There are various types of systems which automatically answer an incoming call and maintain a telephone line connection which are broadly defined as automatic telephone answering systems. These systems include, for example, message recording systems having remote access message playback, automatic dial-up alarm receiving equipment, automatic telephone message recording equipment, automatic telephone call forwarding equipment, automatic answering data entry systems, and other telephone devices used in association with modem equipment. Telephone answering machines perform the basic function that they automatically answer calls incoming on a telephone line if it is not answered first, play a prerecorded outgoing message to the calling party, and then record any message the calling party leaves. A typical telephone answering machine is a stand-alone device coupled to a telephone line. This type of answering machine typically includes circuitry for detecting a ringing signal on the telephone line indicating the presence of an incoming telephone call, answering the call by taking the line off-hook, playing an outgoing or "greeting" message, recording an incoming message, and hanging up the line in order to respond to a subsequent telephone call. The greeting and incoming recorded messages typically are recorded in the analog domain using one or more conventional audio tapes. The machine may have a display for indicating the number of messages received and the time and date they were received. A telephone with an answering function or mode which automatically records the message of a caller on a recording medium like a cassette tape or an endless tape when nobody is available to answer the telephone. Telephones of this type have an answer mode switch. When this switch is on, the phone mode is changed to the answering mode when receiving a call, and when the switch is off, the phone mode is set to a normal phone mode. Telephone answering machines may also include circuitry for enabling remote-control operation of various ones of the machine's functions (e.g., playback of recorded messages, fast forwarding and rewinding of recorded messages, recording a new greeting message, and so forth). The owner may call his or her home telephone number, wait for the answering machine to answer the call, and then enter a DTMF access code. If the answering machine recognizes the access code, it will allow the user to retrieve messages, delete messages, turn the machine on or off, and perform other control functions. Telephone answering devices are commonly controlled by microprocessors. The microprocessor typically controls a multiplicity of peripheral components of the telephone answering device which may include, for instance, an LCD or LED display, a recording and playback device, indicator lights, a DTMF (dual tone multi-frequency) receiver and an audio controller.

A digital answering machine is used to answer a telephone and store voice messages in an internal memory. A digital answering machine stores messages in solid state memory, rather than on magnetic tape. The use of an internal digital memory eliminates the need for the magnetic tape cassette that was commonly used in earlier answering machines. One of the most recent advances in telephone answering technology is the use of a memory device, such as a random access memory (RAM) or a read only memory (ROM) which is an integrated semiconductor device, instead of magnetic tape for the storage of incoming and outgoing voice messages. The elimination of mechanical parts needed for transporting the tape increases reliability over tape answering machines. The integrated circuits necessary for implementing a digital answering machine require far less physical space than a tape answering machine. Using digital rather than analog means for storing voice messages provides for a more reliable answering machine due to more consistent audio quality, elimination of the problems inherent with moving mechanical parts and also elimination of problems caused by malfunction or breakage of the magnetic tape itself. Having messages stored in an integrated circuit chip also allows the user to selectively access a specific message more quickly and easily than if the messages were stored on a cassette tape. The digital answering machine may also perform voice synthesis from data stored in memory. A synthesized voice message may be provided as a time and date stamp for recorded messages. To reduce physical memory requirements, voice data are preferably compressed for storage and decompressed for playback. Digital memory storage requires the conversion of an analog voice signal generated by a microphone or phone line into a digital representation. In digital answering machines, the digitized signal of a recorded acoustical message is reduced from the data quantity that recorded with optimal conversion to a lesser data quantity in order to save on the cost of required memory. For storing digital data in memory, the analog speech signal is digitized at a predetermined sampling rate in a first step. The resultant data stream is compressed in a second step with the aid of a data or speech compression process. The data stream reduced by the data compression is then recorded in a third step in a digital memory.

Telephone answering machines are now commonly in use and include a number of features which allow a user to screen calls, intercept calls, play back recorded messages, record an announcement, among others. A telephone answering machine is usually triggered by incoming ring signals when the number of ring signals exceed a predetermined number set by the user or manufacturer of the machine. Telephone answering systems are programmed so that if the user does not pick up his telephone from the cradle within a prescribed number of ringing bursts announcing an incoming cal. The control circuitry in answering machines will automatically place an off-hook condition on the telephone line, whereupon the user's prerecorded announcement will be sent to the caller, requesting him to leave his message. The recorder is then reverted to record mode to record the incoming message, thereafter shutting itself off automatically after a given period of time. In addition to recording such incoming messages, the answering machine has the capability to play back the recorded messages later over a loudspeaker on the answering machine. Such machines are also normally provided with volume control which will either mute the loudspeaker completely, or allow it to play at a selected volume. This will allow the user at his option to listen to the incoming message, and if he decides that he wishes to converse with the caller. Some telephone answering systems may offer the caller additional choices, such as the ability to access individual extensions by dialing extension numbers or individual persons or departments by spelling the person's or department's name on the caller's telephone keypad. Telephone answering systems may also offer a caller the ability to connect to a backup person in the absence of the party called, the person to whom the call is directed. An answering machine with toll saver function can know whether or not a new incoming message has been recorded from an outside location by counting the number of the generated ring sounds for the automatic answering telephone answering apparatus. If there is at least a incoming message which has not been heard, the automatic answering telephone answering apparatus responses the call after it has received the ring signal twice.

An answering machine may have limited available capacity on which to record callers' audio message. Recording capacity may be measured by the answering system, as in total number of messages recorded, duration of each message recorded, or total duration of all messages recorded. Upon receiving/recording a message, the answering machine may provide an indication to a user that such message has been received or recorded. Such indication may be provided by a light-type device or an audible alarm-type device which may be an integral part of or coupled to the answering machine. In digital answering machines, the digital speech recording is done with a fixed data compression rate. The ratio between the incoming data stream per unit of time and the data stream per unit of time present after the data compression is called the data compression rate. A high data compression rate accordingly achieves a major reduction in data volume as a result of the compression. Telephone answering devices may be connected to a computer which retrieves stored messages in the telephone answering device. Other types of answering machines, called voice mail systems, serve a plurality of users each having his or her own individually controlled and accessible voice mailbox. Each voice mailbox may be accessed from substantially any other remotely located telephone, either within or without the dwelling. More recently, answering machines have been incorporated into the base stations of cordless telephones and the user has been able to access the answering machine features using a remote cordless handset.