US4803727A
Expired / Lapsed
US
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Transmission system
Assignee: British Telecommunications PLC
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Filing: 1987-11-24
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Granted: 1989-02-07
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Expires: 2007-11-24
Abstract
Abstract A stereo coding system is described in which 7 kHZ bandwidth sum (L+R) and difference (L-R) signals are converted to digital form (11 and 12). The difference signal is then bandlimited (13) to 2 kHZ and downsampled (14) to 4K samples/sec prior to being encoded (16), and the sum signal is encoded (15); both are then multiplexed together (17) prior to transmission. After reception, the signal is demultiplexed (19) and the difference signal is decoded (20) upsampled (21) to its original bit rate and filtered to prevent aliasing (22), and the sum signal is delayed in a digital buffer (28) and decoded (24) prior to both being converted back to analogue form (23 and 25). The delay introduced by the digital buffer (28) equalizes the excess delay introduced into the difference signal.
Inventors
- 👤 Christopher E. Holt
- 👤 John M. Rollett
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 19:29
CPC Classifications
H; H04; H04H; H04H20/00; H04H20/86; H04H20/88; H04B; H04B14/00; H04B14/02; H04B14/04; H04B14/046; H04S; H04S1/00; H04S1/007
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
132 words
A transmission system for audio signals in which at a transmitter: a monphonic signal and a difference signal are derived from multiple input signals, a digital version of the difference signal is bandlimited to a predetermined bandwidth smaller than that of the monophonic signal, the sampling rate of the digital bandlimited difference signal is reduced; and the monophonic and resulting difference signals are transmitted to a receiver; and in which at a receiver: upon reception, the sampling rate of the digital difference signal is increased, frequencies above the predetermined bandwidth in the difference signal are attenuated, and left and right output signals are derived from the monophonic and resultant difference signals; and in which, either at the transmitter or receiver, compensation for differential delays in the monophonic and difference signals is introduced.
Claim 2
Dependent Claim
132 words
A transmission system for audio signals in which at a transmitter: a monphonic signal and a difference signal are derived from multiple input signals, a digital version of the difference signal is bandlimited to a predetermined bandwidth smaller than that of the monophonic signal, the sampling rate of the digital bandlimited difference signal is reduced; and the monophonic and resulting difference signals are transmitted to a receiver; and in which at a receiver: upon reception, the sampling rate of the digital difference signal is increased, frequencies above the predetermined bandwidth in the difference signal are attenuated, and left and right output signals are derived from the monophonic and resultant difference signals; and in which, either at the transmitter or receiver, compensation for differential delays in the monophonic and difference signals is introduced.
Claim 3
Dependent Claim
66 words
A transmitter for use in a transmission system according to claim 1, comprising: a means for receiving said multiple input signals, and for forming said monophonic signal and said digital difference signal therefrom; a digital filter for bandlimiting the digital difference signal to a predetermined bandwidth smaller than that of the monophonic signal; and a downsampler for reducing the sampling rate of the filtered difference signal.
Claim 4
Dependent Claim
20 words
A transmitter according to claim 2, further comprising compensating means for compensating differential delays in the monophonic and difference signals.
Claim 5
Dependent Claim
35 words
A transmitter according to claim 3, further comprising analogue-to-digital converter means for providing the monophonic signal in digital form, wherein the compensating means is a digital delay for introducing a delay into the monophonic signal.
Claim 6
Dependent Claim
25 words
A transmitter according to claim 4 further comprising two identical analogue filters for filtering the monophonic and difference signals prior to conversion to digital form.
Claim 7
Dependent Claim
23 words
A transmitter according to claim 4 or 5 wherein both the digitial monophonic and difference signals are provided at the same sampling rate.
Claim 8
Dependent Claim
22 words
A transmitter according to any one of claims 2, 3, 4 or 5 wherein the said predetermined bandwidth is substantially 2 kHz.
Claim 9
Dependent Claim
66 words
A transmitter according to any one of claims 2, 3, 4 or 5 further comprising means for determining which of the multiple input signals is currently the dominant source of sound and means for generating a data signal carrying information about the adjustment of the power ratio of the left and right output signals to be performed in the frequency range above said predetermined maximum bandwidth.
Claim 10
Dependent Claim
87 words
A receiver for use in a transmission system according to claim 1, comprising: receiving means for receiving monophonic signals, and for receiving digital difference signals having a predetermined maximum bandwidth less than that of the monophonic signals; an upsampler for increasing the sampling rate of the difference signals; a digital filter for attenuating frequencies above the said predetermined maximum bandwidth in the upsampled difference signal; and digital-to-analogue conversion and mixing means for forming analogue left and right output signals from the monophonic and filtered upsampled difference signals.
Claim 11
Dependent Claim
19 words
A receiver according to claim 9 comprising compensating means for compensating differential delays in the monophonic and difference signals.
Claim 12
Dependent Claim
32 words
A receiver according to claim 10 wherein the monophonic signal is also received in digital form and the compensating means is a digital delay for introducing a delay into the monophonic signal.
Claim 13
Dependent Claim
20 words
A receiver according to claim 11 further comprising two identical analogue filters for filtering the left and right output signals.
Claim 14
Dependent Claim
21 words
A receiver according to any one of claims 9 to 12 wherein the said predetermined maximum bandwidth is substantially 2 kHz.
Claim 15
Dependent Claim
23 words
A receiver according to claim 11 or 12 wherein the upsampled difference signal and the received monophonic signal have the same sampling rate.
Claim 16
Dependent Claim
59 words
A receiver according to any one of claims 9, 10, 11 or 12 also comprising means for adjusting the power ratio of the left and right output signals in the frequency range above said predetermined maximum bandwidth in accordance with the relative power of the left and right output signals in the frequency range below said predetermined maximum bandwidth.
Claim 17
Dependent Claim
47 words
A receiver according to any one of claims 9, 10, 11 or 12 also comprising means for adjusting the power ratio of the left and right output signals in the frequency range above said predetermined maximum bandwidth in accordance with information carried in a received data signal.
Claim 18
Dependent Claim
40 words
A transmission apparatus for stereophonic audio signals comprising: means for forming monophonic and difference signals from left and right input signals; means for bandlimiting the difference signal to substantially 2 kHz; and means for transmitting the monophonic and difference signals.
Claim 19
Dependent Claim
40 words
A transmission apparatus for stereophonic audio signals comprising: means for forming monophonic and difference signals from left and right input signals; means for bandlimiting the difference signal to substantially 2 kHz; and means for transmitting the monophonic and difference signals.
References Cited (Backward Citations)
US3046329A
Cited
GB540185A
Cited
GB945546A
Cited
GB970051A
Cited
US3240878A
Cited
US3976842A
Cited
US4246615A
Cited
US4181822A
Cited
US4638506A
Cited
US4309722A
Cited
US4406001A
Cited
US4534054A
Cited
US4388654A
Cited
US4538234A
Cited
US4509185A
Cited
US4575773A
Cited
US4682248A
Cited
US4608456A
Cited
WO1985000686A1
Cited
EP0145332A2
Cited
US4692818A
Cited
US4723285A
Cited
US4630298A
Cited
US4712240A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-02-07 | 1992-08-08 | 1993-02-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-02-07 | 1996-08-08 | 1997-02-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-02-07 | 2000-08-08 | 2001-02-07 | $7700.00 | Window Closed / Lapsed |