Audio signal recording and reproducing apparatus utilizing digital data compression and extension

• US 4,910,780 A
• Filed: 07/08/1988
• Issued: 03/20/1990
• Est. Priority Date: 07/14/1987
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Miki, Tsutomu
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/216,539
• Time in Patent Office: 620 Days
• Field of Search: 375/25-33, 381/29-33, 381/36-40, 381/34-35, 364/513.5
• US Class Current: 704/211
• CPC Class Codes: G11B 20/00007 Time or data compression or expansion audio compression based on psychoacoustics G10L19/00; data processing for reproducing audio data at different playback speeds G10L21/04; video compression H04N19/00; data compression per se H03M7/30
• CPC Class Codes: G11C 2207/16 Solid state audio
• CPC Class Codes: G11C 7/16 Storage of analogue signals in digital stores using an arrangement comprising analogue/digital [A/D] converters, digital memories and digital/analogue [D/A] converters
• CPC Class Codes: H03M 3/04 Differential modulation with several bits , e.g. differential pulse code modulation [DPCM] H03M3/30 takes precedence
• CPC Class Codes: H03M 7/30 Compression speech analysis-synthesis for redundancy reduction G10L19/00; for image communication H04N; Expansion; Suppression of unnecessary data, e.g. redundancy reduction

Abstract

An audio signal recording and reproducing apparatus digitizes sound into an electric audio signal, data compresses the signal into compressed data to reduce information quantity, records the compressed data into a semiconductor memory, and reproduces an audio signal from the recorded data. The apparatus includes a plurality of input compression and output extension conversion tables which are used for compression conversion of input signal and extension conversion of output signal, respectively. Input compression and output extension conversion table selection counters are count-controlled by difference data representing the change of the audio signal. The apparatus selects one among a plurality of input compression and output extension conversion tables in accordance with count values of the selection counters. The conversion tables are arranged in sequence and contain successively larger ranges of values.

Claims

1. An audio signal recording and reproducing apparatus comprising:

an analog to digital converter which digitizes sound into a digitized signal;

an input data difference operator connected to receive the digitized signal and to output difference data representing changes in the digitized signal;

means for data compressing the difference data into conversion values to reduce information quantity and for extending the conversion values into reproduced difference data;

a semiconductor memory connected to receive and store the conversion values from the means for compressing and to supply the conversion values to the means for extending;

an output data difference operator connected to receive the reproduced difference data and to output a reproduced digitized signal; and

a digital to analog converter connected to receive the reproduced digitized signal and to output a reproduced output analog signal;

the means for compressing and extending including a plurality of input compression and output extension conversion tables which are used for compression conversion of the difference data into the conversion values and for extension conversion of the conversion values into the reproduced difference data, respectively, each input compression conversion table containing conversion values corresponding to a range of values of difference data, the input compression conversion tables being arranged in succession, the conversion values of each successive input compression conversion table corresponding to a successively larger range of difference data values, the output extension conversion tables being arranged in succession, each successive output extension conversion table containing a successively larger range of values of reproduced difference data corresponding to the conversion values, wherein compression conversion of the difference data into conversion signals includes reading conversion signals out of a selected one of the input compression conversion tables, and wherein extension conversion of the conversion values into reproduced difference data includes reading the reproduced difference data out of a selected one of the output extension conversion tables; and

input compression and output extension conversion table selection counters which contain one of a plurality of count values, each of the plurality of count values corresponding to one of the input compression and output extension conversion tables, respectively, the input compression and output extension selection counters being count-controlled by the difference data and conversion values, respectively, to select the selected one among the plurality of input compression and output extension conversion tables, respectively, which corresponds with the count value contained by the counters.

2. An audio signal recording and reproducing apparatus as defined in claim 1 wherein said input compression and output extension conversion table selection counters contain one of a predetermined set of successive count values, the plurality of input compression and output extension conversion tables include one input compression conversion table corresponding to each of the successive count values of the input compression conversion table selection counter and one output extension conversion table corresponding to each of the successive count values of the output extension conversion table selection counter, the apparatus further comprising means for up-counting and for down-counting the count values in the selection counters between successive count values and for leaving the count values unchanged in accordance with whether the conversion value is within a predetermined range.

3. An audio signal recording and reproducing apparatus comprising:

an input data difference operator connected to receive a sequence of successive digital samples of an input audio signal and to output first difference values between successive samples;

a plurality of input compression conversion tables, each input compression conversion table containing a series of conversion values corresponding to a range of the first difference values, different input compression conversion tables containing conversion values corresponding respectively to different first difference values, the input compression conversion tables arranged in succession such that the conversion values of each successive input compression conversion table correspond to a successively larger range of difference values;

an input difference comparison section connected to receive each of the sequence of first difference values, to compare each first difference value with the contents of one of the plurality of input compression conversion tables and to compression convert each first difference value to produce compressed data including a conversion value from one of the input compression conversion tables;

a memory device connected to receive and store the compressed data;

a plurality of output extension conversion tables, each output extension conversion table containing a series of second difference values corresponding to a series of conversion values, different output extension conversion tables containing different ranges of difference values, the output extension conversion tables arranged in succession such that each successive output extension conversion table contains a successively larger range of difference values;

an output data difference operator connected to receive a sequence of said second difference values corresponding to conversion data stored in the memory device, the second difference values read from the output extension conversion tables, and to output a sequence of digitized output signals, each of the sequence of digitized output signals differing from a previous digitized output signal by a corresponding one of the second difference values;

an input compression conversion table selection counter containing one of the series of input compression conversion table selection values, each input compression converstion table selection value corresponding to one of the plurality of input compression conversion tables, wherein the input difference comparison section compression converts a first difference value to produce compressed data by reading a conversion value corresponding to the first difference value of an input compression conversion table corresponding to the input compression conversion table selection value contained in the input compression conversion table selection counter, and updates the input compression conversion table selection counter by up-counting or down-counting the input compression conversion table selection value based upon whether the first difference value exceeds a predetermined maximum value or is exceeded by a predetermined minimum value, respectively; and

an output extension conversion table selection counter containing one of the series of output extension conversion table selection values, each output extension converstion table selection value corresponding to one of the plurality of output extension conversion tables, wherein the compressed data is converted into a sequence of second difference values by reading a second difference value corresponding to the compressed data out of an output extension conversion table corresponding to the output extension conversion table selection value contained in the output extension conversion table selection counter, and the output extension conversion table selection counter is updated by up-counting or down-counting the output extension conversion table selection value based upon whether the second difference value exceeds a predetermined maximum value or is exceeded by a predetermined minimum value, respectively.