VARIABLE DELAY LINE SIGNAL PROCESSOR FOR SOUND REPRODUCTION

• US 3,786,195 A
• Filed: 08/13/1971
• Issued: 01/15/1974
• Est. Priority Date: 08/13/1971
• Status: Expired due to Term

• Current Assignee: The Variable Speech Control
• Original Assignee: Murray M. Schiffman
• Inventors: Schiffman, Murray M.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Leaheey, Jon Bradford
• Application Number:
  US05/171,571
• Time in Patent Office: 886 Days
• Field of Search: 179/15.55T,15.55R,15BW 178/5.4HE,6.6TC,DIG.3
• US Class Current: 704/211
• CPC Class Codes: G10L 21/04 Time compression or expansion
• CPC Class Codes: G11B 21/00 Head arrangements not specific to the method of recording or reproducing
• CPC Class Codes: G11B 5/00 Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor G11B11/00 and G11B13/00 take precedence
• CPC Class Codes: H03H 11/265 with adjustable delay
• CPC Class Codes: H03H 7/30 Time-delay networks analogue shift registers G11C27/04
• CPC Class Codes: H03K 4/502 the capacitor being charged from a constant-current source
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H04B 1/66 for reducing bandwidth of signals; for improving efficiency of transmission H04B1/68 takes precedence
• CPC Class Codes: H04B 1/662 using a time/frequency relationship, e.g. time compression or expansion
• CPC Class Codes: H04B 3/10 by pilot signal

Abstract

An electrical delay line which has variable delay controlled by a signal input thereto is connected in a sound signal channel for signals such as human speech, to compress or expand the sound signal waveform depending on whether the time delay in the line is increased or decreased. By periodically sweeping the delay line from minimum to maximum time delay or vice-versa, repeated segments of a continuous sound signal waveform are processed so that an output audio signal can be obtained having the original frequency components of the signal and occupying a time duration which is equal to or smaller or larger than the original sound sequence with the successive segments of the signal processed by the variable delay line assembled with regard both to the significant parameters of human speech or other coding and the electrical conditions imposed by the system to produce a composite audio signal which is an intelligible replica of the original and substantially free of annoying aberrations introduced by the delay line processor. Variable delay using analog or digital signal storage is also provided.

Claims

1. A processor for electric signals representing coded audible signals such as speech or the like comprising:

means for deriving said electric signals as analog representations of said audible signals with the frequency components of said electric signals related by a given factor to the frequency components of said audible signals;

variable delay line means having an input and an output, said input coupled to said means for deriving said electric signals for propagating representations of said electric signals to said output with controllable time delay;

means for controlling said delay line means for periodic linear variation of said time delay between predetermined delay values; and

means coupled to said output of said delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to unidirectional variation of said time delay for producing output signals reproducible as an audible representation of said electric signals having frequency components altered by substantially said factor to approximate the frequency coMponents of said audible signals.

2. A processor for electric signals representing coded audible signals such as speech or the like comprising:

means for deriving said electric signals as analog representations of said audible signals with the frequency components of said electric signals related by a given factor to the frequency components of said audible signals;

variable delay line means having an input and an output, said input coupled to said means for deriving said electric signals for propagating representations of said electric signals to said output with controllable time delay;

means for controlling said delay line means for periodic linear variation of said time delay between predetermined delay values; and

means coupled to said output of said delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to unidirectional variation of said time delay for producing output signals reproducible as an audible representation of said electric signals having frequency components altered by substantially said factor to approximate the frequency components of said audible signals; and

in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line is returned to an initial predetermined delay value and including means for blanking output signals from said output of said delay line means to substantially zero amplitude during said reset intervals.

3. Apparatus according to claim 2 in which said means for blanking includes means for gradually restoring the amplitude of said output signals to full amplitude after said reset intervals.

4. Apparatus according to claim 1 and including input high pass filter means, said filter means substantially eliminating components of said electrical signals from propagating through said delay line means which are below a frequency approximately equal to said factor times the reciprocal of the period of said linear variation.

5. Apparatus according to claim 4 and including band pass output filter means for limiting said output signals to a predetermined audio bandwidth.

6. Apparatus according to claim 1 and including:

input high pass filter means having adjustable low frequency cutoff interposed between said means for deriving said electric signals and said input of said variable delay line means;

means for adjusting the effective rate of said periodic linear variation to adjust said factor by which frequencies propagated through said delay line are altered; and

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation.

7. Apparatus according to claim 6 in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line is returned to an initial predetermined delay value and including means for blanking output signals from said output of said delay line means to substantially zero amplitude during said reset intervals.

