuitry  540  and the decoder circuitry  550  via the communication link  510 , whenever there is an appreciable change in either one of the frequency spectrum or the energy level of the speech signal  520 . If desired, a decision to resume transmission is performed when there is an appreciable change in both the frequency spectrum and the energy level of the speech signal  520 . Variations of the invention, including performing calculating weighted averages of the frequency spectrum and the energy level of the speech signal  520 , are performed without departing from the scope and spirit of the invention. This updating or refreshing of the frequency spectrum and the energy level of the speech signal  520  upon the ensure a high perceptual quality of the reproduced speech signal  530 , namely, a high perceptual quality of the reproduced background noise  532  contained within the reproduced speech signal  530 . 
     The encoder circuitry  540  itself contains, among other things, a discontinued transmission (DTX) circuitry  542 . The discontinued transmission (DTX) circuitry  542  itself contains, among other things, an intelligent discontinued transmission (DTX) circuitry  546  that operates cooperatively with a background noise detection circuitry  548 . The background noise detection circuitry  548  itself contains, among other things, a frequency spectrum change detection circuitry  548   a  and an energy level change detection circuitry  548   b . During the discontinued transmission (DTX) mode of operation, the intelligent discontinued transmission (DTX) circuitry  546  is operable to detect an appreciable change in either the frequency spectrum or the energy level of the speech signal  520 , and the intelligent discontinued transmission (DTX) circuitry  546  resumes transmission from the encoder circuitry  540  to the decoder circuitry  550  via the communication link  510  at this time. In alternative embodiments of the invention, a systematic discontinued transmission (DTX) circuitry  544  simple transmits information corresponding to the frequency spectrum and the energy level of the speech signal  520  at predetermined intervals of time. In these embodiments of the invention, to guarantee a very high perceptual quality of speech coding of the background noise  522  during the discontinued transmission (DTX) mode of operation, the predetermined intervals of time are relatively short thereby providing ample information of the background noise  522  very frequently. 
     Alternatively, for applications wherein the speech codec  500  is constrained by a substantially limited bandwidth and low bit budget, the predetermined intervals of time are relatively long thereby providing perhaps a reduced perceptual quality of the background noise  522 , yet other design constraints are met within this particular embodiment of the invention. If desired, both the systematic discontinued transmission (DTX) circuitry  544  and the intelligent discontinued transmission (DTX) circuitry  546  are contained within a single embodiment of the invention, and depending on the operating characteristics of the communication link  510  at any given time, the speech codec  500  is operable to switch between using the systematic discontinued transmission (DTX) circuitry  544  and the intelligent discontinued transmission (DTX) circuitry  546 . For example, when a relatively large amount of bandwidth is available within the communication link  510  of the speech codec  500 , the systematic discontinued transmission (DTX) circuitry  544  could be employed, thereby ensuring a high perceptual quality of the background noise  522 . However, when additional considerations are met, such as a relatively constrained bandwidth of the communication link  510 , the intelligent discontinued transmission (DTX) circuitry  546  thereby providing a substantial bit savings. 
     FIG. 6A is a system diagram illustrating another embodiment of a speech codec  600  built in accordance with the present invention. The speech codec  600  employs a conventional encoder circuitry  640  and a decoder circuitry  650  to transform a speech signal  620  into a reproduced speech signal  630 . The encoder circuitry  640  transforms the speech signal  620  into a form suitable for transmission via a communication link  610 . If desired, the transmission protocol employed across the communication link  610  is operable with conventional transmission protocols. Any number of additional transmission protocols are operable using the communication link  610 . The speech signal  620  itself contains, among other things, a background noise. The reproduced speech signal  630  itself contains, among other things, a reproduced background noise that is of a high perceptual quality. The perceptual quality of the reproduced background noise contained within the reproduced speech signal  630  is substantially indistinguishable from any background noise contained within the speech signal  620 . 
