Abstract: The present invention relates to an apparatus and a method for volume control in digital telephones such as second generation mobile telephone terminals, third generation IMT 2000 image mobile telephone terminals, and ISDN (integrated service digital network) terminals. In particular, an apparatus and a method in accordance with an embodiment of the present invention measure background noise and adjust volume of received sound and/or ring signal accordingly. An embodiment of the present invention measures background noise before ringing ring signal and adjusts volume of ring signal. While communicating, the apparatus automatically adjusts volume of received sound in response to the measured background noise. A telephone terminal in accordance with an embodiment of the present invention includes voice/non-voice determination part, volume measurement part, and gain control part. The voice/non-voice determination part separates pure background noise from composite signal (voice+background noise).

Abstract: The present invention relates to a transmitter and a receiver for speech coding and decoding by using an additional bit allocation method. The transmitter and the receiver according to the present invention realize a voice communication service of high quality by using additional bits permitted in system requirements while using a conventional speech coder as it is. In addition, the transmitter and the receiver according to the present invention have an advantage in that they enable insertion of additional quantization blocks while not changing the structure of the conventional standard speech coder, since they allocate additional bits by applying a multi-stage quantization procedure not in a speech signal domain but in a parameter domain.

Abstract: A method and an apparatus for transmitting a speech signal are provided. A speech signal transmitter includes a quadrature mirror filter, a bas sub-band encoder, an enhancement sub-band encoder, and a network connector. The quadrature mirror filter receives a speech signal, divides the speech signal into an enhancement band speech signal and a base band speech signal, and outputs the enhancement band speech signal and the base band speech signal. The base sub-band encoder receives and encodes the base band speech signal. The enhancement sub-band encoder receives and encodes the enhancement band speech signal. The network connector multiplexes the encoded enhancement band speech signal and the encoded base band speech signal based on the kinds of networks over which speech signals are transmitted, and transmits the multiplexed signals to the networks. A speech signal is multiplexed and transmitted by various methods based on the kinds of networks. Thus, the speech signal can be efficiently transmitted.