Note: Descriptions are shown in the official language in which they were submitted.
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Process for Transmitting a Time-variable Control Parameter
D E S C R I P T I O N
The invention relates to a process (method) according to
the preamble of patent claim 1. Such a process is known
from the "EBU Review-Technical", No. 218 (August 1986),
pages 2 through 12.
Radio broadcast audio signals are fed to the
transmitters with a dynamic (difference between the loudest
and quietest signals) which is adapted to the signal-to-
noise ratio of the subse~uent transmission path. However,
the dynamics resulting from this in many cases does not
correspond to the individual wishes of the radio listen~r~
Therefore, for example, when listening in a vehicle while it
is moving, the transmitted dynamic is m~ch too large owing
to ~he noise level in the vehicle, whereas, for example,
when listening via headphones, the transmitted dynamics,
normally lower then the original dynamics of the recorded
acoustic sîgnal, is too low.
In order to markedly improve the reproduction of the
audio signal, it is desirable to be able to adapt the
dynamics individually at the place of reproduction to the
wishes of the listener. For this, it is known ("EBU Review-
Technical", No. 218, August 1986) to derive a control
parameter (manipulated variable) from the program signal
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which then represents the restriction of the original
dynamics to a so-called ~target dynamic". ~Target dynamic"
is understood to be the restriction to a certain value, for
example, 30 dB, which is less than the transmitted dynamics.
This control signal is transmitted sychronized with the
associated program signal and evaluated in the receiver for
the variable dynamics selection. The free choice of dynamic
is rendered possible in that the "target dynamic" is
realized with the aid of the transmitted control parameter
or is further constricted (vehicle) or the original dynamics
is recreated through inverse utilization of the control
signal.
For transmitting the "variable dynamics" control signal
it is known (DE-PS 33 11 646 and DE-PS 33 11 647) to insert,
inaudibly, a fixed and a variable audio frequency with low
level at the lower frequency end of the S signal of an M/S-
coded stereophonic audio signal, whereby the frequency
separation of said frequencies represents the current
control parameter. However, the narrow-band filters
necessary for the demodulation of the frequency separation
do not allow rapid alterations to the control parameter;
further, the frequency range in the S signal provided for
the transmission of the control parameter is not
sufficiently interference-free in order to guarantee a
reliable transmission with the small signal levels used for
the audio frequencies. In particular, interference in the
frequency range concerned occurs through multipath reception
in the case of mobile reception.
Owing to these serious defects, a digital transmission
of the "variable dynamics" control signal is desirable in a
region of the transmission band of the broadcast signal
which is free from program signals. For the case of a
television sound signal, for e~ample, the blanking region of
the picture signal, already irl use for other digital
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auxiliary signals [videotext), could be considered as the
region free from program signals. An auxiliary carrier in
the multiplex channel offers itself ~or an FM signal;
howaver, there is the dif~iculty here that already the
identification signals for traffic program broadcasts as
well as the data stream for Radio Data System (RDS) are
transmitted at 57 kHz, and other auxiliary carriers are not
acceptable to the radio broadcast subscriber owing to the
expanditure relating to the decoder on the receiver side.
However, inserting the "variable dynamics" control signal
into the RDS data stream or the videotext data stream
respectively is is not possible because these data streams
are not broadcast sychroni~ed with the FM audio or
television sound signals respectively, something which runs
counter to the requirement for a synchronized transmission
of the "variable dynamicsl' control signal.
The object of the invention consists of creating a
process for transmitting the "variable dynamics" control
signal which, despite non-synchronized data stream
transmission, guarantees the necessary synchronization
between the control variabl~ and the program signal on the
receiver side.
This task is solved according to the invention by the
charactexizing features of patent claim 1.
Embodiments and further developments of the process
according to the invention ensue from the subclaims.
~ he process according to the invention is based on the
consideration that ~he ~variable dynamics~ control signal is
not isochronous with the program signal but, on the
contrary, leaves the broadcasting studio with a constant
advance of, for example, 1000 ms. This advance permits the
following method of functioning, explained by means of an
RDS data stream.
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The ~DS coder at the transmitter receives the control
signal and stores it. AS soon as the RDS coder has a free
group (sequence of data bits) available, the digitalized
control signal is transmitted as a data packet in this
group. The 37 net bits available in one group could be used
as follows:
32 bits ~or the transmission of the "variable dynamics~'
control parametex
5 bits for the identification of the time of
transmission.
