US 4,366,471 AGranted

Variable speed digital reproduction system using a digital low-pass filter

AssigneeVictor Company of Japan, Ltd.

InventorMasao Kasuga

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Abstract

A variable speed reproduction system includes a memory in which analog signal is stored as sampled digital data. A variable frequency digital low-pass filter is receptive of the data read out of the memory. A counter provides a binary representation of a count value of time base clock pulses to a comparator for detecting a coincidence with a variable speed setting of a variable resistor. The output of the comparator resets the counter and is used as a source of reading the data out of the memory. The cut-off frequency of the digital filter is controlled in response to the setting of the resistor so that the high frequency component of the analog equivalent of the input digital data which is higher than one-half of the data reading frequency is eliminated to prevent foldover distortion noise which might occur as a result of the difference between the recording and reproducing speeds. The data read out of the memory is fed to a digital-to-analog converter at a constant frequency and the quantum noise of the output data is filtered out by an analog low-pass filter.

Claims8

Dependent claims

A system for reproducing an analog signal which is stored as sampled data in memory means at a variable speed which may differ from the speed at which the analog signal is sampled and recorded into said memory means, comprising:

a clock source for generating clock pulses occurring at a frequency substantially corresponding to the speed at which said sampled data is recorded into said memory means;
a binary counter for counting said clock pulses to generate a first binary output representing the count value of said clock pulses;
means for generating a second binary output representing said variable speed;
means for detecting a match between said first and second binary outputs to reset said binary counter to an initial count value and reading the stored data out of said memory means in response to the occurrence of the detected match;
a digital low-pass filter for eliminating a high frequency component of the analog equivalent of the sampled data, the cut-off frequency of said filter being variable in response to the value of said second binary output so that the cut-off frequency corresponds substantially to one-half of the frequency at which said detected match occurs;
and
a digital-to-analog converter for converting a filtered signal from said digital low-pass filter at a constant frequency into a corresponding analog signal.

4 more elements

Dependencies are inferred from the claim text.