Note: Descriptions are shown in the official language in which they were submitted.
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PROGRAM OR METHOD AND DEVICE FOR DETECTING AN AUDIO
COMPONENT IN AMBIENT NOISE SAMPLES
BACKGROUND OF THE INVENTION
(0002) The present invention refers to a method for the compression of an
electric audio signal which is produced in the process of recording the
ambient noise
by means of an electroacoustic transducer, more particularly a microphone.
Furthermore, the invention also refers to a device for carrying out the
method.
(0003) In the field of audience research, which also comprises the acoustic
perception of other media such as e.g. television, recordings of the acoustic
environment of a panelist in a survey are used, i.e. the so-called hearing
samples.
The storage of these hearing samples on portable magnetic tape recorders is
disclosed in US 5,023,929. The inconvenience of this method is that the tape
recorder is relatively large although it is intended to be permanently carried
by the
participant.
(0004) Consequently, it would be preferable to integrate the hearing sample
recorder or monitor in an appliance which is normally worn or at least less
visible.
Such a possibility, namely the integration into a wristwatch, is mentioned in
EP-A-0
598 682 to the applicant.
(0005) However, the mentioned application does not indicate how the hearing
samples can be stored in the extremely narrow space and with the very limited
energy available in a wristwatch or a similarly inconspicuous appliance over a
considerable period of time such as at least a week. Although the
specification
mentions the need of compression procedures, known methods only are indicated.
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SUMMARY OF THE INVENTION
(0006) Some embodiments of the present invention provide a method for the
compression of hearing samples which in particular allows obtaining a high
compression with minimal efforts with the safe recognition of program elements
being
essentially conserved.
(0007) Some embodiments of the invention provide a method for the
compression of an electric audio signal which is produced in the process of
recording
the ambient noise by means of an electroacoustic transducer, more particularly
a
microphone, wherein
(0008) -the amplitude of said audio signal or of a derived digital or analog
signal is normalized to a first predetermined range D;
(0009) - said audio signal is mapped in the form of a non-linear mapping onto
a
second predetermined range of values W in order to obtain an emphasis of
sensitive
values; and
(0010) - the result is stored in an electronic memory in a digital form.
(0011) In the following, the same terminology as in EP-A-0 598 682 will be
used. A hearing sample is basically a recording of the ambient noise e.g. by
means
of a microphone. In order to simplify the storage as well as the transmission
to the
evaluating center, however, it is preferred to have a succession of short
recordings of
the ambient noise or hearing samples which are recorded at certain times.
Preferably, the recordings are effected at regular intervals of e.g. 1 minute,
and have
a constant duration of the order of, for example, 4 seconds, the information
of the
time of the recordings being stored together with the hearing sample.
(0012) According to some embodiments of the invention, the hearing samples
are finally stored in an electronic memory in a digitized form. According to
the
invention, in order to reduce the amount of data to be stored, a normalization
of the
hearing samples in their original form or in a derived form (filtered, limited
to selective
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frequency bands, digital or analog, etc.) to a predetermined range (of values
or
amplitudes) D and a subsequent nonlinear transformation on a second range W is
effected whose result, which is limited to the range W, is then stored in an
electronic
memory. The range W may be smaller or equal to D, but it is preferably
substantially
smaller.
(0013) Essentially, the non-linear transformation serves the purpose of
amplifying sensitive areas of range D in such a manner that the more
significant
information provided by a signal whose value is comprised in such a sub-range
of D
is emphasized in the result, i.e. its resolution is increased.
(0014) Preferred further developments of some embodiments of the invention
are as follows:
(0015) A: The nonlinear mapping is characterized by a decreasing slope
dW/dD for increasing values in D, e.g. similar to the logarithmic function.
Essentially,
the range of small values in D is thereby mapped onto a relatively larger
range in W
and thus emphasized, whereas relatively large values in D are mapped on a
relatively
small range in W only, i.e. their significance is attenuated.
(0016) B: The hearing samples are digitized immediately after recording (e.g.
by a microphone) and analog processing (amplification; coarse filtering in
preparation
of the analog-digital conversion, etc.), resulting in a succession of numeric
values.
Each numeric value represents e.g. the momentary loudness of the ambient noise
at
a determined time.
(0017) Further processing is effected digitally by digital circuits, program
controlled processors, or combinations thereof.
