1. Field of the Invention
The present invention relates to a digital audio system which transmits or utilizes, as a modulation signal of a recording/playing back operation, a digital signal obtained by sampling an audio signal at predetermined time intervals, and more specifically to a digital audio system of this type provided with automatic fade in and fade out operations.
2. Description of Background Information
Digital audio systems are designed, for example, such that an audio input signal is sampled at predetermined time intervals and the sampled value is subsequently treated by a quantization process. The quantized signal is then modulated by a modulation process such as a PCM (Pulse Code Modulation) process in which an input signal is represented by combinations of pulses having either one of two binary values 0 and 1. The thus obtained digital signal, that is the PCM signal, is utilized for transmission or recording/playing back of the audio signal.
On the other hand, in playing back or recording audio signals, it is desirable that fade in and fade out operations are provided so that the volume of a desired sound is gradually reduced to remove the desired sound from a predetermined program, or the volume of a desired sound is gradually increased to insert the desired sound into the predetermined program.
In conventional digital audio systems of this type, if a fade in or fade out operation is required, it was necessary to manipulate a control means such as a volume control of an amplifier or a record level control of a tape recorder. Therefore, automatic fade in and fade out operations are desirable in order to eliminate rather troublesome manual operations by an operator or to eliminate annoying audio responses during the fade in or fade out operation which has often been caused by excessive rapid change of the volume of the sound.