AUDIO-DIGITAL RECORDING SYSTEM

• US 3,786,201 A
• Filed: 02/04/1972
• Issued: 01/15/1974
• Est. Priority Date: 02/04/1972
• Status: Expired due to Term

• Current Assignee: Gleb Tschapek, John P. Myers
• Original Assignee: Gleb Tschapek, John P. Myers
• Inventors: Myers, John P., Tschapek, Gleb
• Primary Examiner(s): Canney, Vincent P.
• Assistant Examiner(s): Eddleman, Alfred H.
• Application Number:
  US05/223,532
• Time in Patent Office: 711 Days
• Field of Search: 179/1.2R,1.2K 340/174.1G,174.1K,174.1A,174.1B,172.5,347SH,347AD,347DA 178/DIG.3,6.6A
• US Class Current: 360/32
• CPC Class Codes: G11B 20/10527 Audio or video recording; Data buffering arrangements G11B20/12 - G11B20/18 take precedence
• CPC Class Codes: G11B 20/20 for correction of skew for multitrack recording

Abstract

A system for converting an input analog signal, such as an audio signal or signal representative of sound into a digital form for storing in digital form and for reconstructing the input analog signal from the digital form is disclosed. The system includes sampling means for converting the input audio signal into a binary format which includes ranging bits and adjusted magnitude bits. This permits the recording in digital form of audio signals of a wide dynamic range with a reduced number of bits. Additionally, the disclosed encoding method for encoding digital words prior to recording reduces pulse crowding on magnetic tape and achieves higher bit packing densities. The system may be used with existing professional audio tape drives with tape speeds of approximately 30 ips or less.

Claims

1. A system for preparing an analog signal for recording or transmission in digital form comprising:

sample and hold means, for sampling said analog signal, said means having a variable gain;

control and timing means for sensing said analog signal and for providing a control signal for varying the gain of said sample and hold means as a function of the magnitude of said analog signal and for providing timing information for said sample and hold means, said control means being coupled to said sample and hold means;

an analog-to-digital converter for converting the output signals of said sample and hold means into digital signals;

whereby the output of said analog-to-digital converter and signals representative of the gain of said sample and hold means may be recorded or transmitted.

2. The system defined in claim 1 wherein said sample and hold means comprises two sample and hold circuits coupled in series, each of which includes at least one amplifier, the gain and sampling rate of which is varied by said control means.

3. The system defined in claim 1 including means for reproducing the analog signal from the recorded or transmitted reproduce signal, said reproducing means including:

a delay differentiator network for sensing the input reproduce signal and for providing an output signal representative of the differentiator of the input reproduce signal;

a hysteresis network for producing a control signal based on peak and amplitude ratios of the input reproduce signal and for providing an output signal representative of said peaks;

a combining means coupled to said delay differentiator network and hysteresis network for combining the outputs of said networks in accordance with a predetermined algorithm.

4. The system defined in claim 1 wherein the output of said analog-to-digital converter is alternately coupled to at least a first and second buffer such that the digital signal representative of the input analog signal may be recorded or transmitted as two separate digital signals.

5. The system defined in claim 4 including reproduce means for converting the recorded or transmitted digital signal into analog form, said reproduce means including at least two pairs of digital buffers, each pair of which may be asynchronously clocked, so that when one of said separate digital signals loaded into one pair of buffers and the other separate digital signal loaded into the other pair of said buffers, the buffers may be asynchronously clocked so that the two separate digital signals may be converted into a single digital signal and any time misalignment problems between the two separate digital signals such as those caused by magnetic tape skew may be eliminated.

6. The system defined in claim 4 wherein time delay means for providing a time delay is coupled to said sample and hold means such that said input analog signal is delayed before reaching the sample and hold means.

7. The system defined in claim 6 including at least two buffers for receiving digital signals, coupled to said analog-to-digital converter, such that signals from said analog-to-digital converter are alternately applied to said first buffer and then to said second buffer, so that the output of said analog-to-digital converter may be recorded or transmittEd on two separate tracks.