     The conventional encoder circuitry  640  is an encoder circuitry of s speech codec that is operable using a variety of conventional transmission protocols, including but not limited to the ITU-Recommendation transmission protocols with all of its associated Annexes. The decoder circuitry  650  is operable for full backward compatibility with the conventional encoder circuitry  640  and is operable to perform conventional transmission protocols over the communication link  610 . One portion of the functionality proffered by the speech codec  600  is the ability for the decoder circuitry  650  to integrate completely with existing speech codecs that do not offer certain aspects of the invention as described in other embodiments of the invention. For example, other embodiments of the invention provide for maintaining a high perceptual quality of any background noise that is found in the speech signal  620 . However, as described above in various embodiments of the invention and in various embodiments of the conventional art, those conventionally proposed methods of performing speech coding that maintains a high perceptual quality of the background noise that is found in the speech signal  620  are inherently incapable of integration into existing speech codecs and incapable of accommodating conventional transmission protocols contained therein. 
     The speech codec  600  is illustrative of one such speech codec having the decoder circuitry  650  that itself is operable to provide the increased functionality of maintains a high perceptual quality of any background noise that is found in the speech signal  620 , yet the decoder circuitry  650  is operable for integration into speech codecs having portions of circuitry, namely the conventional encoder circuitry  640 , that is incapable to maintain a high perceptual quality of any background noise. The speech codec  600  provides a speech codec that is capable of fall integration into both speech codecs that are operable to provide and maintain a high perceptual quality of any background noise found in the speech signal  620  and is also capable of full integration into speech codecs that contain all or part of their circuitry that is only operable to use conventional methods of discontinued transmission (DTX), silence insertion description (SID), and other methods of speech coding that provide for advanced and improved perceptual quality to an end user of the speech codec  600  or other speech codecs included within the scope and spirit of the invention. 
     FIG. 6B is a system diagram illustrating another embodiment of a speech codec  605  built in accordance with the present invention. The speech codec  605  employs an encoder circuitry  645  and a conventional decoder circuitry  655  to transform a speech signal  625  into a reproduced speech signal  635 . The encoder circuitry  645  transforms the speech signal  625  into a form suitable for transmission via a communication link  615 . If desired, the transmission protocol employed across the communication link  615  is operable with conventional transmission protocols. Any number of additional transmission protocols are operable using the communication link  615 . The speech signal  625  itself contains, among other things, a background noise. The reproduced speech signal  635  itself contains, among other things, a reproduced background noise that is of a high perceptual quality. The perceptual quality of the reproduced background noise contained within the reproduced speech signal  635  is substantially indistinguishable from any background noise contained within the speech signal  625 . 
     The conventional decoder circuitry  655  is an decoder circuitry of s speech codec that is operable using a variety of conventional transmission protocols, including but not limited to the ITU-Recommendation transmission protocols with all of its associated Annexes. The encoder circuitry  645  is operable for full backward compatibility with the conventional decoder circuitry  655  and is operable to perform conventional transmission protocols over the communication link  615 . One portion of the functionality proffered by the speech codec  605  is the ability for the decoder circuitry  655  to integrate completely with existing speech codecs that do not offer certain aspects of the invention as described in other embodiments of the invention. For example, other embodiments of the invention provide for maintaining a high perceptual quality of any background noise that is found in the speech signal  625 . However, as described above in various embodiments of the invention and in various embodiments of the conventional art, those conventionally proposed methods of performing speech coding that maintains a high perceptual quality of the background noise that is found in the speech signal  625  are inherently incapable of integration into existing speech codecs and incapable of accommodating conventional transmission protocols contained therein. 
     The speech codec  605  is illustrative of one such speech codec having the encoder circuitry  645  that itself is operable to provide the increased functionality of maintains a high perceptual quality of any background noise that is found in the speech signal  625 , yet the encoder circuitry  645  is operable for integration into speech codecs having portions of circuitry, namely the conventional decoder circuitry  655 , that is incapable to maintain a high perceptual quality of any background noise. The speech codec  605  provides a speech codec that is capable of full integration into both speech codecs that are operable to provide and maintain a high perceptual quality of any background noise found in the speech signal  625  and is also capable of full integration into speech codecs that contain all or part of their circuitry that is only operable to use conventional methods of discontinued transmission (DTX), silence insertion description (SID), and other methods of speech coding that provide for advanced and improved perceptual quality to an end user of the speech codec  605  or other speech codecs included within the scope and spirit of the invention. 
