Method and device for monitoring an abnormality in digitally transmitted audio signals

Claim 2

A digital transmission system for digitally transmitting an analogue base band audio signal, said digital transmission system comprising: a transmission unit having: a first and second low-pass filter for band limiting a first analogue audio signal into predetermined frequency bands; and a first and second analogue/digital conversion means for respectively converting the outputs of said first and second low-pass filters to n-bit digital data and m-bit digital data respectively, where m is less than n; and a reception unit having: a digital/analogue conversion means for converting said m-bit digital data to an analogue data signal; a third low-pass filter for band limiting said analogue data signal into a predetermined frequency band; a fourth low-pass filter for band limiting a second analogue audio signal obtained by analogue converting said n-bit digital data transmitted from said transmission unit; and a comparison means for comparing the output level of said third low-pass filter with the output level of said fourth low-pass filter.

Claim 3

The digital transmission system of claim 1, wherein said comparison means comprises; a means for calculating the difference between an output level of said third low-pass filter and an output level of said fourth low-pass filter and determining the transmission abnormal if a calculated difference is not less than a predetermined threshold value.

Claim 4

The digital transmission system of claim 1 wherein said transmission unit further comprises: a multiplexing means for multiplexing said n-bit digital data and said m-bit digital data; and said reception unit further comprises: a demultiplexing means for demultiplexing a received digital data input signal into said n-bit digital data and said m-bit digital data.

Claim 5

The digital transmission system of claim 3, wherein said transmission unit further comprises; a first inverter for inverting said m-bit digital data and outputting said inverted m-bit digital data to said multiplexing means; and said reception unit further comprises: a second inverter for inverting said m-bit digital data which have been demultiplexed and outputting said inverted m-bit data to said digital/analogue conversion means; and a decision means for determining whether said demultiplexed n-bit digital data and said demultiplexed m-bit digital data have an identical fixed pattern.

Claim 6

The digital transmission system of claim 4, wherein said decision means comprises a means for determining the transmission abnormal if said demultiplexed n-bit digital data and said demultiplexed m-bit digital data have an identical fixed pattern.

Claim 7

The digital transmission system of claim 1, wherein each of said second, third and fourth low-pass filters band limits an audio signal into the same frequency band.

Claim 8

A digital transmission system for digitally transmitting an analogue base band audio signal, said digital transmission system comprising; a transmission unit having: a first low-pass filter for band limiting a first analogue audio signal into a second analogue audio signal with a predetermined frequency band; a second low-pass filter for band limiting said first analogue audio signal into a third analogue audio signal with a frequency band different from said second analogue audio signal; a first analogue/digital conversion means for converting said second analogue audio signal into n-bit digital data; a second analogue/digital conversion means for converting said third analogue audio signal into m-bit (m<n) digital data; a first inverter for inverting said m-bit digital data; and a multiplexing means for multiplexing said n-bit digital data and said m-bit digital data that has been inverted with said first inverter; and a reception unit having: a demultiplexing means for demultiplexing a received digital data input signal into said n-bit digital data and said m-bit digital data; a first digital/analogue conversion means for converting said demultiplexed n-bit digital data into a sixth analogue audio signal; a fourth low-pass filter for band limiting an analogue audio signal after passing through a fifth low-pass filter into said fifth analogue audio signal with a predetermined frequency band; a second inverter for inverting said demultiplexed m-bit digital data; a second digital/analogue conversion means for converting said digital data inverted with said second inverter into analogue data; a third low-pass filter for band limiting an output of said second digital/analogue conversion means into a fourth analogue audio signal with a predetermined frequency band; a first decision means for calculating a difference between an output level of said third low-pass filter and an output level said fourth low-pass filter and determining the transmission abnormal if the calculated difference is not less than a predetermined threshold value; and a second decision means for examining whether said n-bit digital data and m-bit digital data which have been demultiplexed with said demultiplexing means have an identical fixed pattern and determining the transmission abnormal if said n-bit digital data and said m-bit digital data have an identical fixed pattern.