8. The system defined in claim 6 wherein the time delay of said delay means is approximately equal to the time required for said control means to sense the input analog signal and to vary the gain of said sample and hold means and the aperture time of the first sample and hold circuit.

9. The system defined in claim 8 wherein the variable gain of said sample and hold means comprise a plurality of predetermined fixed gains.

10. The system defined in claim 9 including two means for encoding digital signals wherein the output from said analog-to-digital converter is alternately applied to the first means for encoding and then to the second means for encoding, such that the digital signals representative of the input analog signal may be separated into two separate tracks.

11. A system for converting an input analog signal to digital form comprising:

a comparator circuit for sensing the input analog signal and for providing an output signal which indicates the range of the magnitude of the input signal;

a sample and hold means for sampling said input analog signal, said means having a variable gain;

encoding means for varying the gain of said sample and hold means in accordance with predetermined logic and as a function of said output signal of said comparator circuit, said encoding means being coupled to said comparator circuit and said sample and hold means;

timing means for providing a sampling rate coupled to said encoding means such that said gain of said sample and hold means is controlled through said encoding means by at least one signal which controls both said sampling rate and said gain;

an analog-to-digital converter, for converting the samples from said sample and hold means to digital form, coupled to said sample and hold means;

whereby the digital signals from said analog-to-digital converter and a signal representative of the gain of said sample and hold means may be recorded or transmitted.

12. The system defined in claim 11 including means for reproducing the analog signal from the recorded or transmitted reproduce signal, said reproducing means including:

a delay differentiator network for sensing the input reproduce signal and for providing an output signal representative of the differentiator of the input reproduce signal;

a hysteresis network for producing a control signal based on peak amplitude ratios of the input reproduce signal and for providing an output signal representative of said peaks;

a combining means coupled to said delay differentiator network and hysteresis network for combining the outputs of said networks in accordance with a predetermined algorithm.

13. The system defined in claim 11 including means for encoding the output of said analog-to-digital converter and a digital signal representative of the gain of the sample and hold means for each sample of said input signal prior to the recording of said digital signals.

14. The system defined in claim 13 wherein said encoding means implements the following algorithm:

a. if a clocking signal having a frequency of twice the bit frequency of the data comprising the output of said converter and said digital signal representative of said gain, is in a first state and said data is in said first state, an encoded signal in one state will result. b. if either the data or clocking signal is in a first state and the other of said data or clocking signal is in a second state, an encoded signal in the other state will result.

15. The system defined in claim 13 including reproduce means for converting the recorded or transmitted digital signal into analog form, said reproduce means including at least two pairs of digital buffers, each pair of which may be asynchronously clocked, so that when one of said separate digital signals loaded into one pair of buffers and the other separate digital signal loaded into the other pair of said buffers, the buffers may be asynchronously clocked so that the two seParate digital signals may be converted into a single digital signal and any time misalignment problems between the two separate digital signals such as those caused by magnetic tape skew may be eliminated.

16. The system defined in claim 11 wherein said sample and hold means comprises two sample and hold circuits coupled in series, each of which includes at least one amplifier the gain and sampling rate of which are controlled by said encoding means.

17. The system defined in claim 16 wherein the output from said encoding means which controls the gain and sampling rate of said sample and hold means includes a plurality of binary signals.

18. The system defined in claim 17 wherein time delay means for providing a time delay is coupled to said sample and hold means such that said input analog signal is delayed before reaching the sample and hold means.

19. The system defined in claim 18 wherein the time delay of said delay means is approximately equal to the time required for said comparator circuit and said encoding means to sense the input analog signal and to vary the gain of said sample and hold means and the aperture time of the first of said two sample and hold circuits.

20. The system defined in claim 17 wherein the variable gain of said sample and hold means comprise a plurality of predetermined fixed gains.

