Audio reproduction utilizing a bilevel switching speaker drive signal
First Claim
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1. Apparatus for generating a digital speaker drive signal from digitally encoded audio samples, comprising:
- error propagation means for determining an error between an audio level represented by a digitally encoded sample of a sequence of digitally encoded samples and an audio level represented by a speaker control signal corresponding to said digitally encoded sample, each of said digitally encoded samples having a value corresponding to successive audio levels in an audio signal, respectively, and for altering the values of adjacent succeeding digitally encoded samples by combining predetermined portions of said error with a predetermined number of said adjacent succeeding digitally encoded samples for generating a sequence of error compensated digital samples representative of said audio signal;
conversion means coupled to said error propagation means for converting said sequence of error compensated digital samples to a sequence of bits corresponding on a one-to-one basis to said sequence of error compensated digital samples; and
control means coupled to said conversion means and responsive to said sequence of bits for producing a fixed frequency digital speaker drive signal.
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Abstract
Speech and other audio output is produced from a digitally driven speaker which is turned on and off by a digital control signal derived from a digitally sampled audio input. Digitally encoded samples of an audio signal are converted to a sequence of bits, 1'"'"'s and 0'"'"'s, to control the application of a fixed frequency ultrasonic drive signal to a personal computer speaker. Prior to the signal conversion, the digital samples are compensated utilizing error propagation techniques for audio errors introduced by the conversion from audio levels to full on or full off speaker control bits.
35 Citations
15 Claims
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1. Apparatus for generating a digital speaker drive signal from digitally encoded audio samples, comprising:
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error propagation means for determining an error between an audio level represented by a digitally encoded sample of a sequence of digitally encoded samples and an audio level represented by a speaker control signal corresponding to said digitally encoded sample, each of said digitally encoded samples having a value corresponding to successive audio levels in an audio signal, respectively, and for altering the values of adjacent succeeding digitally encoded samples by combining predetermined portions of said error with a predetermined number of said adjacent succeeding digitally encoded samples for generating a sequence of error compensated digital samples representative of said audio signal; conversion means coupled to said error propagation means for converting said sequence of error compensated digital samples to a sequence of bits corresponding on a one-to-one basis to said sequence of error compensated digital samples; and control means coupled to said conversion means and responsive to said sequence of bits for producing a fixed frequency digital speaker drive signal. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for generating a digital speaker control signal from digitally encoded audio samples, comprising the steps of:
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determining an error between an audio level represented by a digitally encoded sample of a sequence of digitally encoded samples and an audio level represented by a speaker control signal corresponding to said digitally encoded sample; combining predetermined portions of said error with adjacent succeeding digitally encoded samples of said sequence of digitally encoded samples for generating a corresponding sequence of error compensated digital samples; converting said sequence of error compensated digital samples to a sequence of bits corresponding on a one-to-one basis to said sequence of error compensated digital samples; and producing a fixed frequency digital speaker drive signal in accordance with said sequence of bits. - View Dependent Claims (8, 9, 10)
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11. Apparatus for generating a digital speaker drive signal from a sequence of digitally encoded audio samples, comprising:
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first memory means for storing a set of groups of bits, each of said groups of bits associated with a predefined audio level, each said group of bits corrected for the error between said associated predefined audio level and the audio level of a speaker control signal corresponding to said associated predefined audio level, said first memory means responsive to an input sequence of digitally encoded audio samples, each of said digitally encoded audio samples corresponding to the audio level of successive samples in an audio signal, for outputting a sequence of said groups of bits, each of said groups of bits in said sequence of groups of bits corresponding on a one-to-one basis, respectively, with each of said digitally encoded audio samples; and control means coupled to said first memory means and responsive to said sequence of groups of bits for producing a fixed frequency digital speaker drive signal. - View Dependent Claims (12, 13, 14, 15)
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Specification