Patent Publication Number: US-7224794-B1

Title: Transmitting message playback concurrent with speakerphone operation

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to speakerphones including a voice messaging function. More particularly, it relates to the inclusion of a voice message playback signal together with a speakerphone signal in a telephone conversation. 
   2. Background of Related Art 
   Voice messaging systems such as telephone answering devices are well known. A typical telephone answering device allows a caller to record a voice message for a user who fails to answer an incoming telephone call. Initially, voice messaging systems recorded voice messages onto magnetic cassette tapes. However, more recent voice messaging systems record voice messages into digital memory (e.g., typically non-volatile memory such as Flash memory). 
   To retrieve a recorded voice message, a user typically activates a PLAY function of the telephone answering device, either locally or from a remote location over a telephone line. In a remote access mode, the conventional telephone answering device replaces handset access to the telephone line with a signal path from the played back voice messages to the telephone line. In either case, the playback of a voice message is conventionally heard only by the user, either locally or at the remote location. 
   Oftentimes it is desired to share a particular voice message with someone else. To do so, the conventional user must call and verbally paraphrase or repeat the voice message which they played back for themselves. It is possible to playback a voice message and hold the handset of a telephone toward the speaker of the telephone answering device, allowing an uncontrolled level of the played back voice message to be coupled into the telephone call between the user and the other person at the far end of a telephone call. Unfortunately, this typically requires the user to take the handset away from their own ear, preventing the user from participating in a conversation with the far end party while picking up some level of the played back message. 
   There is a need for an improved apparatus and technique for allowing a user of a telephone answering device to share a recorded voice message with another party. 
   SUMMARY OF THE INVENTION 
   In accordance with the principles of the present invention, a transmit path of a voice messaging system with speakerphone capability comprises a microphone signal, a gain module, a message playback signal relating to a pre-recorded voice message, and a summer in the transmit path. The message playback signal is combined with the microphone signal for transmission over a telephone line such that a far end user will simultaneously hear the microphone signal and the message playback signal. 
   A method of simultaneously transmitting a microphone signal and a played back pre-recorded voice signal to a far end party over a telephone line using a speakerphone in accordance with another aspect of the present invention comprises establishing a telephone call. A transmit function of a speakerphone generating a microphone signal is initiated. A voice message pre-recorded on the speakerphone generating a playback message signal is played back. The microphone signal is combined with the playback message signal, and the combined microphone signal and playback signal are transmitted to a far end party over a telephone line. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the drawings, in which: 
       FIG. 1  shows a block diagram of an exemplary full-duplex digital speakerphone allowing combination of a played back voice message with a speakerphone conversation, in accordance with the principles of the present invention. 
       FIG. 2  shows a block diagram of an exemplary full-duplex digital speakerphone allowing conversational record during speakerphone operation, in accordance with the principles of the present invention. 
       FIG. 3  shows an exemplary process flow of the digital speakerphone/telephone answering device shown in  FIG. 1  if no speakerphone conversation is present, the voice message will cause the speakerphone to transition to a receive Rx state, in accordance with the principles of the present invention. 
       FIG. 4  shows an exemplary process flow of the digital speakerphone/telephone answering device shown in  FIG. 1  during a normal receive Rx to transmit Tx break-in condition during normal speakerphone operation, in accordance with the principles of the present invention. 
       FIG. 5  shows an exemplary process flow of the digital speakerphone/telephone answering device shown in  FIG. 1  during a transmit Tx break-in during playback of the voice message, in accordance with the principles of the present invention. 
   

   DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
   The present invention allows simultaneous playback of a voice message recorded in a voice messaging system, e.g., in a telephone answering device (TAD), while using a speakerphone function of the telephone answering device. Simultaneous inclusion of both a speakerphone conversation and a played back voice message allows both parties to a telephone conversation to listen to the message at a controlled level and converse over the speakerphone at the same time. 
