System for transferring wide-band sound signals

• US 3,894,190 A
• Filed: 01/30/1974
• Issued: 07/08/1975
• Est. Priority Date: 02/28/1973
• Status: Expired due to Term

• Current Assignee: Nokia Graetz Gesellschaft Mit Beschrankter Haftung
• Original Assignee: Gerhard Gunter Gassmann
• Inventors: Gassmann, Gerhard Gunter
• Primary Examiner(s): Stewart, David L.
• Application Number:
  US05/438,124
• Time in Patent Office: 524 Days
• Field of Search: 179/15.55R,15BM,15BP,15AS,1SA,1SC,1SG
• US Class Current: 704/205
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: H04B 1/667 using a division in frequency subbands for TV signals H04N19/63

Abstract

A system for transmitting wide-band signals over a narrow band by directly transmitting low frequency range signals and transmitting amplitude information of partial upper frequency ranges on pilot frequencies is made compatible with existing receivers by making the pilot frequency signals imperceptible in ordinary receivers through the use of a phenomenon known as the masking effect. This is achieved by positive modulation of the pilot frequencies and attentuation to a level 10 db below the level of the low frequency range. If sequential transmission is used, a low level sync signal is produced that does not exceed the signal-to-noise level in existing receivers and is therefore suppressed. In the receivers of the present invention, the low level sync signal is selectively evaluated for control and synchronization of a clock generator but is suppressed below the signal-to-noise ratio of the output and is therefore made inaudible. The sync signal is further processed to control the gain of a modulated pilot signal amplifier and to automatically switch off the upper frequency range signals in the event of sync signal failure or synchronization failure.

Claims

1. A transmitter for transferring wide-band sound signals over a narrow frequency range, comprising:

means for receiving the sound signals;

means for dividing the received sound signals into a lower frequency range and a plurality of higher frequency ranges;

means for providing amplitude signals corresponding to the amplitudes of the signals in each of the higher frequency ranges;

means for providing at least one pilot frequency signal;

means for positively modulating the pilot frequency signal with the amplitude signals in such a way that on a time average the amplitude of the modulated pilot frequency signal is lowered with respect to the amplitude of the lower frequency range signals by an amount corresponding to the limit of perceptibility; and

means for transferring the signals of the lower frequency range and the modulated pilot frequency signal whereby the lower frequency range signals may be received and reproduced by existing receivers while the pilot frequency signals are inaudible in existing receivers so that the transmitter is compatible with existing systems.

2. A transmitter as described in claim 1, wherein a pilot frequency signal is provided for each higher frequency range and the pilot frequency signals are positively modulated with the amplitude signals so that the modulated pilot frequency signals are transmitted simultaneously.

3. A transmitter as described in claim 1, additionally comprising:

means for sequentially modulating a single pilot frequency signal with the amplitude signals of the higher frequency ranges;

means for providing a sync signal having a level not greater than the noise level of existing receivers and corresponding to the repetition rate of the sequential modulation of the pilot frequency signal; and

means for transferring the sync signal so that in existing receivers the sync signal is suppressed along with the moise and is thereby made inaudible.

4. A transmitter as described in claim 3, wherein the sync signal is a sinusoidal voltage transferred simultaneously with the modulated pilot frequency signal and has a frequency corresponding to 1/2 the repetition frequency of the sequential modulation of the pilot frequency signal.

5. A transmitter as described in claim 3, wherein the sync signal is a trapezoidal voltage containing only odd harmonics and is transferred simultaneously with the modulated pilot frequency signal and has a frequency corresponding to 1/2 the repetition frequency of the seqUential modulation of the pilot frequency signal.

6. A receiver for use in a system having a transmitter of the type that transfers lower frequency range sound signals directly, a pilot frequency signal sequentially modulated by amplitude signals corresponding to the amplitudes of sound signals in a predetermined number N of higher frequency ranges and a sync signal corresponding to the repetition rate of the sequential modulation of the pilot frequency signal, said receiver comprising:

means for receiving and demodulating the modulated pilot frequency signal to provide sequential amplitude signals corresponding to the amplitudes of the signals in the high frequency ranges;

means for providing synthetic signals having frequencies approximately equal to the mid range frequency of each higher frequency range;

means for modulating each synthetic signal with the appropriate amplitude signal;

means for distributing the sequential amplitude signals to the modulating means;

means for receiving and reproducing the modulated synthetic signals and the directly transferred low frequency range sound signals;

means for receiving the sync signal and selectively evaluating the same so that the signal-to-noise ratio of the sync signal corresponds to the signal-to-noise ratio of the lower frequency range; and

means responsive to the selected sync signal for controlling and synchronizing said distributing means to assure proper distribution of the sequential amplitude signals.

7. A receiver as described in claim 6, wherein the means responsive to the selected sync signal comprises a clock generator for providing a clock signal to the distributing means and the means for receiving the sync signal comprises a multiplicative mixer connected to receive the sync signal and a signal corresponding to the clock signal.