Claim 9

A digital transmission system for digitally transmitting an analogue base band audio signal, said digital transmission system comprising; a transmission unit having: a first low-pass filter for band limiting a first analogue audio signal into a second analogue audio signal with a predetermined frequency band; a second low-pass filter for band limiting said first analogue audio signal into a third analogue audio signal with a frequency band different from said second analogue audio signal; a first analogue/digital conversion means for converting said second analogue audio signal into n-bit digital data; a second analogue/digital conversion means for converting said third analogue audio signal into m-bit (m<n) digital data; a first inverter for inverting said m-bit digital data; and a multiplexing means for multiplexing said n-bit digital data and said m-bit digital data that has been inverted with said first inverter; and a reception unit having: a demultiplexing means for demultiplexing a received digital data input signal into said n-bit digital data and said m-bit digital data; a first digital/analogue conversion means for converting said demultiplexed n-bit digital data into a sixth analogue audio signal; a fourth low-pass filter for band limiting an analogue audio signal after passing through a fifth low-pass filter into said fifth analogue audio signal with a predetermined frequency band; a second inverter for inverting said demultiplexed m-bit digital data; a second digital/analogue conversion means for converting said digital data inverted with said second inverter into analogue data; a third low-pass filter for band limiting an output of said second digital/analogue conversion means into a fourth analogue audio signal with a predetermined frequency band; a first decision means for calculating a difference between an output level of said third low-pass filter and an output level said fourth low-pass filter and determining the transmission abnormal if the calculated difference is not less than a predetermined threshold value; and a second decision means for examining whether said n-bit digital data and m-bit digital data which have been demultiplexed with said demultiplexing means have an identical fixed pattern and determining the transmission abnormal if said n-bit digital data and said m-bit digital data have an identical fixed pattern.

Claim 10

The digital transmission system of claim 7, wherein each of said third, fourth and fifth analogue audio signals has the same frequency band.

Claim 11

A supervisory method for monitoring transmission abnormalities in a digital transmission system for digitally transmitting an analogue base band audio signal, said supervisory method comprising: in a transmission side, a first and second band limiting step of band limiting a first analogue audio signal into predetermined frequency bands; a first and second conversion step of respectively converting the results of said first and second band limiting steps into n-bit digital data and m-bit digital data respectively, where m is less than n; a transmission step of transmitting said m-bit digital data together with said n-bit digital data that is a main signal; and in a reception side, a conversion step of converting said m-bit digital data into an analogue data signal; a third band limiting step of band limiting said analogue data signal into a predetermined frequency band; a fourth band limiting step of band limiting a second analogue audio signal obtained by analogue converting said n-bit digital data, resulting from said transmission step, into a predetermined frequency band; and a decision step of calculating a difference between an output level of a signal band limited in said third band limiting step and an output level of a signal band limited in said fourth band limiting step and determining the transmission abnormal if said calculated difference is not less than a predetermined threshold value.

Claim 12

A supervisory method for monitoring transmission abnormalities in a digital transmission system for digitally transmitting an analogue base band audio signal, said supervisory method comprising: in a transmission side, a first and second band limiting step of band limiting a first analogue audio signal into predetermined frequency bands; a first and second conversion step of respectively converting the results of said first and second band limiting steps into n-bit digital data and m-bit digital data respectively, where m is less than n; a transmission step of transmitting said m-bit digital data together with said n-bit digital data that is a main signal; and in a reception side, a conversion step of converting said m-bit digital data into an analogue data signal; a third band limiting step of band limiting said analogue data signal into a predetermined frequency band; a fourth band limiting step of band limiting a second analogue audio signal obtained by analogue converting said n-bit digital data, resulting from said transmission step, into a predetermined frequency band; and a decision step of calculating a difference between an output level of a signal band limited in said third band limiting step and an output level of a signal band limited in said fourth band limiting step and determining the transmission abnormal if said calculated difference is not less than a predetermined threshold value.

Claim 13

The supervisory method for monitoring transmission abnormality in a digital transmission system of claim 9, wherein each of said second third and fourth band limiting steps band limits an audio signal into the same frequency band.

Claim 14

The supervisory method for monitoring transmission abnormality in a digital transmission system of claim 9, wherein said transmission side further comprises: a multiplexing step of multiplexing said n-bit digital data and said m-bit digital data; and said reception side further comprises a second inverting step of inverting said m-bit digital data: and a demultiplexing step of demultiplexing received data into said n-bit digital data and said m-bit digital data.

Claim 15

The supervisory method for monitoring transmission abnormality in a digital transmission system of claim 11, wherein said transmission side further comprises a first inverting step of inverting said m-bit digital data and multiplexing said inverted m-bit digital data and said n-bit digital data; and said reception side further comprises a decision step of determining whether said demultiplexed n-bit digital data and said m-bit digital data have an identical fixed pattern.

Claim 16

The supervisory method for monitoring transmission abnormality in a digital transmission system of claim 12, wherein said decision step determines the transmission abnormal if said demultiplexed n-bit digital data and said m-bit digital data have an identical fixed pattern.