(0018) C: The amplitude or loudness values are transformed into energy
values e.g. by squaring. The energy values are submitted to a low pass
filtering and
subsequently differentiated, the differentiation preferably being simulated by
a
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difference calculus. The resulting energy variation values indicate the
variation of the
low-frequency proportion of the energy content in time.
(0019) D: The group of the energy variation values of a hearing sample, or
only a part thereof, is normalized with respect to the maximum value of the
values
within the (partial) group. For this purpose, the maximum value is determined
and all
values of the group are divided by this maximum value. Simultaneously, the
normalized values are mapped on a given range of numbers corresponding to the
range D, e.g. the numbers between -128 and +127, so that the following
arithmetic
operations involve only integers. The number of values in these numerical
ranges D
is therefore preferably equal to powers of 2 (in the example: 256 = 28 values)
which
are particularly advantageous in the case of binary digital processing. In
order to
perform this combination of normalizing and of
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imaging, the values of a group are multiplied by a factor which results from
the division of
the limit of the numeric range (i.e. 128 in the example) by the maximum value
within the
group.
(0020) E: The results of this step are again mapped on a further, smaller
range of
values W, e.g. the numerical range from 0 to 15 comprising 24 = 16 numbers. On
account
of the fixed and relatively small number of values of the input data of this
step, a so-called
look-up table may be used for this second mapping.
(0021) Overall, it follows from the preceding that each numerical value of the
hearing samples is reduced to a relatively short binary number (of 4 bits in
the example).
(0022) F: Further optimizations are applied, such as e.g. taking the mean
value of a
plurality of values, only the mean value being further used. This also results
in an
important reduction of the number of values to be processed. On the digital
level, such a
filtering is simulated by a convolution.
(0023) G: Before or after being digitized at the input, the hearing sample is
split into
frequency bands or band signals. In a known manner, digital filterings may be
effected by
convolutions, and since the preferred convolutions represent low pass
filterings, it is
preferable to transmit less values to the following processing stages than are
used for the
convolution, preferably only one respective value.
According to an aspect of the invention, there is provided method for
evaluating recorded hearing samples recorded by at least one first device, the
method
comprising recording, by a second device, a plurality of samples of programs
to be
monitored wherein each of the samples of programs to be monitored has a
greater duration
than a corresponding one of the recorded hearing samples, and calculating a
first
correlation for comparing the hearing samples with the program samples in
order to find a
match.
According to another aspect of the invention, there is provided a computer
program which when run on a computer executes the method of evaluating
recorded
hearing samples recorded by at least one first device, the method comprising
recording, by
a second device, a plurality of samples of programs to be monitored wherein
each of the
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samples of programs to be monitored has a greater duration than a
corresponding
one of the recorded hearing samples, and calculating a first correlation for
comparing
the hearing samples with the program samples in order to find a match.
According to one aspect of the present invention, there is provided a
method for evaluating hearing samples of ambient noise recorded by at least
one first
device in at least one first location where programs to be monitored are
received, the
hearing samples being obtained by a method comprising recording samples of an
ambient noise using a sound transducer, the sample duration being shorter than
the
sampling cycle, the method for evaluating hearing samples comprising
recording, by
at least one second device in at least one second location where the programs
to be
monitored are broadcast, a plurality of samples of the programs to be
monitored
wherein each of the samples of programs to be monitored has a greater duration
than
a corresponding one of the recorded hearing samples, and calculating a first
correlation for comparing the hearing samples with the program samples in
order to
find a match, a match occurring if a program sample is considered to be
contained in
a hearing sample, each of the hearing samples being taken during a respective
first
period of time completely included in a respective second period of time
during which
a corresponding one of the program samples is taken.
According to another aspect of the present invention, there is provided
a computer-readable storage medium having computer-executable instructions
stored thereon that, when executed by a computer, causes a processor of the
computer to perform a method of evaluating recorded hearing samples of ambient
noise recorded by at least one first device in at least one first location
where
programs to be monitored are received, the hearing samples being obtained by a
method comprising recording samples of an ambient noise using a sound
transducer,
the method of evaluating the recorded hearing samples comprising recording, by
at
least one second device in at least one second location where the programs to
be
monitored are broadcast, a plurality of samples of the programs to be
monitored
wherein each of the samples of programs to be monitored has a greater duration
than
a corresponding one of the recorded hearing samples, and calculating a first
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correlation for comparing the hearing samples with the program samples in
order to
find a match, a match occurring if a program sample is considered to be
contained in
a hearing sample, each of the hearing samples being taken during a respective
first
period of time completely included in a respective second period of time
during which
a corresponding one of the program samples is taken.