   Conventional echo canceling speakerphones incorporate Acoustic and Hybrid echo cancelers to eliminate or reduce Acoustic and Line echo respectively. In addition, both the transmit (Tx) and receive (Rx) paths (i.e., the microphone and speaker paths, respectively) have AGC (Automatic Gain Control) and Gain blocks which together perform a signal conditioning function for the conversation. In addition, two voice activity detectors, and Transmit and Receive switch guards or Ratio tests, are often used together with switching state logic to maintain stability and full duplex communication in a speakerphone conversation. 
   In accordance with the principles of the present invention, a message playback signal is incorporated into the conversation signal to allow the far end party to hear the voice message at the same time a local speakerphone user is hearing the voice message in a way which is controlled. The controlled combination of the conversation and message signals allows simultaneous conversation on the same telephone line as that used to transmit a voice message to the far end party. 
   In general, two telephone answering device functions can occur during speakerphone operation; conversation record, and playback of a previously recorded message or memo during speakerphone conversation. In accordance with the principles of the present invention, conversation record multiplexes the microphone and line-in signals for recording on an appropriate medium, e.g., on magnetic tape or into digital memory (e.g., Flash memory). 
   The present invention provides that a recorded message can be played back and heard by the far-end party as well as over the local speakerphone by the near-end party as if it were a normal receive signal. The present invention allows normal speakerphone operation to continue during this playback operation, allowing the far-end party and the near-end party to break-in over the message as desired and be heard by the other party. 
   It is preferred that both the message and conversation signals be at similar levels. However, the present invention relates equally to the suppression or amplification of either the conversation signal or the voice message playback signal. Moreover, it is preferred (but not absolutely necessary) that the message playback at the near end be subject to the same speakerphone digital volume control at the far end. 
     FIG. 1  shows a block diagram of an exemplary full-duplex digital speakerphone allowing combination of a played back voice message with a speakerphone conversation, in accordance with the principles of the present invention. 
   In particular, in  FIG. 1 , a telephone answering device with speakerphone capability  10  includes a message playback module  140  which generates an otherwise conventional message playback signal, and a speaker  152  and microphone  150  forming the basis of a speakerphone. 
   The microphone  150  provides a signal to a buffer/amplifier  154 , which then provides a signal to an analog-to-digital converter  102  (e.g., within a codec or similar device). The digitized microphone signal has audio echoes cancelled in a summer  192  using an acoustic echo canceller (AEC) in communication with the speaker path. This echo cancelled signal is fed to one side of a comparator  160 , with the other side of the comparator  160  being sourced from the speaker path. The output of the comparator  160  is provided to a suitable controller  170  through an appropriate gain module  161 . 
   A transmit voice activity detector  164  is in communication with the microphone path, and provides a controller  170  with a signal indicating the presence of transmit voice activity. 
   The digitized and acoustic echo cancelled microphone signal is amplified to a given desired level in an automatic gain control (AGC) amplifier  130 . 
   A fixed gain block  144  provides additional gain for input to a switched loss/echo suppression module  174 . The output of the switched loss/echo suppression module  174  is fed to a comparator  162 , which also receives an input from the speaker path before it is digitally amplified. The output of the comparator  162  is fed to the controller  170 . 
   The controller  170  may be any suitable processor, e.g., a digital signal processor (DSP), a microcontroller, or a microprocessor. 
   A hybrid echo canceller (HEC)  112  cancels the transmit signal from the received signal by adding an inverted representation of the transmitted signal to the received signal, appropriately delayed, in a digital summer  184 . 
   A digital-to-analog (D/A) converter  106  provides digital to analog conversion of the microphone path signal for injection onto a telephone line  122  through a hybrid  120 . 
   In a receive direction, a received analog signal from the hybrid  120  is input to an analog-to-digital (A/D) converter  104 . The output of the A/D converter  104  is added to an echo cancellation signal from the HEC  112 . 
   A receive voice activity detector  166  provides information regarding the presence of a received signal to the controller  170 . 