8. A receiver as described in claim 6 additionally comprising a variable gain amplifier for amplifying the modulated pilot frequency signal.

9. A receiver as described in claim 8, wherein the amplifier gain is controlled by the sync signal.

10. A receiver as described in claim 6, additionally comprising means for switching off the synthetic signals in the event of a sync signal failure or malfunction.

11. A receiver as described in claim 10, wherein the means for switching off the synthetic signals comprises;

a controllable switch connecting the synthetic signals to the reproducing means; and

means for evaluating the sync signal and for controlling the controllable switch in response to the level of the sync signal.

12. A receiver as described in claim 7, wherein the signal corresponding to the clock signal has a frequency equal to 1/2N times the frequency of the clock signal.

13. A receiver as described in claim 6, wherein the means responsive to the selected sync signal comprises a clock generator for providing a clock signal to the distributing means and the means for receiving the sync signal comprises, first and second frequency dividers connected to receive the clock signal and in response thereto provide signals having a frequency equal to 1/2N times the frequency of the clock signal, the first divider providing a signal in phase with the clock signal and the second divider providing a signal 90* out of phase with the clock signal, first and second multiplicative mixers each connected to receive the sync signal, the first mixer being connected to the first frequency divider for receiving the signal therefrom and the second mixer being connected to the second frequency divider for receiving the signal therefrom, the mixers each providing an output voltage in response to the received signals, and first and second low pass filters connected to receive the voltage output from the first and second multiplicative mixers respectively for providing low frequency outputs the output of the first low pass filter being connected to the clock generator for synchronizing the clock generator, said receivEr additionally comprising means connected to the output of the second low pass filter for switching off the synthetic signals when the output of the low pass filter drops below a predetermined level.

14. A receiver as described in claim 13, additionally comprising a variable gain amplifier for amplifying the modulated pilot frequency signal, said amplifier being connected to the output of the second low pass filter for controlling the gain of the amplifier.

15. A receiver as described in claim 6, wherein the distributing means comprises a plurality of switches and the means responsive to the selected sync signal comprises a clock generator for providing clock pulses and the means for receiving the sync signal comprises:

a shift register connected to said clock generator and responsive to said clock pulses, said shift register having outputs connected to the switches providing signals thereto for successively activating the switches;

a multiplicative mixer connected to receive the sync signal and one of the outputs of said shift register for providing an output voltage in response to the received signals, said clock generator being connected to the multiplicative mixer for receiving the output voltage therefrom whereby the clock generator is synchronized with the sync signal.

16. A receiver as described in claim 6, wherein the distributing means comprises a switch assembly having N switching means and the means responsive to the selected sync signal comprises a clock generator for providing clock pulses and the means for receiving the sync signal comprises:

shift register means connected to said clock generator and responsive to said clock pulses, said shift register means having outputs connected to the switch assembly for providing pulses thereto for sucessive activation of the switching means;

a first frequency halving flip-flop connected to a first output of said shift register for receiving a pulse therefrom;

a second frequency halving flip-flop connected to a second output of said shift register said second output providing a pulse spaced in time N/2 clock pulses from the pulse of the first output, the output of the first flip-flop being connected to the enabling input of the second flip-flop so that the outputs of the flip-flops are always 90* apart;

first and second multiplicative mixers each connected to receive the sync signal, the first mixer being connected to the output of the first flip-flop and the second mixer being connected to the output of the second flip-flop, the mixers each providing an output voltage in response to the received signals, the output of the first multiplicative mixer being connected to the clock generator for synchronizing the clock pulses and the output of the second mixer being connected to means for switching off the synthetic signals in the event of a sync signal failure or malfunction.

17. A system for transferring wide-band sound signals over a narrow frequency range, comprising:

a transmitter including means for receiving the sound signals, means for dividing the received sound signals into a lower frequency range and a plurality of higher frequency ranges, means for providing amplitude signals corresponding to the amplitude of the signals of each of the higher frequency ranges, means for providing at least one pilot frequency signal, means for positively modulating the pilot frequency signal with the amplitude signals in such a way that on a time average the amplitude of the modulated pilot signal is lowered with respect to the amplitude of the lower frequency range signals by an amount corresponding to the limit of perceptibility, and means for transferring the signals of the lowered frequency range and the modulated pilot frequency signal whereby the lower frequency range signals may be received and reproduced by existing receivers while the pilot frequency signal is inaudible in existing receivers; and

a receiver including means for receiving and demodulating the modulated pilot frequency signal to provide amplitude signals corresponding to the amplitudes of the signals in the high frequency range, means for providing synthetic signals having frequencies approximately equal to the mid-range frequency of each higher frequency range, means for modulating each synthetic signal with the appropriate amplitude signal, and means for receiving and reproducing the modulated synthetic signals and the directly transferred low frequency range signals.