8. Apparatus according to claim 7 in which said means for blanking includes means for gradually restoring the amplitude of said output signals to full amplitude after said reset intervals.

9. Apparatus according to claim 2 in which said means for blanking includes means responsive to the level of said output signals being zero at the beginning of said reset interval to initiate said blanking and means responsive to the level of said output signals being zero at the end of said reset interval to terminate said blanking.

10. Apparatus according to claim 2 and including means for introducing an audio signal segmenT into for combining with said audible representation of said electric signals during said reset interval.

11. A processor for electric signals representing coded audible signals such as speech or the like comprising:

means for deriving said electric signals as analog representations of said audible signals with the frequency components of said electric signals related by a given factor to the frequency components of said audible signals;

variable delay line means having an input and an output, said input coupled to said means for deriving said electric signals for propagating representations of said electric signals to said output with controllable time delay;

means for controlling said delay line means for periodic linear variation of said time delay between predetermined delay values; and

means coupled to said output of said delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to unidirectional variation of said time delay for producing output signals reproducible as an audible representation of said electric signals having frequency components altered by substantially said factor to approximate the frequency components of said audible signals; and

in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line is returned to an initial predetermined delay value and further including;

second delay line means coupled to said means for deriving said electric signals; and

means for interrupting signals from the output of said variable delay line means and substituting signals from the output of said second delay line means during said reset intervals to produce said output signals reproducible as said audible representation.

12. Apparatus according to claim 11 in which said second delay line means include a variable delay line and including means for controlling said second delay line means for periodic linear variation of said time delay between predetermined delay values, said variation of said second delay line means occurring during said reset intervals for the first recited said delay line means.

13. A processor for electric signals representing coded audible signals such as speech or the like, said electric signals being analog representations of said audible signals with the frequency components of said electric signals related by a given factor to the frequency components of said audible signals comprising:

first and second variable delay line means coupled to a source of said electric signals for propagating said electric signals therein with controllable time delay;

means for controlling said first and second delay line means for periodic linear variation of said time delay between predetermined delay values, said means for controlling said first and second delay line means providing periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay lines are returned to an initial predetermined delay value, said reset intervals for each said delay line means occurring within the period of the unidirectional delay variation of the other said delay line means; and

means coupled to the outputs of said first and second delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to unidirectional variation of said delay for producing an audible representation of said electric signals having frequency components altered by substantially said factor to approximate the frequency components of said audible signals.

14. Apparatus according to claim 13 in which said first and second delay line means vary between the same said predetermined delay values alternately with substantially equal periods of said linear variation.

15. Apparatus according to claim 14 in which said reset intervals are substantialLy shorter than the periods of said linear variation and occur for each said delay line means approximately at the mid-point of said linear variation for the other said delay line means and including:

separate audio reproducer means coupled to the respective outputs of said first and second delay line means for producing simultaneously separate versions of said audible representation from each said reproducer means.

16. Apparatus according to claim 11 and including:

input high pass filter means having adjustable low frequency cutoff interposed between said means for deriving said electric signals and said input of said variable delay line means;

means for adjusting the effective rate of said periodic linear variation to adjust said factor by which frequencies propagated through said delay line are altered; and

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation.

17. Apparatus according to claim 16 in which said second delay line means is also a variable delay line and including means for controlling said second delay line means for periodic linear variation of said time delay between predetermined delay values, said variation of said second delay line means occurring during said reset intervals for the first recited said delay line means.

18. A processor for electric signals representing coded audible signals such as speech or the like, said electric signals being analog representations of said audible signals with the frequency components of said electric signals related by a given factor to the frequency components of said audible signals comprising:

first and second variable delay line means coupled to a source of said electric signals for propagating said electric signals therein with controllable time delay;

input high pass filter means having adjustable low frequency cutoff interposed between said source and the input of said variable delay line means;

means for controlling said first and second delay line means for periodic linear variation of said time delay between predetermined delay values, said means for controlling said first and second delay line means providing periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay lines are returned to an initial predetermined delay value, said reset intervals for each said delay line means occurring within the period of the unidirectional delay variation of the other said delay line means;

means for adjusting the effective rate of said periodic linear variation to adjust the factor by which frequencies propagated through said delay line are altered;

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation; and

, means coupled to the outputs of said first and second delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to unidirectional variation of said delay for producing an audible representation of said electric signals having frequency components altered by substantially said given factor to approximate the frequency components of said audible signals.

19. Apparatus according to claim 18 in which said first and second delay line means vary between the same said predetermined delay values alternately with substantially equal periods of said linear variation.

