System for carrying transparent digital data within an audio signal

• US 5,612,943 A
• Filed: 07/05/1994
• Issued: 03/18/1997
• Est. Priority Date: 07/05/1994
• Status: Expired due to Fees

• Current Assignee: Hustig, Charles H., Moses, Robert W., Norman Durkee
• Original Assignee: Hustig, Charles H., Moses, Robert W., Norman Durkee
• Inventors: Moses, Robert W., Hustig, Charles H., Durkee, Norman
• Primary Examiner(s): Edun, Muhammad N.
• Application Number:
  US08/270,252
• Time in Patent Office: 987 Days
• Field of Search: 369/124, 369/47, 369/48, 369/49, 369/50, 369/54, 369/58, 369/59, 360/29, 360/48, 360/32
• US Class Current: 369/124.09
• CPC Class Codes: G10H 2240/311 MIDI transmission G10H2240/056 takes precedence
• CPC Class Codes: G11B 20/02 Analogue recording or reproducing
• CPC Class Codes: G11B 20/10527 Audio or video recording; Data buffering arrangements G11B20/12 - G11B20/18 take precedence

Abstract

A signal processing system comprises inputs for an analog audio signal and a digital data signal. The digital data signal is modulated to an analog data signal in an inaudible frequency band. Filters are used to ensure that the audio signal is restricted to audible frequencies and that the analog data signal is restricted to inaudible frequencies. The two analog signals are then combined into a composite analog signal. The composite signal is stored on a medium such as a compact disc. Filters are used to extract and separate the two analog signals from the composite signal stored on the medium. The analog data signal is demodulated to retrieve the original digital data signal.

Claims

1. A system for combining an unmodulated first analog signal and a digital signal, said system comprising:

means for modulating said digital signal to a second analog signal different from said first analog signal;

a first filter for attenuating, in a first frequency band, the amplitude of said second analog signal;

a second filter for attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

means for combining said first and second filtered analog signals to form a single composite analog signal,

a third filter for attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

a fourth filter for attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal;

means for demodulating said second analog signal to said digital signal; and

wherein;

said first band consists of frequencies below a -3 dB cutoff frequency,

said second band consists of frequencies above said cutoff frequency,

said first signal consists essentially of frequencies contained within said first band, and

said second signal consists essentially of frequencies contained within said second band.

2. The system of claim 1, wherein said cutoff frequency is 18 kHz.

3. A system for combining an unmodulated first analog signal and a digital signal, said system comprising:

means for modulating said digital signal to a second analog signal different from said first analog signal;

a first filter for attenuating, in a first frequency band, the amplitude of said second analog signal;

a second filter for attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

means for combining said first and second filtered analog signals to form a single composite analog signal,

a third filter for attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

a fourth filter for attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal; and

means for demodulating said second analog signal to said digital signal; and

wherein said modulator and said demodulator utilize phase shift keying technology.

4. A System for combining an unmodulated first analog signal and a digital signal, said system comprising:

means for modulating said digital signal to a second analog signal different from said first analog signal;

a first filter for attenuating in a first frequency band, the amplitude of said second analog signal;

a second filter for attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

means for combining said first and second filtered analog signals to form a single composite analog signal,

a third filter for attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

a fourth filter for attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal; and

means for demodulating said second analog signal to said digital signal; and

wherein said modulator and said demodulator utilize quadrature phase shift keying technology.

5. A system for combining an unmodulated first analog signal and a digital signal, said system comprising:

means for modulating said digital signal to a second analog signal different from said first analog signal;

a first filter for attenuating, in a first frequency band, the amplitude of said second analog signal;

a second filter for attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

means for combining said first and second filtered analog signals to form a single composite analog signal,

a third filter for attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

a fourth filter for attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal; and

means for demodulating said second analog signal to said digital signal; and

wherein said modulator and said demodulator utilize frequency shift keying technology.

6. A method for combining an unmodulated first analog signal and a digital signal, said process comprising:

modulating said digital signal to a second analog signal different from said first analog signal;

attenuating, in a first frequency band, the amplitude of said second analog signal;

attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

combining said first and second analog signals to form a single composite analog signal;

attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal;

demodulating said second analog signal to said digital signal; and

wherein;

said first band consists of frequencies below a -3 dB cutoff frequency,

said second band consists of frequencies above said cutoff frequency,

said first signal consists essentially of frequencies contained within said first band, and

said second signal consists essentially of frequencies contained within said second band.

7. The method of claim 6, wherein said cutoff frequency is 18 kHz.

8. A method for combining an unmodulated first analog signal and a digital signal, said process comprising:

modulating said digital signal to a second analog signal different from said first analog signal;

attenuating, in a first frequency band, the amplitude of said second analog signal;

attenuating, in a second frequency band, the amplitude of said first analog signals, said first and second bands being nonoverlapping;

combining said first and second analog signals to form a single composite analog signal;

attenuating, in said second frequency bands, the amplitude of said composite signal to extract said first analog signal;

attenuating, in said first frequency bands, the amplitude of said composite signal to extract said second analog signal;

demodulating said second analog signal to said digital signal; and

wherein the steps of modulating said digital signal, and of demodulating said second analog signal are performed utilizing phase shift keying technology.

9. A method for combining an unmodulated first analog signal and a digital signal, said process comprising:

modulating said digital signal to a second analog signal different from said first analog signal;

attenuating, in a first frequency band, the amplitude of said second analog signal;

attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

combining said first and second analog signals to form a single composite analog signal;

attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal;

demodulating said second analog signal to said digital signal; and

wherein the steps of modulating said digital signal, and of demodulating said second analog signal are performed utilizing quadrature phase shift keying technology.

10. A method for combining an unmodulated first analog signal and a digital signal, said process comprising:

modulating said digital signal to a second analog signal different from said first analog signal;

attenuating, in a first frequency band, the amplitude of said second analog signal;

attenuating, in a second frequency band, the amplitude of said first analog signal, said first and second bands being nonoverlapping;

combining said first and second analog signals to form a single composite analog signal;

attenuating, in said second frequency band, the amplitude of said composite signal to extract said first analog signal;

attenuating, in said first frequency band, the amplitude of said composite signal to extract said second analog signal;

demodulating said second analog signal to said digital signal; and

wherein the steps of modulating said digital signal, and of demodulating said second analog signal are performed utilizing frequency shift keying technology.