     FIG. 7 is a functional block diagram illustrating one embodiment of a speech signal transmission method  700  that detects and transmits a frequency spectrum and an energy level of a speech signal in accordance with the present invention. In a block  710 , a frequency spectrum of a speech signal is detected. Subsequently, in a block  720 , an energy level of the speech signal is detected. Finally, in a block  730 , the frequency spectrum and the energy level that are detected in the blocks  710  and  720 , respectively, are transmitted. In certain embodiments of the invention, the transmission that is performed in the block  730  is via any one of the communication links described above in any of the various embodiments of the invention. For example, the frequency spectrum and the energy level are each detected of the speech signal in an encoder circuitry (within the blocks  710  and  720 , respectively) and transmitted via a communication link to a decoder circuitry (within the block  730 ). Any variations of the detection of the frequency spectrum and the energy level of a speech signal are performed in other embodiments of the invention wherein the two parameters of the frequency spectrum and the energy level are detected and transmitted. 
     In certain embodiments of the invention, the detection of the frequency spectrum and the energy level in the blocks  710  and  720  is performed to ensure a high perceptual quality of any background noise contained within the speech signal. For example, by detecting the frequency spectrum and the energy level of the is in the blocks  710  and  720 , and by transmitting that information in the block  730 , any reproduction of the speech signal is operable to maintain the high perceptual quality of any background noise contained within the speech signal. This assurance of a high perceptual quality is especially important within various speech coding modes of operation including discontinued transmission (DTX) wherein comfort noise generation (CNG) is performed to provide to a user the perception of background noise being encoded, transmitted, and decoded and finally reproduced. 
     FIG. 8 is a functional block diagram illustrating one embodiment of an energy level and a frequency spectrum monitoring method  800  performed within a discontinued transmission (DTX) method in accordance with the present invention. In a block  810 , a frequency spectrum of a speech signal is detected. Subsequently, in a block  820 , an energy level of the speech signal is detected. Then, in a block  822   a , any change (Δ) of the frequency spectrum of the speech signal that is detected in the block  810  is detected. Similarly, in a block  822   b , any change (Δ) of the energy level of the speech signal that is detected in the block  820  is detected. Subsequently, in the event of the detection of any change (Δ) of the frequency spectrum of the speech signal as performed in the block  822   a , a decision is made in the decision block  824   a  whether there is any change (Δ) of the frequency spectrum of the speech signal. Similarly, in the event of the detection of any change (Δ) of the energy level of the speech signal as performed in the block  822   b , a decision is made in the decision block  824   b  whether there is any change (Δ) of the energy level of the speech signal. 
     If desired in certain embodiments of the invention, the change (Δ) of the frequency spectrum of the speech signal is compared against a predetermined threshold, so that a substantially minor change (Δ) of the frequency spectrum of the speech signal is not categorized as an “actual” change (Δ) of the frequency spectrum of the speech signal. Alternatively, intelligent schemes that are used to determine when to treat the change (Δ) of the frequency spectrum of the speech signal as an “actual” change (Δ) of the frequency spectrum of the speech signal. That is to say, a user that performs the energy level and the frequency spectrum monitoring method  800  is capable of setting various thresholds below which any change (Δ) of the frequency spectrum of the speech signal will be deemed to be simply noise. The decision performed in the decision block  824   a  is operable in the fashion described herein using thresholds and other intelligently comparative methods of comparison. 
     If desired in certain embodiments of the invention, the change (Δ) of the energy level of the speech signal is compared against a predetermined threshold, so that a substantially minor change (Δ) of the energy level of the speech signal is not categorized as an “actual” change (Δ) of the energy level of the speech signal. Alternatively, intelligent schemes that are used to determine when to treat the change (Δ) of the energy level of the speech signal as an “actual” change (Δ) of the energy level of the speech signal. That is to say, a user that performs the energy level and the frequency spectrum monitoring method  800  is capable of setting various thresholds below which any change (Δ) of the energy level of the speech signal will be deemed to be simply noise. The decision performed in the decision block  824   b  is operable in the fashion described herein using thresholds and other intelligently comparative methods of comparison. 