20. Apparatus according to claim 19 in which said reset intervals are substantially shorter than the periods of said linear variation and occur for each said delay linE means approximately at the mid-point of said linear variation for the other said delay line means and including:

separate audio reproducer means coupled to the respective outputs of said first and second delay line means for producing simultaneously separate versions of said audible representation from each said reproducer means.

21. Apparatus according to claim 11 in which said second delay line means is a fixed delay line the input of which is coupled to an output of said variable delay line means.

22. Apparatus according to claim 21 and including:

input high pass filter means having adjustable low frequency cutoff interposed between said source and the input of said variable delay line means;

means for adjusting the effective rate of said periodic linear variation to adjust said factor by which frequencies propagated through said delay line are altered; and

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation.

23. A processor for recordings representing coded audible signals such as speech or the like comprising:

playback means operable to reproduce said recording at a rate faster by a given factor than the recording rate thereby producing electric signals which are the time compressed analog of said audible signals with frequency components increased by said factor;

variable delay line means coupled to said playback means for propagating said electric signals therein with controllable time delay;

means for controlling said delay line means for periodic linear increase of said time delay between predetermined delay values; and

, means coupled to the output of said delay line means and responsive subtantially only to signals propagating through said delay line means which have been subject to said increase of said time delay for producing an audible representation of said electrical signals having frequency components reduced substantially by said factor to approximate the frequency components of said audible signals.

24. Apparatus according to claim 23 and including input high pass filter means, said filter means substantially eliminating components for said electrical signals from propagating through said delay line means which are below a frequency approximately equal to said factor times the reciprocal of the period of said linear variation.

25. Apparatus according to claim 24 and including band pass output filter means limiting said output representation to a predetermined audio bandwidth.

26. Apparatus according to claim 23 and including:

input high pass filter means having adjustable low frequency cutoff interposed between said playback means and the input of said variable delay line means;

means for adjusting the effective rate of said periodic linear variation to adjust said factor by which frequencies propagated through said delay line are altered; and

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation.

27. Apparatus according to claim 26 in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line is returned to an initial predetermined delay value and including means for blanking output signals from said output of said delay line means to substantially zero amplitude during said reset intervals.

28. Apparatus according to claim 27 in which said means for blanking includes means for gradually restoring the amplitude of said output to full amplitude aFter said reset intervals.

29. Apparatus according to claim 2 in which said means for blanking includes means responsive to the level of said output signals being zero at the beginning of said reset interval to initiate said blanking and means responsive to the level of said output signals being zero at the end of said reset interval to terminate said blanking.

30. Apparatus according to claim 29 and including means for introducing an audio signal segment into said output signals and said audible representation of said electric signals during said reset interval.

31. Apparatus according to claim 23 in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line is returned to an initial predetermined delay value and including:

second delay line means coupled to a source of said electric signals; and

means for interrupting signals from the output of said variable delay line means and substituting signals from the output of said second delay line means during said reset intervals to produce said audible representation.

32. Apparatus according to claim 31 in which said second delay line means includes a variable delay line and including means for controlling said second delay line means for periodic linear variation of said time delay between predetermined delay values, said variation of said second delay line means occurring during said reset intervals for the first recited said delay line means.

33. A processor for recordings representing coded audible signals such as speech or the like comprising:

playback means operable to reproduce said recording at a rate faster by a given factor than the recording rate thereby producing electric signals which are the time compressed analog of said audible signals with frequency components increased by said factor;

first and second variable delay line means coupled to said playback means for propagating said electric signals therein with controllable time delay;

means for controlling said first and second delay line means for periodic linear variation of said time delay between predetermined delay values, said means for controlling said first and second delay line means providing periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay lines are returned to an initial predetermined delay value, said reset intervals for each said delay line means occurring within the period of the unidirectional delay variation of the other said delay line means; and

means coupled to the outputs of said first and second delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to unidirectional variation of said delay for producing an audible representation of said electric signals having frequency components reduced by substantially said factor to approximate the frequency components of said audible signals.

34. Apparatus according to claim 33 in which said first and second delay line means vary between the same said predetermined delay values alternately with substantially equal periods of said linear variation.

35. Apparatus according to claim 34 in which said reset intervals are substantially shorter than the periods of said linear variation and occur for each said delay line means approximately at the mid-point of said linear variation for the other said delay line means and including:

separate audio reproducer means coupled to the respective outputs of said first and second delay line means for producing simultaneously separate versions of said audible representation from each said reproducer means.

36. Apparatus according to claim 31 and including:

input high pass filter means having adjustable low frequency cutoff interposed between said source and the input of said variable delay line means;

means for adjusting the effective rate of said pEriodic linear variation to adjust said factor by which frequencies propagated through said delay line are altered; and

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation.

