1. Field of the Invention
The present invention relates to a digital audio signal player, and more particularly to a digital audio signal player having an operation unit freely operated by a user to modulate the output state of the disc audio signal by changing the rotation state of the operation unit.
2. Description of the Related Art
In general, the DJ (diskjockey) in the pub or the like often employs a “scratch” operation mode to play the music. When the user's hand touches the disk to change the rotation direction and speed of the disk, the music at the normal state is interrupted, thereby forming a special audio playing effect. After the user's hand is removed from the disk, the special audio playing effect disappears, and the music is played at the normal state.
A conventional digital audio signal player in accordance with the prior art was disclosed in U.S. Pat. No. 6,618,329-B2 and includes a conductive turntable, and a sensor for sensing the rotating speed and direction of the turntable so that the turntable has a smaller signal at the normal state. When the human body touches the turntable, there is produced a larger signal, named as a glitch below, which is guided by the turntable to be processed by an audio signal processor and a glitch detecting circuit and is then sent to a microprocessor which compares the differential between the smaller signal and the glitch. If the differential is greater than a predetermined value, the microprocessor judges that the turntable is under contact with the human body. Thus, when the user applies a force to rotate the turntable, the sensor detects the rotating speed and direction of the turntable so that the audio signal processor determines the output of the digital music data stored in the memory according to the detected state. Then, the digital music data after processed are converted into an analog format by a digital/analog converter, filtered by a low pass filter and finally played. When the microprocessor and the audio signal processor detect that the larger signal disappears after the human body's leaving the turntable, the music is returned to the normal state.
In conclusion, the conductive turntable being touched by the human body produces a glitch which is processed by the glitch detecting circuit and compared with the original signal to judge if the human body touches the turntable. However, the conventional digital audio signal player is performed in a crowded place and electrically connects with other electronic equipments, such as mixers, loudspeakers or the like. In such a manner, both the human body and other energized electronic equipments produce magnetic fields which produce different glitches to interfere with the detection of the glitch detecting circuit, so that the glitch detecting circuit is hard to judge if the human body touches the turntable exactly.