   The digitized and hybrid echo cancelled signal is amplified by an automatic gain control (AGC) module  132 . A digital gain module  146  provides further fixed gain as set, e.g., by a digital volume control. The output of the gain module  146  is input to a switched loss module  172 , which receives control information from the controller  170 . The output of the switched loss module  170  is converted to an analog signal in a D/A  108 , and output by the speaker  152  of the speakerphone  10 . 
   Furthermore, in accordance with the principles of the present invention, a voice message playback signal is injected into the microphone (i.e., transmit) path for the benefit of the far end party, preferably at a point before the HEC  112 . Also, or alternatively, the voice message playback signal may be injected into the receive path, i.e., into the local speaker path for the benefit of the near end party, preferably at a point after the HEC  112 . 
   In particular, the signal output from the message playback module  140  is subjected to a fixed gain module  142 , similar to that provided by the gain module  144  in the transmit path and to the gain module  146  in the receive path. This provides a desired level to the voice playback signal for injection at a controlled level into the receive and transmit paths of the speakerphone. 
   Preferably, a separate gain block  142  is applied to the played back voice message. Preferably, the gain level of the gain block  142  is at the same or similar level as that in the speakerphone transmit Tx path to keep the played back message and the conversation signals at the same or similar level. 
   The level-controlled message playback signal is digitally combined into the transmit path using the digital summer  180  in the transmit path before the D/A converter  106 , and is digitally combined into the receive path using the digital summer  182  after the A/D converter  104  in the receive path. 
   Message playback to the far end party is achieved by mixing the played back message signal from the message playback module  140  with the speakerphone transmit signal, preferably after the transmit signal conditioning blocks (e.g., the AGC  130  and gain module  144 ) and switched loss block  174 . 
   The HEC  112  cancels any hybrid echo of the message from appearing in the receive path. 
   The played back voice message is also to be heard over the local speaker  152  by the near-end party, preferably at the same level as the far-end party&#39;s conversation is heard. In the disclosed embodiment, this is accomplished by combining the played back voice message signal into the receive path before the AGC  132  and gain block  146 , but after the output from the HEC  112 . 
   In this way, the receive path AGC  132  maintains both the far-end conversation and the played back voice message at the same level for output by the speaker  152 . Moreover, the receive path digital volume control applies to both the level of the played back voice message as well as to the level of the conversation. 
   The Acoustic Echo Canceller (AEC)  110  is used to reduce the coupling between the microphone and the local speaker. The Hybrid Echo Canceller (HEC)  112  is used to reduce the hybrid coupling. 
   Both the transmit (Tx) and receive (Rx) paths have AGC (Automatic Gain Control)  130 ,  132  and gain blocks  144 ,  146  which together perform a signal conditioning function. The AGCs  130 ,  132  maintain a steady nominal output level with inputs over a much wider dynamic range. The gain blocks  144 ,  146  apply a fixed amplification or attenuation to the output of the AGCs  130 ,  132 , respectively. 
   In the receive path the gain block  146  is used to implement digital volume control. In the transmit path, the gain block  144  is used to maintain the required transmit level to the telephone line  122 . 
   Both the transmit Tx and receive Rx paths have a switched loss block  174 ,  172 , respectively, to maintain loop stability. In the transmit Tx path, the switched loss module  174  also includes echo suppression to provide residual echo control. 
   To overcome the switched loss in the receive path, the speakerphone  10  is preferably artificially forced to a receive state. For instance, this may be handled by forcing the line-ratio comparator  162  to indicate a receive condition during message playback. To those skilled in the art, the term “line-ratio” is also known as “receive switch guard”. 
   With the telephone answering system shown in  FIG. 1 , the far-end signal can be heard over the local speaker  152  mixed in with the playback of a voice message, all at a level adjusted by the digital volume control  146 . 
   A simultaneous presence of the played back message together with a far-end signal (determined by the receive voice activity detector  166 ) maintains the speakerphone  10  in a receive state. A sufficiently loud near end signal would cause the speakerphone  10  to break-in from a receive state to a transmit state. In the transmit state, the transmitted microphone signal is mixed with the signal from the message playback module  140  and heard at the far-end. 