21. The system defined in claim 20 wherein the input analog signal is an audio signal, said sample and hold means has four predetermined gains and wherein said encoding means provides digital signals representative of said predetermined gains of said sample and hold means as said gains are varied by said encoding means.

22. A system for recording an audio input signal in digital form comprising:

a sample and hold means for sampling said input signal and for providing output samples of said input signal, said sample and hold means having a plurality of predetermined gains;

control means for sensing the input signal and for providing a control signal for selecting said predetermined gains of said sample and hold means as a function of the amplitude of said input signal;

timing means for controlling the sampling rate of said sample and hold means coupled to said control means such that said control signal controls said sampling rate of said sample and hold means;

an analog-to-digital converter for converting the output samples of said sample and hold means into digital signals;

recording means for recording the output digital signals from said analog-to-digital converter;

whereby the audio input signal is recorded in digital form.

23. The system defined in claim 22 including means for reproducing the analog signal from the recorded or transmitted reproduce signal, said reproducing means including:

a delay differentiator network for sensing the input reproduce signal and for providing an output signal representative of the differentiator of the input reproduce signal;

a hysteresis network for producing a control signal based on peak amplitude ratios of the input reproduce signal and for providing an output signal representative of said peaks;

a combining means coupled to said delay differentiator network and hysteresis network for combining the outputs of said networks in accordance with a predetermined algorithm.

24. The system defined in claim 22 wherein said control means includes means for generating digital signals representative of the selected predetermined gain of said sample and hold means and wherein said signals are coupled to said recording means for recording along with the output of said analog-to-digital converter.

25. The system defined in claim 24 wherein the output of said analog-to-digital converter is alternately coupled to a first buffer means and then to a second buffer means so that the digital signal representative of said input audio signal may be recorded on two tracks on said recording means.

26. The system defined in claim 25 wherein said recording means is a magnetic tape recorder.

27. The system defined in claim 24 wherein said sample and hold means comprises two sample and hold circuits, coupled in series, each of which includes at least one amplifier, the gain of which is adjusted by said control means.

28. The system defined in claim 27 wherein the output of said analog-to-digital converter is alternately coupled to a first buffer means and then to a second buffer means so that the digital signal representative of said input audio signal may be recorded on two tracks on said recording means.

29. The system defined in claim 27 wherein time delay means for providing a time delay is coupled to said sample and hold means such that said input audio signal is delayed before reaching said sample and hold means.

30. The system defined in claim 29 wherein the time delay of said delay means is approximately equal to the time required by said control means to sense said input audio signal and to select one of said plurality of predetermined gains of said sample and hold means and the aperture time of said first circuit of said sample and hold means.

31. The system defined in claim 30 wherein said recording means is a magnetic tape recorder.

32. A system for converting an input analog signal into a digital signal for recording or transmission and for reconstructing the analog signal from the transmitted or recorded digital signal comprising:

a sample and hold means for sampling the input analog signal and for providing periodic output samples of said analog signal, said sample and hold means having a variable gain;

control means for sensing said input signal and for providing a control signal for controlling the gain of said sample and hold means as a function of the amplitude of said input analog signal;

at least one analog-to-digital converter for converting the output samples from said sample and hold means into digital form coupled to said sample and hold means;

at least two buffers for alternately receiving signals from said analog-to-digital converter such that the output from said analog-to-digital converter is separated into at least two separate signal tracks;

at least two encoding means, one coupled to each of said buffer for encoding the digital outputs from said buffers and digital signals representative of the gain of said sample and hold means in accordance with a predetermined algorithm;

at least a pair of decoding means for decoding the digital signals from said encoding means in accordance with a predetermined algorithm, said decoding means coupled to said encoding means through a recording medium or transmission medium;

at least one digital-to-analog converter coupled to said decoding means for converting at least a portion of each digital word into analog form;

at least one amplifier coupled to said digital-to-analog converter for amplifying the signal from said digital-to-analog converter as a function of said digital signals representative of the gain of said sample and hold means;

whereby the output of said amplifier means is a reconstructed input analog signal.