Abstract: In a voice processing system employing the telephone communications network, any echo of an outgoing signal is substantially eliminated from the incoming signal by appropriately combining an appropriate version of the outgoing signal with the incoming signal so that there is destructive interference with any echo of the outgoing signal. To determine the appropriate version of the outgoing signal to be combined with the incoming signal, a brief training signal is applied to the telephone transmission line. The echo of this signal returned by the transmission line is stored and convolved with the time-inverse of the training signal to produce a function which approximates the impulse response of the transmission line. This function is thereafter used to produce the version of the outgoing signal which is combined with the incoming signal for echo cancellation.

Abstract: Digital samples of a voice signal are greatly compressed by filtering the samples to separate the information contained in them into several different frequency bands. In each of a succession of time intervals, the dominant filter output value is identified and converted to floating point form including an exponent and a generally truncated mantissa. All other filter output values for that time interval are also converted to floating point form having the same exponent. The mantissas are then further compressed by grouping values associated with each filter and again converting the mantissas in each group to floating point form having a common local exponent and submantissas. The Walsh-Haddamard transfer is also employed.

Abstract: A voice message system having a plurality of user voice mailboxes is disclosed. The voice message system utilizes a method in which a message is encrypted using a unique encrypting key corresponding to a designated user. The encrypted message is then stored in one location while the encrypting key is stored in another location. The encrypted message is retrieved by the designated user by utilizing a decrypting key which corresponds to the stored encrypting key. The decrypted message is then played by the designated user.

Abstract: A direct inward dial integration device is connected to the trunk side of a PBX in a business telephone system. The present invention permits a voice message system (VMS) to answer forwarded calls with a personal greeting of a called party. When a direct inward dial call is made, the identity of the extension (i.e., the extension number) being called is transmitted to the PBX by the telephone system. The integration device detects and stores the extension identity. If an incoming call is forwarded to the VMS, the VMS generates a query sigal, which causes the integration device to automatically transmit the stored extension number to the voice message system. Thus the voice message system can identify the called party. The VMS responds by answering the call with a personal greeting of the called party and inviting the outside caller to leave a recorded message.

Abstract: A telephone line quality testing system detects line echoes in the telephone connection between two subsystems in a message transmission system. The test for line echoes is performed while the two subsystems exchange identification data by transmitting DTMF signals in a predefined sequence. Each subsystem transmits a marker at the beginning of each DTMF transmission. This marker is constructed so that it can be distinguished, with absolute certainty, from any possible echo of the previous DTMF transmission by the other subsystem. In general, the marker includes at least one DTMF signal selected from the set of DTMF signals not included in the last X DTMF signals sent by the other subsystem. Each subsystem also generates an "Expected marker" that should precede the next DTMF transmission by the other subsystem. When receiving a DTMF transmission, each subsystem compares the initial DTMF signals received with the expected marker.