High speed voice replay via digital delta modulation

• US 4,091,242 A
• Filed: 07/11/1977
• Issued: 05/23/1978
• Est. Priority Date: 07/11/1977
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Franaszek, Peter Anthony, Carrubba, Francis Paul, Daniels, Walter Edgar Jr.
• Primary Examiner(s): Brown, Thomas W.
• Assistant Examiner(s): Kemeny, E. S.
• Application Number:
  US05/814,591
• Time in Patent Office: 316 Days
• Field of Search: 179/1 SA, 179/1 SM, 179/15.55 T, 325/38 B, 332/11 D, 360/8, 358/133, 358/141, 358/146, 358/260, 358/261
• US Class Current: 704/501
• CPC Class Codes: G10L 21/00 Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility G10L19/00 takes precedence
• 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: G11B 20/10527 Audio or video recording; Data buffering arrangements G11B20/12 - G11B20/18 take precedence
• CPC Class Codes: G11B 2220/20 Disc-shaped record carriers
• CPC Class Codes: G11B 27/005 Reproducing at a different information rate from the information rate of recording for television signals H04N5/783
• CPC Class Codes: H03M 3/02 Delta modulation, i.e. one-bit differential modulation H03M3/30 takes precedence
• CPC Class Codes: H04B 1/66 for reducing bandwidth of signals; for improving efficiency of transmission H04B1/68 takes precedence

Abstract

A method of and apparatus for time compression and changing the readout speed of a delta modulation encoded audio signal. The encoded audio signal has portions selectively deleted therefrom in accordance with detected zero crossovers of the same sign which occur in a predetermined timing sequence. The encoded audio signal which has had portions selectively deleted therefrom is decoded, with the undeleted decoded portions being joined. The undeleted portions have the same gain factor where joined, thereby eliminating step transients.

Claims

1. In a delta modulator audio replay system, the combination comprising:

means for delta modulation encoding of a provided audio signal;

means for determining the positive and negative zero crossovers of the delta modulation encoded audio signal;

means for selectively deleting portions of the delta modulation encoded audio signal which occur between zero crossovers having the same sign, and which occur in a predetermined timing sequence;

means for storing the delta modulation encoded audio signal which has had portions selectively deleted therefrom; and

means for delta modulation decoding of the stored delta modulation encoded signal which has had portions selectively deleted therefrom, including means for joining the undeleted decoded portions, with said undeleted decoded portions having the same gain factor where joined.

2. In a delta modulator audio replay system, the combination comprising:

means for providing an audio signal;

means for delta modulation encoding said audio signal;

a first delta modulator decoder for decoding the delta modulation encoded audio signal, and for determining the gain factor for each decoded segment of said audio signal;

a zero crossover detector for detecting the positive and negative crossovers of the decoded audio signal from said first delta modulator decoder;

timing means for providing timing signals, with the generation of said timing signals being controlled at least in part by the detected zero crossovers;

a second delta modulator decoder;

first and second storage means, with said delta modulation encoded audio signal being read into and out of said first and second storage means under control of said timing signals, with said delta modulation encoded signal being read into said first register when the contents of said second register is being read into said second delta modulator decoder and vice versa, with certain portions of said delta modulation encoded audio signal being deleted in accordance with the generation of said timing signals and as a function of the detected zero crossovers, prior to being stored in said first and second storage means; and

wherein the gain factor for one segment of the delta modulation encoded audio signal decoded in said second delta modulation decoder is controlled by said second delta modulation decoder, and the gain factor for the following segment of speech where joined to said one segment of speech is controlled by the determined gain factor from said first delta modulator decoder.

3. In a delta modulator audio replay system, the combination comprising:

means for providing an audio signal;

means for delta modulation encoding said audio signal;

means for storing said delta modulation encoded audio signal;

a first delta modulator decoder for decoding the stored delta modulation encoded audio signal, and for determining the gain factor for each decoded segment of said audio signal;

a first storage register for storing the determined gain factor from said first delta modulator decoder;

a zero crossover detector for detecting the positive and negative crossovers of the decoded audio signal from said first delta modulator decoder;

a mod-2 counter which is set to a first state when a first group of timing signals is to be generated, and which is set to a second state when a second group of timing signals is to be generated;

a positive crossover flip flop which changes state in response to the detection of a positive crossover by said zero crossover detector;

a negative crossover flip flop which changes state in response to the detection of a negative crossover by said zero crossover detector;

a first delete flip flop which changes state in response to a change of state of one of said positive and negative crossover flip flops, and said mod-2 counter being in said second state;

a second delete flip flop which changes state in response to a change of state of one of said positive and negative crossover flip flops, and said mod-2 counter being in said first state;

timing means for providing said first and second group of timing signals in response to said mod-2 counter being in said first and second states respectively, with said timing means being controlled at least in part by said zero crossover detector, said positive and negative crossover flip flops, and said first and second delete flip flops;

a second delta modulator decoder for decoding undeleted portions of speech and for determining the gain factor for each undeleted portion;

second and third storage registers, with the stored delta modulation encoded audio signal being read into and out of said second and third storage registers under control of said first and second groups of timing signals respectively, with said stored delta modulator encoded signal being read into said second storage register when the contents of said third storage register is being read into said second delta modulator decoder and vice versa, with certain portions of said stored delta modulation encoded audio signal being deleted prior to being stored in said second and third storage registers, with the deletion of said certain portions being controlled in accordance with the states of said first and second delete flip flops, respectively; and

wherein the gain factor for one segment of the delta modulation encoded audio signal decoded in said second delta modulation decoder is controlled by said second delta modulation decoder, and the gain factor for the following segment of undeleted speech where joined to said one segment of speech is controlled by the determined gain factor stored in said first storage register.

4. A method of changing the readout speed of a delta modulated audio signal, said method comprising the steps of:

encoding a provided audio signal in a delta modulation code;

storing the delta modulation coded audio signal;

determining the positive and negative zero crossovers of the delta modulation coded signal;

deleting portions of the stored delta modulation coded audio signal which occur between zero crossovers having the same sign at predetermined intervals; and

decoding the stored delta modulation coded signal which has had portions deleted therefrom, including joining the undeleted decoded portions, with said undeleted decoded portions having the same gain factor where joined.

5. A method of controlling the readout speed of a delta modulated audio signal, said method comprising the steps of:

encoding a provided audio signal in a delta modulation code;

decoding the delta modulation encoded audio signal in a first delta modulator decoder, including determining the gain factor for each segment of the encoded audio signal;

detecting the positive and negative zero crossovers of the decoded audio signal from said first delta modulator decoder;

providing timing signals, with the generation of said timing signals being controlled at least in part by the detected zero crossovers;

deleting certain portions of the encoded audio signal in accordance with the provision of said timing signals and said detected zero crossovers;

reading said encoded audio signal, with said certain portions deleted, into and out of first and second storage means into a second delta modulator decoder under control of said timing signals, with said second delta modulator decoder determining the gain factor for each undeleted segment of speech, with said encoded audio signal with said portions deleted being read into said first storage means when the contents of said second storage means is being read into said second delta modulator decoder and vice versa; and

decoding the undeleted portions of said audio signal in said second delta modulator decoder, including joining the undeleted portions with the same gain where joined, with the gain factor for one segment being determined by said second delta modulator decoder, and the gain factor for the following segment where joined, is determined by said first delta modulator decoder.