     In the event that there is a detected change (Δ) of the frequency spectrum of the speech signal in the decision block  824   a  or a detected change (Δ) of the energy level of the speech signal in the decision block  824   b , transmission is resumed in a block  826 . In embodiments of the invention wherein the energy level and the frequency spectrum monitoring method  800  is performed within a speech codec, the transmission that is resumed in the block  826  is that via a communication link between an encoder circuitry and a decoder circuitry. Finally, in a block  830 , the frequency spectrum and the energy level that are detected in the blocks  810  and  820 , respectively, are transmitted. 
     In alternative embodiments of the invention, after there is a detected change (Δ) of the frequency spectrum of the speech signal in the decision block  824   a , then transmission is resumed in a block  826   a . Afterwards, in a block  830   a , the frequency spectrum that is detected in the block  810  is transmitted. In this embodiment of the invention, the frequency spectrum is transmitted alone without the energy level being transmitted. In even other embodiments of the invention, after there is a detected change (Δ) of the energy level of the speech signal in the decision block  824   b , then transmission is resumed in a block  826   b . Afterwards, in a block  830   b , the energy level that is detected in the block  820  is transmitted. In this embodiment of the invention, the energy level is transmitted alone without the frequency spectrum being transmitted. 
     FIG. 9 is a functional block diagram illustrating a speech coding method  900  that determines whether to perform discontinued transmission (DTX) in accordance with the present invention. In a block  910 , it is determined whether to use a discontinued transmission (DTX) mode of operation. In a decision block  915 , it is then determined whether the discontinued transmission (DTX) mode of operation is selected in the block  910 . If the discontinued transmission (DTX) mode of operation is not selected, then the speech coding method  900  terminates. Alternatively, if the discontinued transmission (DTX) mode of operation is not selected, then transmission is performed for a predetermined number of additional frames of a speech signal in a block  917 . In alternative embodiments of the invention, transmission is continued for one additional frame of the speech signal. Any number of additional frames is used without departing from the scope and spirit of the invention. Subsequently, in a block  920 , speech samples are re-synthesized using most recent speech signal information. In certain embodiments of the invention, this speech signal information is made up of the frequency spectrum and energy level of the speech signal. 
     Then, in a block  922   a , any change (Δ) of the frequency spectrum of the speech signal is detected. Similarly, in a block  922   b , any change (Δ) of the energy level of the speech signal is detected. Subsequently, in the event of the detection of any change (Δ) of the frequency spectrum of the speech signal as performed in the block  922   a , a decision is made in the decision block  924   a  whether there is any change (Δ) of the frequency spectrum of the speech signal. Similarly, in the event of the detection of any change (Δ) of the energy level of the speech signal as performed in the block  922   b , a decision is made in the decision block  924   b  whether there is any change (Δ) of the energy level of the speech signal. If there is no change in either the frequency spectrum or energy level, as decided in the decision blocks  922   a  and  922   b , then the speech coding method  900  returns to the blocks  922   a  and  922   b , respectively. Similar to and as described above, with respect to the comparison of the change of either frequency spectrum or energy level, the decision performed in the decision blocks  922   a  and  922   b  is operable against predetermined thresholds. 
     However, is any change is detected in the frequency spectrum or energy level, as decided in the decision blocks  922   a  and  922   b , then the speech coding method  900  returns to the block  917  to transmit the predetermined number of additional frames of the speech signal. This will ensure maintenance of a high perceptual quality of background noise contained in the speech signal during the discontinued transmission (DTX) mode of operation. That is to say, the speech coding method  900  is operable to accommodate appreciable changes in either the frequency spectrum or the energy level of the background noise of the speech signal. 
     In view of the above detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the present invention.