37. Apparatus according to claim 36 in which said second delay line means is also a variable delay line and including means for controlling said second delay line means for periodic linear variation of said time delay between predetermined delay values, said variation of said second delay line means occurring during said reset intervals for the first recited said delay line.

38. Apparatus according to claim 18 in which said source of said electric signals comprises playback means operable to reproduce a recording at a rate faster by a given factor than the recording rate, thereby producing electric signals which are the time compressed analog of said audible signals with frequency components increased by said given factor.

39. Apparatus according to claim 18 in which said first and second delay line means vary between the same said predetermined delay values alternately with substantially equal periods of said linear variation.

40. Apparatus according to claim 39 in which said reset intervals are substantially shorter than the periods of said linear variation and occur for each said delay line means approximately at the mid-point of said linear variation for the other said delay line means and including:

separate audio reproducer means coupled to the respective outputs of said first and second delay line means for producing simultaneously separate versions of said audible representation from each said reproducer means.

41. Apparatus according to claim 40 in which said second delay line means is a fixed delay line the input of which is coupled to an output of said variable delay line means.

42. Apparatus according to claim 41 and including:

input high pass filter means having adjustable low frequency cutoff interposed between said source and the input of said variable delay line means;

means for adjusting the effective rate of said periodic linear variations to adjust said factor by which frequencies propagated through said delay line are altered; and

means coupling said cutoff adjusting means and said effective rate adjusting means for related variation to eliminate low frequency components which would otherwise produce frequency components in said delay line means below an audio low frequency limit related to said factor and the period of said variation.

43. A processor for recordings representing coded audible signals such as speech or the like comprising:

playback means operable to reproduce said recording at a rate slower by a given factor than the recording rate thereby producing electric signals which are the time expanded analog of said audible signals with frequency components decreased by said factor;

variable delay line means coupled to said playback means for propagating said electric signals therein with controllable time delay;

means for controlling said delay line means for periodic linear decrease of said time delay between predetermined delay values; and

means coupled to the output of said delay line means and responsive substantially only to signals propagating through said delay line means which have been subject to said decrease of said time delay for producing an audible representation of said electrical signals having frequency components increased substantially by said factor to approximate the frequency components of said audible signals.

44. Apparatus according to claim 43 in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line Is returned to an initial predetermined delay value and including:

second delay line means coupled to a source of said electric signals; and

means for interrupting signals from the output of said variable delay line means and substituting signals from the output of said second delay line means during said reset intervals to produce said audible representation.

45. Apparatus according to claim 44 in which said second delay line means include a variable delay line and including means for controlling said second delay line means for periodic linear variation of said time delay between predetermined delay values, said variation of said second delay line means occurring during said reset intervals for the first recited said delay line means.

46. Apparatus according to claim 44 in which said second delay line means is a fixed delay line the input of which is coupled to an output of said variable delay line means.

47. Apparatus according to claim 1 in which said delay line means is controlled such that:

the time delay difference between said delay values is d X T where d 2 c-1/c+1, c is said factor and T is said period; and

the period of said variation is greater than the period of the lowest input frequency component to be processed through said line divided by said factor.

48. Apparatus according to claim 1 in which:

said factor is a number greater than one for time compression and less than one for time expansion;

the period of said variation is greater than the period of the lowest frequency component of said electric signals appearing at said output of said delay line; and

said unidirectional variation of said delay is given by 2 (c-1/c+1)t where t is the time and c is said factor.

49. A processor according to claim 1 in which said variable delay line means is an analog shift register and said means for controlling said delay line means is a variable frequency clock pulse generator having a frequency that periodically varies inversely with time.

50. A processor according to claim 11 in which both of said delay line means are analog shift registers each having a variable frequency clock pulse generator.

51. Apparatus according to claim 1 in which said variable delay line means is a parallel r-word-n-stage shift register and including input A/D means for converting said electric signals into a succession of r-bit-digital words;

output D/A means for converting the digital word from the n-th stage into an analog signal and variable frequency clock signal means for transferring the r-bit words from stage to stage through said n stages to effect linear variation of time delay for said signal.

52. Apparatus according to claim 1 in which said variable delay line means comprises input A/D converter means, serializer means to produce a digital word sequence, a serial digital shift register, parallelizer means to produce a parallel digital word and a D/A converter means;

said control means comprising a variable frequency clock generator for said shift register.

53. Apparatus according to claim 1 in which said delay line means comprises an analog storage matrix and including write control means for entering said electric signals into said matrix at a first predetermined clock rate;

and read control means for reading said electric signals from said matrix at a different second predetermined rate.

