Decreasing time duration of recorded speech

Abstract

Disclosed is apparatus for and a method of decreasing the time duration of playback of recorded speech without distortion. Speech recorded at a normal rate is played back at a higher rate using two variable length buffers in alternating fashion to receive sampled speech segments. Threshold analysis logic circuitry is provided to continually compare the output voltage levels of both buffers and to switch the output between the buffers to a using device when the voltage level of both buffers is approximately zero and of an equal amplitude. In this way output to the using device consists of segments from both buffers joined with a minimum of generated noise and no associated dead zone without regard to any predetermined segment length.

What is claimed is: 
     
       1. In a system for time compression of prerecorded speech signals which are played back at a rate greater than that at which they were recorded and in which the input speech is loaded alternately into first and second buffers and output from the buffers is alternatively applied to a using device, said system including means for loading one of said buffers while the other is providing an output to said using device, the improvement comprising:   means for changing the source of output applied to said using device from said fist buffer to said second buffer when the output level of both of said buffers .Iadd.is substantially equal and .Iaddend.falls within a predetermined range .Iadd.of a zero crossing.Iaddend..  .[.2. The system of claim 1 wherein the means for the source of output further includes means for determining when the output level of both of said buffers is substantially equal..]. .[.3. The system of claim 1 wherein said output levels of said buffers move about a zero reference and wherein the predetermined range has its midpoint at substantially the zero level..].   
     
     
           The .[.speech.]. system of claim .[.3.]. .Iadd.1 .Iaddend.further wherein the width of said range is less than two percent of the maximum amplitude of said output levels.  .[.5. The speech system of claim 4 wherein the output from said first buffer to said using device is terminated when said first buffer is empty and the output of said second 
     
     
        buffer is then applied to said using device..]. 6. Apparatus for time compressing speech signals which includes an input terminal for receiving the speech signals, an analog to digital converter connected to the input terminal, first and second dynamic storage means connected to the analog to digital converter, means for reading the signals into either the first or second storage means at a first rate, means for reading out from either the first or second storage means at a second rate, first and second digital to analog converters connected to the outputs of the first and second storage means, means for comparing the outputs of the first and second digital to analog converters, the improvement comprising .Iadd.said means for comparing further including first comparator means for determining equality of the outputs of said digital to analog converters, second comparator means for determining if the output of one of said digital to analog converters is less than a predetermined reference value, third comparator means for determining whether the output from said second digital to analog converter is greater than a second predetermined reference value, and means responsive to said first, second and third comparator means for developing a change signal when the outputs from said first and second digital analog converters are equal and within the predetermined range; and.Iaddend.: means responsive to said means for comparing for alternating reading in and reading out when the output of said digital to analog converters is .Iadd.substantially equal and .Iaddend.within a certain predetermined range .Iadd.of a zero crossing.Iaddend., whereby segments of speech signals from said first and second dynamic storage means are joined with a minimum of generated noise.  .[.7. The apparatus of claim 6 wherein the means for comparing the outputs of said first and second digital to analog converters includes first comparator means for determining equality of the outputs of said digital to analog converters, second comparator means for determining if the output of one of said digital to analog converters is less than a predetermined reference value, third comparator means for determining whether the output from said second digital to analog converter is greater than a second predetermined reference value, and means responsive to said first, second and third comparator means for developing a change signal when the outputs from said first and second digital analog converters are equal and within the predetermined range..].   
     
     
        . The apparatus of claim .[.7.]. .Iadd.1 .Iaddend.wherein said first and second reference values define a narrow window with zero at its center. 
     
     
           A method of joining time compressed recorded speech signals in a substantially noise free manner comprising the steps of: sampling speech signals;   storing said sampled signals at a first rate in one of a pair of storage elements;   reading out said sampled speech signals at a second rate from the other of the pair of storage elements;   continually comparing output voltages from each storage element;   switching input and output clocks applied to the storage elements when the voltage levels from each storage device are substantially equal and within a predetermined range of a zero crossing; and switching from one to the other of the storage elements as the source of output applied to a using device.