Digital data converter
First Claim
1. A decoder for generating an analog signal from a digital representation thereof, said digital representation having been produced by an encoder which encodes an input signal of limited bandwidth into a delta modulation bit-stream at a sample rate, and stepsize information, said input signal having been encoded in accordance with said stepsize information to produce said delta modulation bit-stream, comprising:
- (a) digital circuit means for decoding said stepsize information into a digital stepsize control signal,(b) digital demodulator means for converting said delta modulation bit-stream into a multi-bit intermediate digital signal in response to said stepsize control signal, such that said multi-bit intermediate digital signal represents said analog signal in a pulse code modulation format,(c) digital-to-analog converter means for converting said multi-bit intermediate digital signal into a sampled analog signal, and(d) low-pass filter means connected to the output of said digital-to-analog converter means for producing said analog signal from said sampled analog signal,whereby said analog signal will be substantially similar to said input signal.
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Abstract
A decoder for recovering an analog signal from its digital representation produced by an encoder employing adaptive-delta-modulation first decodes audio bit-stream (17) in the digital domain with digital delta demodulation (15), to a pulse-code-modulation (PCM) format digital signal. Post-processing (35), complementary to encoder processing is performed digitally on the PCM signal. The output from post-processor (35) is up-sampled, and using delta modulation, a noise shaped single-bit highly oversampled output is produced by converter (14). Applying the single-bit output to lowpass filter (11) re-constructs the decoded analog signal, which is audio output (12). By fully exploiting digital signal processing techniques, the decoder can be manufactured at low cost and exceed the performance of existing analog implementations.
203 Citations
31 Claims
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1. A decoder for generating an analog signal from a digital representation thereof, said digital representation having been produced by an encoder which encodes an input signal of limited bandwidth into a delta modulation bit-stream at a sample rate, and stepsize information, said input signal having been encoded in accordance with said stepsize information to produce said delta modulation bit-stream, comprising:
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(a) digital circuit means for decoding said stepsize information into a digital stepsize control signal, (b) digital demodulator means for converting said delta modulation bit-stream into a multi-bit intermediate digital signal in response to said stepsize control signal, such that said multi-bit intermediate digital signal represents said analog signal in a pulse code modulation format, (c) digital-to-analog converter means for converting said multi-bit intermediate digital signal into a sampled analog signal, and (d) low-pass filter means connected to the output of said digital-to-analog converter means for producing said analog signal from said sampled analog signal, whereby said analog signal will be substantially similar to said input signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A decoder for generating an analog signal from a digital representation thereof, where said digital representation is produced by an encoder that passes an input signal having a limited bandwidth through a variable spectral pre-emphasis to produce a pre-emphasized signal, and encodes said pre-emphasized signal into (a) a delta modulation bit-stream at a sample rate, said delta modulation bit-stream representing said pre-emphasized signal, (b) a stepsize bit-stream representing a variable stepsize applied in the production of said delta modulation bit-stream, and (c) a spectral bit-stream representing the bandwidth of said variable spectral pre-emphasis, comprising:
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(a) first digital circuit means for decoding said stepsize bit-stream into a stepsize control signal, (b) second digital circuit means for decoding said spectral bit-stream into a spectral control signal, (c) digital demodulator means for converting said delta modulation bit-stream into a multi-bit intermediate digital signal in response to said stepsize control signal, said multi-bit intermediate digital signal representing said pre-emphasized signal in a pulse code modulation format, (d) digital de-emphasis filter means having a bandwidth that varies in response to said spectral control signal connected to the output said digital demodulator means for producing a de-emphasized digital signal, (e) digital-to-analog converter means for converting said de-emphasized digital signal into a sampled analog signal, and (f) low-pass filter means connected to the output of said digital-to-analog converter means for producing said analog signal from said sampled analog signal, whereby said analog signal will be substantially similar to said input signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method for generating an analog signal from a digital representation thereof, said digital representation including a delta modulation bit-stream at a sample rate, and stepsize information, said delta modulation bit-stream representing an input signal having a limited bandwidth, wherein said input signal has been encoded in accordance with said stepsize information to produce said delta modulation bit-stream, comprising the steps of:
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(a) decoding said stepsize information into a digital stepsize control signal, (b) demodulating said delta modulation signal in response to said digital stepsize control signal, so as to produce a multi-bit intermediate digital signal representing said analog signal in a pulse code modulation format, (b) converting said multi-bit intermediate digital signal into a sampled analog signal, and (c) low-pass filtering said sampled analog signal to produce said analog signal, whereby said analog signal will be substantially similar to said input signal. - View Dependent Claims (26, 27, 28, 29, 30, 31)
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Specification