The latter 5 bits specify by how many milliseconds the
transmission has been delayed in the ~DS coder or,
respectively, how much of the advance time has been
"consumed". This information allows the receiver to:
- temporally deaccentuate the data packet again and
convert it into individual discrete control signals with
constant temporal separation so that a constant control
data stream rasults at the end, and
- further delay ~hese data in a simple shift register
in such a way that the entire advance time is
compensated, and the constant control data stream is
again available, synchronized with the program signal.
The invention will be explained in more detail by means
of embodiment examples illustrated in the drawings. They
show in:
Fig. 1 a block circuit diagram of an installation
on the transmitter side for executing the
process according to the invention;
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Fig. 2 a block circuit diagram of an in~allation
on the receiver side for executing the process
according to th~ invention;
Fig. 3 a block circuit diagram of an installation,
modified compared to Fig~ 2, for executing a
variation of the process according to the
invention, and
igs. 4a through 4g diagrams for illustrating individual
steps of the process according to the invention.
The installation for executing the process according to
the invention on the transmitter side, illustrated
schematically by means of Fig. 1, shows a radio broadcast
studio 10 in which a radio broadcast program signal 11 and a
"Variable Dyna~ics" control signal 12 are generated. The
control signal 12 is here derived from the program signal,
as already explained above. The essential factor is that
at, or respectively, prior to the output from the studio 10,
a temporal delay of the program signal 11 with respect ~o
the control signal 12 is carried out, indicated in Fig. 1 by
a time function e]ement 13 with a constant delay time. This
delay leads to the con~rol signal 12 being in advance of the
associated program sec~ion of the program signal llo In
Fig. 4a, three program sections n, n+1 and n+2, each having
the same te~poral length, are plotted for an assumed time
sequence of a radio broadcast program signal. The ~Variable
Dynamics" contrcl signal is d~rived, for example, in the
form of discr~te scanning values, ~rom each program section
n or n+1 respectively. The scanning values for each program
signal segment are, as Fig. 4c shows/ combined in a digital
form into a data packet, whereby, at the time of the final
scanning value, the associated data packet begins in the
example presented.
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As also follows from Fig. 1, the program signal 11 and
the control signal 12 are transmitted to th~ transmitter
location 16 via separate lines 14 and 15 respectively. The
transmitter location 16 comprises, in the example presented,
an FM transmitter 17 as well as an RDS coder 18, whereby the
program signal 11 is sent to the transmitter 17 and the
advanced control signal 12 is sent to the RDS coder 18. The
RDS coder 18 inserts the data packets of the control signal
12, dela~ed by a variable time ~(deltaJ T, into its RDS data
stream, as is to be explained in more detail in the
following by means of Figs. 4d and 4e or 4f and 4g
respectively.
With the variation according to Fig. 4d, the data stream
stored in the ~DS coder 18 contains a cyclic sequence of
groups in which groups VD for inserting the "Variable
Dynamics~ control signal are already provided. The cycle
illustrated in Fig. 4d comprises the groups OA, VD, 2A, OA,
VD, 6A, OA, VD, 6~, 2A, OA, VD, 6A and 6A~ The insertion of
the data packets of the control signal allocated to the
program segments n, n+1 and n+2 is shown in Fig. 4e. In
this case some of the groups VD in the transmitted RDS data
stream reserved for the insertion of the control signal are
omitted if no data packets are present to be inserted for
these groups. This means, in the case o~ the example
according to Fig. 4d, that the groups VD with the current
group numbers 2 and 5 are not transmitted so that at the
time of the appearance of the data packet under
consideration for the current number n~ the data packets 1,
3, 4 and 6 have already been broadcast or, respectively,
(data packet No. 6) are just being broadcast. The next free
qroup VD is, therefore, group No. 8 so that the insertion of
data packet n must wait until group No. 7 has been broadcast
completely. This waiting time is designated ~tn in Fig. 4e.
The same considerations apply to the data packets with the
current numbers n~l and n~2, whereby in this case the
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waiting times ares designated ~tn+1 and ~tn+2 respectively.
