A method for determining intensity characteristics of background noise during speech pauses of speech signals includes determining a proportion of speech pauses in the undisturbed source speech signal so as to define a frequency threshold. The disturbed speech signal is divided into short successive signal elements, an intensity value is determined for each of the signal elements, and a cumulative relative frequency distribution is formed from the determined intensity values of the signal elements. The cumulative relative frequency distribution is used to determine an intensity threshold value which corresponds to the defined frequency threshold. At least one intensity characteristic of the background noise during the speech pauses is determined using a region of the cumulative relative frequency distribution below the intensity threshold value.

An improved voice activity detection system and method is provided for use in speakerphones and other voice activated systems. To facilitate switching between various operating modes, the voice activity detection scheme utilizes a new voice energy term which is based on an integral of the absolute value of a derivative of a speech signal. Voice activity is detected during a silence mode by comparing a first ratio of a current voice energy value to a background noise value with a voice activity threshold value. Voice activity is detected when the first ratio is greater than the voice activity threshold value. Another step involves identifying a direction of the voice activity during a transmit and receive mode by comparing a second ratio of a transmit path voice energy value to a receive path voice energy value with a transmit threshold value and a receive threshold value. When the second ratio is greater than the transmit threshold value, voice activity is present in the transmit path. Similarly, when the second ratio is less than the receive threshold value, then voice activity is present in the receive path. Following the detection of voice activity in one of the paths, the speakerphone or voice activated system begins transitioning to the applicable mode by gradually suppressing the signal in the other path according to the value of the second ratio.

A digital audio player has a removable and interchangeable multi-function module that has at least one operating member. The multi-function interchangeable module interoperates with the body of the digital audio player to provide a plurality of features, which include, but are not limited to, additional memory storage, radio tuner, display, Infrared transceiver and wireless transceiver.

A recording and/or reproducing apparatus includes a microphone, a semiconductor memory, an operating section and a controller. An output signal from the microphone is written in the semiconductor memory and the written signals are read out from the semiconductor memory. The operating section performs input processing for writing a digital signal outputted by an analog/digital converter, for reading out the digital signal stored in the semiconductor memory and for erasing the digital signal stored in the semiconductor memory. The control section controls the writing of the microphone output signal in the semiconductor memory based on an input from the operating section and the readout of the digital signal stored in the semiconductor memory. The control section operates so that, when the signals written in the storage section are read out from it, an input for erasure is entered by the operating section, and the signal being read out from the storage section is erased when, after reading out the signal from the storage section for a pre-set period, an input for erasure is again entered from the operating section.

A portable sound recording device includes a microphone, a speaker and recording/playback circuitry connected to the microphone and speaker. The recording/playback circuitry includes a recording medium such as a removable solid state memory card. A control circuit controls operation of the recording/playback circuitry on the basis of input signals generated by a user via an operating switch array. The switch array includes a record switch. If the record switch is actuated for only a brief period of time, a record-lock mode of operation is implemented. If the record switch is actuated for a longer period of time, a momentary-record mode is entered which lasts only as long as the record switch remains in an actuated position.