   Accordingly, in order to transmit the message to the far-end, the voice message is combined at some point in the transmit Tx path. If the played back voice message signal is combined before the switched loss echo suppression module  174 , then the transmit Tx path should be kept active during the playback of the voice message. Otherwise, the voice message will not be heard at the far-end. However, because it is preferred to keep the transmit Tx path inactive and the receive Rx path active during playback of the voice message to allow the far end to hear the message playback, the voice message signal is preferably added in after the switched loss echo suppression module  174  as shown in  FIG. 1 . 
   The message playback will affect only the line-out input to the line-ratio (LR) comparator  162 . 
   It is also preferred that the voice message being played back be heard over the local speaker  152  by the near-end party, at the same level as the far-end conversation. In accordance with the principles of the present invention, this can be handled by combining the voice message signal in the transmit Tx path before the AGC  132  and gain block  146  in the receive Rx path, but after the output of the HEC  112 , as shown in  FIG. 1 . The AGC  132  maintains both the far-end conversation and the played back voice message at the same level. 
   The receive Rx digital volume control  146  preferably applies to both the played back voice message and to the conversation. 
   In  FIG. 1 , the message playback signal is presented to a fixed gain module  142 . However, this presumes that the recorded message (e.g., a conversational record message or a voice message received from a caller) was processed through an automatic gain control (AGC) module before it was recorded. 
   For instance,  FIG. 2  shows an exemplary system diagram showing signal flows allowing conversational record during speakerphone operation. In accordance with this aspect, a conversational record feature is used to record a voice message in suitable voice message memory for playback through the message playback module  140 . Of course, the principles of the present invention relate equally to an AGC module placed after the voice message is recorded, e.g., between the message playback module  140  and the fixed gain module  142 . 
     FIGS. 3 ,  4  and  5  show exemplary switching state diagrams of a digital speakerphone such as the one shown in  FIG. 1 , in accordance with the principles of the present invention. 
   In particular, in the state diagrams of  FIGS. 3 ,  4  and  5 , ME refers to the output of the Tx VAD (Transmit Voice Activity Detector)  164  shown in  FIG. 1 , LE to the output of the Rx VAD  166  shown in  FIG. 1 , LR to the decision of the Line-Ratio comparator test  162 , and AR to the decision of the Acoustic-ratio comparator test  160 . ME and LE refer to a speech activity decision as well as to an energy level when comparing ME and LE. 
   Referring back to  FIG. 1 , the playback of the voice message forces the output of the receive voice activity detector  166  to become active, e.g., LE=1, and forces the output of the line-ratio comparator  162  LR to be equal to R (i.e., in the receive Rx state). Also, the output of the transmit voice activity detector  164  becomes active, e.g., ME=1, and the output of the acoustic ratio comparator  160  becomes AR=R. 
     FIG. 3  shows that if no speakerphone conversation is present, the voice message will cause the speakerphone  10  to transition to a receive Rx state. 
   In accordance with the principles of the present invention, the far-end signal can be heard over the local speaker  152  mixed in with the played back voice message. A simultaneous presence of the far-end signal will maintain the receive activity condition active, e.g., LE=1 and LR=R, and will maintain the speakerphone  10  in a receive Rx state. 
     FIG. 4  shows an exemplary process flow of a normal receive Rx to transmit Tx break-in condition during normal speakerphone operation. 
     FIG. 5  shows an exemplary process flow of a transmit Tx break-in during playback of a voice message on a speakerphone as shown in  FIG. 1 . 
   As shown in  FIGS. 4 and 5 , a sufficiently loud near-end signal will cause the output of the acoustic ratio comparator  160  to indicate a transmit condition, e.g., AR=T and ME=1. If ME&gt;LE, then the speakerphone  10  switches to a transmit Tx condition. The microphone signal will then be mixed with the played voice message signal and heard at the far-end. 
   The concurrent capability of voice message playback combined with a conversation signal allows parties involved in a speakerphone conversation to jointly participate in listening to a message recorded on one party&#39;s telephone answering device, while at the same time continue their conversation using the speakerphone. 
   While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention.