Time-axis compression-expansion devices for sound signals

A time-axis compression-expansion device for use in reproducing an originally recorded signal stored in a recording medium, said device comprising:

• variable rate transducer means for reproducing said originally recorded sound signals at a frequency pitch and speed different from the pitch and speed used in recording and for producing a reproduced sound signal, said different frequency pitch adversely effecting the intelligibility of said reproduced sound signal;
• time-axis compression-expansion processor means for changing the tone of said reproduced sound signal to correspond said tone to the tone of said originally recorded sound signal, thereby forming a converted sound signal including,
• delta modulation means for converting said reproduced sound signal into a digital input signal;
• and
• means for modifying said digital input signal to thereby form a converted digital signal;
• and
• digital-to-analog converter means for changing said converted digital signal into an analog converted sound signal;
• and
• means for converting said converted sound signal into an audible output having a frequency content similar to said originally recorded signal but having a speed different from the speed of said originally recorded signal;
• said time-axis compression expansion processor means modifying said digital input signal so as to change the tone of said reproduced signal to correspond to the tone of said originally reproduced signal;
• means for presenting said reproduced sound signal from said variable rate transducer means directly to said means for converting by bypassing said time-axis compression-expansion processor means when said speed of reproduction is substantially the same as said speed used in recording.