Speech digitization system
First Claim
1. A de-digitizer for use in a companded speech digitization system including a digitizer circuit for generating a digital approximation of a bipolar analog audio input signal, the de-digitizer reconstructing the analog input signal from a pulse code modulated digital input signal representing a digital approximation of said analog waveform, including:
- generator means responsive to said digital input signal for generating an amplitude function signal in accordance with said digital input signal, including first means for converting said digital input signal to a corresponding first analog signal, a bias network for producing a predetermined offset signal and an amplifier having associated therewith a predetermined gain greater than one and less than or equal to five and having said first analog signal connected to its positive input and said predetermined offset signal connected to its negative input;
decoder means for generating the analog input signal by multiplying said digital input signal with said amplitude function signal.
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Accused Products
Abstract
A speech digitization system including novel encoder and decoder circuits that minimizes the number of resolution bits required to produce a given level of speech quality by optimizing the information content of the digital output signal from the encoder. This is accomplished by providing a companded speech digitization system that includes an amplitude function generator which is adapted to produce an amplitude function signal that maintains substantial duty cycles on the digital output signal over the entire audio amplitude range. Included in the novel amplitude function generator is a unique bias network that serves to center the duty cycle swing of the digital output signal from the encoder around 50% where the information content of the signal is statistically maximized.
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Citations
11 Claims
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1. A de-digitizer for use in a companded speech digitization system including a digitizer circuit for generating a digital approximation of a bipolar analog audio input signal, the de-digitizer reconstructing the analog input signal from a pulse code modulated digital input signal representing a digital approximation of said analog waveform, including:
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generator means responsive to said digital input signal for generating an amplitude function signal in accordance with said digital input signal, including first means for converting said digital input signal to a corresponding first analog signal, a bias network for producing a predetermined offset signal and an amplifier having associated therewith a predetermined gain greater than one and less than or equal to five and having said first analog signal connected to its positive input and said predetermined offset signal connected to its negative input; decoder means for generating the analog input signal by multiplying said digital input signal with said amplitude function signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A de-digitizer for use in a companded speech digitization system including a digitizer circuit for generating a digital approximation of a bipolar analog audio input signal, the de-digitizer reconstructing the analog input signal from a pulse code modulated n-bit parallel digital input signal representing a digital approximation of said analog waveform, including:
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a logic gate for inverting the most significant bit (MSB) from said n-bit parallel digital input signal, (n-1) exclusive-OR logic gates for logically comparing said inverted MSB to each of said remaining (n-1) bits in said n-bit digital signal, filter means for producing a first analog signal comprising (n-1) parallel-connected weighting resistors each connected to the output of one of said exclusive-OR gates and a capacitor connected between said weighting resistors and ground, a bias network for producing the predetermined offset signal, an amplifier having a predetermined gain greater than one and less than or equal to five and having said first analog signal connected to its positive input and said predetermined offset signal connected to its negative input, said amplifier producing said amplitude function signal at its output; and multiplying digital-to-analog conversion means having said n-bit digital input signal connected to its parallel digital input and said amplitude function signal connected to its multiplying input for generating said analog input signal by converting said n-bit digital input signal to a corresponding analog signal and scaling said analog signal in accordance with the magnitude of said amplitude function signal. - View Dependent Claims (10, 11)
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Specification