As one can see by means of the waiting times plotted, the
waiting times are different owing to the structure of the
stored RDS data stream and can have, as a maxLmum, the
separation between two successive groups VD. As a result of
the respective waiting time ~t, the advance of the control
signal 12 is reduced, with respect to the associated program
signal segment, to the value ~ftau) -~t. As the program
signal and the control signal need to be synchronized in the
receiver, the waiting times ~t are recorded in the RDS coder
18 and transmitted in coded form in the data packet
concerned.
The transmitted RDS data s~ream is fed from the RDS
coder 18 to the transmitter 17 where it is transmitted on an
auxiliary carrier in the multiplex region of the program
signal according to the standard.
As an alternative to providing groups VD in the stored
sequence of RDS groups, it is also possible, according to
Fig. 4f, to do without such a provision, as is quire clear
from comparing Figs. 4d and 4f. One advantage of this is
that the sequence of groups (cycle) stored in the RDS coder
18 is considerably shorter than is the case in Fiq. 4d. If
a data packet is to be insert~d into the stored sequence of
RDS groups according ~o Fig. 4f, then this insertion is
performed at the end of the group just sent, whereby the
next group in the cycle is displaced by the duration of one
yroup. As Fig. 4g shows, the insertion of the data packet n
is carried out at the end of the group with the current
number 4 in the cycle 1, data packet n~l at the end of the
group with the current number 7 in the cycle 2 and data
packet n+2 at the end of the group with the current number 9
in the cycle 2. Likewise, from this there result waiting
times of ~tn, Atn+l and ~tn+2 respectively which, however,
are considerably shor~er when compared to the waiting times
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according to Fig. 4e. This represents another advantage of
the alternative according to Figs. 4f and 4g.
Using the installation on the receiver side illustrated
schematically by means of Fig. 2, the broadcast RDS data
stream is separated from the radio broadcast program signal
in the RDS-compatible receiver and fed to an RDS decoder 21
which demodulates and decodes the carried RDS data stream.
The decoded RDS data stream is passed on to the stage 22
(which may also form part of the decoder 21) where the
separation and evaluation of the ~Variable Dynamics" control
signal is carried out. When doing this, the information on
the waiting time ~t contained in each data packet is also
retrieved and this serves for controlling a subsequent
buffer memory 23 for the ~Variable Dynamics~ control signal.
The control signal appearing at the output of the buffer
memory 23 is once again synchronized with the associated
signal segment of the program signal which is fed from the
receiver 20 to a controlled amplifier 24. The control
signal occuring simultaneously at the control input of the
regulated amplifier 24 changes the amplification of the
program signal according to a manual input 25 for the
amplifier 24 so that the program signal reproduced via
loudspeaker 26 or non-illustrated headphones respectively
exhibits a dynamic corresponding to the individual wishes of
the listener or the manual specification at input 25
respectively. Hence, the execution of the procedure steps
according to Figs. 4a through 4g are carried out on the
receiver side in the reverse order to that of the
transmitter side.
A further embodiment example on the receiver side, based
on the idea that only a limited capacity is available in an
RDS transmission channel for transmitting the ~Variable
Dynamics" control signal, is illustrated in Fig. 3.
Nevertheless, in order to guarantee, in particular, a data-
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protected transmission in the RDS channel, typical control
signal progressions (forms) are permanently stored in a
memory 27 on the receiver side which is provided instead of
the buffer memory 23 according to Fig. 2. Merely the
addresses of the respective desired control signal
progressions are transmitted as the contents of the data
packets of the "Variable Dynamics" control signal, thereby
takiny up considerably less channel capacity than the
transmission of the control signal progressions as such. In
addition to the addresses of the permanently stored control
signal progressions, the control signal values actually
occuring on the boundaries of the program signal segments
and used in the memory 27 for the plausibility check and/or
correction and/or for initialization upon switching on the
device, changing program ox when the control signal is
unavailable can be transmitted. The saving in capacity
achieved with the help of this alternative technique is so
large that each data packet can be transmitted twice in the
RDS data stream, meaning a considerable increase in the
transmission relia~ility.
A table with examples of typical control signal
progressions is plotted ~elow the circuit block 27 in Fig.
3; the following can be seen:
a straight line with a gradient of 0 (constant dynamic~
a straight line with a positive gradient (climbing
dynamic)
a straight line with a negative gradient lfalling
dynamic)
signal leaps with various amplitudes, various directions
and occuring at various times (jump-type dynamic
alterations according to size, direction and time).
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