Volume control for a personal computer internal speaker

Details Volume control for a personal computer internal speaker Volume control for a personal computer internal speaker

1994-05-10

1997-09-09

Oh, Minsun

Electrical audio signal processing systems and devices

Including amplitude or volume control

With manual volume control

381104, H03G 300

Patent

active

056664311

ABSTRACT:
Method and apparatus for controlling the volume of an internal PC speaker. In the present invention, pulse width modulation (PWM) techniques are used to selectively reduce the signal power generated at the speaker. By substituting a high frequency signal having a symmetric duty cycle for portions of the digital audio signal, the average signal power is reduced. The frequency of the substitute signal is much higher than the speaker bandwidth, contributing negligible power to the output. The ratio of audio signal to high frequency signal determines the output signal level. In the preferred embodiment of the present invention, a three bit counter is used to separate the audio signal into intervals having eight states apiece. A signal providing -6 dB of attenuation is generated by substituting the toggling output from the least significant bit of the counter during four out of the eight states. A signal providing -12 dB of attenuation is generated by substituting the same toggling output during six out of the eight states. A multiplexer is provided to select between the two attenuated signals, an unattenuated signal and a DC signal (off).

REFERENCES:
patent: 5150415 (1992-09-01), Jaffee

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