54. Apparatus according to claim 1 in which said variable delay line means is a digital storage matrix having A/D input means and D/A output means;

and means for writing digital information into storage in said matrix at one rate and reading stored information out of said matrix at another rate.

55. The method of processing random speech signals to convey information intelligibly to a human listener at a rate different than the normal speaking equivalent for said information and without obJectionable alteration of the frequency components of said equivalent as reproduced for the listener comprising the steps of:

developing a full speech signal train of said information with the elapsed time for said signal train altered into a time interval differing by a predetermined factor from that of the normal speaking equivalent for said signal train thereby changing by said factor the frequency of the spectral components in said signal train relative to said equivalent;

processing said signal train by a linear periodic time delay function to alter a regular succession of predetermined length segments of said signal train into segments approximating a continuous signal with the frequency components in said continuous signal altered by said factor relative to said components in said signal train to approximate the components of said normal speaking equivalent; and

reproducing said continuous signal as an intelligible representation of said information content with the elapsed time altered by said factor but with the frequency components unchanged relative to said equivalent.

56. Apparatus according to claim 2 in which said means for blanking includes means responsive to said output signals for initiating and terminating said blanking for zero output signal levels and for signal excursion adjacent said zero levels in the same direction.

57. Apparatus according to claim 43, in which said means for controlling said delay line means provides periods of linearly changing unidirectional delay variation alternating with reset intervals wherein said delay line is returned to an initial predetermined delay value and including means for blanking output signals from said output of said delay line means to substantially zero amplitude during said reset intervals.

58. A processor for electric signals representing coded audible signals such as speech or the like, said electric signals being analog representations of said audible signals with the frequency components of said electric signals related by a given factor to the frequency components of said audible signals comprising:

two similar delay lines coupled to a source of said electric signals for propagating said electric signals between the input and output terminals thereof with controllable frequency transformation;

means for controlling said delay lines alternately for periodic propagation of said electric signals to produce predetermined frequency transformation of signals emerging at the outputs of said delay lines; and

means coupled to said outputs of both said delay line means and responsive substantially only to signals propagating through said delay lines which have been subject to said predetermined frequency transformation for producing an audible representation of said electric signals having frequency components altered by substantially said factor to approximate the frequency components of said audible signals.

59. Apparatus according to claim 58 in which said two delay lines are analog shift registers.

60. Apparatus according to claim 58 in which said analog shift registers are controlled alternately by a clock frequency periodically varied between predetermined limits.

61. The method of processing random speech signals to convey information intelligibly to a human listener at a rate different than the normal speaking equivalent for said information and without objectionable alteration of the frequency components of said equivalent as reproduced for the listener comprising the steps of:

developing a full speech signal train of said information with the elapsed time for said signal train altered into a time interval differing by a predetermined factor from that of the normal speaking equivalent for said signal train thereby changing by said factor the frequency of the spectral components in said signal train relative to said equivalent;

propagating said signal train through a storage channel within which it is subject to a periodic frequency transformAtion function to alter a regular succession of predetermined length input segments of said signal train into output segments approximating a continuous signal with the frequency components in said continuous signal altered by the inverse of said factor relative to said components in said signal train to approximate the components of said normal speaking equivalent; and

reproducing said continuous signal as an intelligible audible representation of the information content of said signal train but with the frequency components unchanged relative to said equivalent.

62. The method according to claim 61 in which said storage channel comprises analog shift register means controlled by a clock frequency periodically varied between predetermined frequency values.

63. The method according to claim 62 in which said input segments are propagated alternately through separate analog shift registers for frequency transformation.

64. Apparatus according to claim 48 in which said delay line means comprises analog shift register means and said periodic variation of said time delay is obtained by controlling the clock frequency for said shift register means to provide said unidirectional variation of said delay to be:

N (p-1/p) ( 1/ft -(1/fo ) 2 (c-1/c+1) t where ft is the clock frequency at time t, N is the number of stages of phase p and fo is the initial clock frequency.

65. In a processor for electric signals such as those representing the coded audible sounds of speech or the like, said electric signals being analog representations of said audible sounds with the frequency components of said electric signals related by a given factor to the frequency components of said audible sounds, the improvement comprising:

controllable delay means having an input and an output, said input coupled to a source of said electric signals for passing signals from said source into said delay means, and said delay means passing signals therein to said output with controllable time delay;

means for controlling said delay means with repetitive variation of said controllable time delay between predetermined delay values the period of said variation being greater than the period of the lowest frequency component of said electric signals at said output of said delay means thereby progressively delaying signals during each period of said repetitive variation as they pass through said delay means to obtain a predetermined frequency transformation of said electric signals as determined by the relation;