According to still another aspect of the present invention, there is
provided a method for evaluating hearing samples recorded by at least one
first
device in at least one first location where programs to be monitored are
received, the
hearing samples being obtained by a method comprising recording samples of an
ambient noise using a sound transducer, the method for evaluating hearing
samples
comprising recording, by at least one second device in at least one second
location
where broadcast signals of the programs to be monitored can be recorded, a
plurality
of samples of the broadcast signals of the programs to be monitored wherein
each of
the samples of programs to be monitored has a greater duration than a
corresponding one of the recorded hearing samples, and calculating a first
correlation
for comparing the hearing samples with the program samples in order to find a
match, a match occurring if a program sample is considered to be contained in
a
hearing sample, each of the hearing samples being taken during a respective
first
period of time completely included in a respective second period of time
during which
a corresponding one of the program samples is taken.
According to yet another aspect of the present invention, there is
provided a computer-readable storage medium having computer-executable
instructions stored thereon that, when executed by a computer, causes a
processor
of the computer to perform a method of evaluating recorded hearing samples of
ambient noise recorded by at least one first device in at least one first
location where
programs to be monitored are received, the hearing samples being obtained by a
method comprising recording samples of an ambient noise using a sound
transducer,
the method of evaluating the recorded hearing samples comprising recording, by
at
least one second device in at least one second location where broadcast
signals of
the programs to be monitored can be recorded, a plurality of samples of the
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broadcast signals of the programs to be monitored wherein each of the samples
of
programs to be monitored has a greater duration than a corresponding one of
the
recorded hearing samples, and calculating a first correlation for comparing
the
hearing samples with the program samples in order to find a match, a match
occurring if a program sample is considered to be contained in a hearing
sample,
each of the hearing samples being taken during a respective first period of
time
completely included in a respective second period of time during which a
corresponding one of the program samples is taken.
According to a further aspect of the present invention, there is provided
a method for evaluating hearing samples of ambient noise recorded by at least
one
first device in at least one first location where programs to be monitored are
received,
the hearing samples being obtained by a method comprising recording samples of
an
ambient noise using a sound transducer, the method for evaluating hearing
samples
comprising recording, by at least one second device in at least one second
location
where the programs to be monitored are broadcast, a plurality of samples of
the
programs to be monitored wherein each of the samples of programs to be
monitored
has a greater duration than a corresponding one of the recorded hearing
samples,
and calculating a first correlation for comparing the hearing samples with the
program
samples in order to find a match, a match occurring if a program sample is
considered to be contained in a hearing sample, each of the hearing samples
being
taken during a respective first period of time completely included in a
respective
second period of time during which a corresponding one of the program samples
is
taken.
BRIEF DESCRIPTION OF THE DRAWINGS
(0024) The invention will be explained in more detail hereinafter by means of
an exemplary embodiment and with reference to figures.
(0025) Fig. 1 shows a block diagram of a monitor according to the invention;
(0026) Fig. 2 shows the division into frequency bands;
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(0027) Fig. 3 shows the conversion into energy values and the differentiation;
(0028) Fig. 4 shows the "normalizing quantization".
DETAILED DESCRIPTION OF THE INVENTION
(0029) Fig. 1 shows a block diagram of a monitor 1. It may e.g. be intended to
be integrated in a wristwatch, which is why monitor 1 comprises a clock
circuit 2
which also serves as a time base for the signal processing, as well as a
(liquid
crystal) display 3. Commercially available components may be used for circuit
2 and
display 3. A precise clock signal is generated by a quartz 4 in conjunction
with an
oscillator circuit which is integrated in clock circuit 2. Since a highly
precise timing is
required for the synchronization of the hearing samples to the comparative
samples,
a temperature compensation is provided in addition. The latter comprises a
temperature sensor 5 which is connected to the clock circuit by means of an
interface
circuit 6. Interface circuit 6 essentially comprises an A/D converter.
(0030) Another important element for the monitor function is wearing
detector 7. It may essentially consist of a sensor area on the wristwatch
which
detects the contact with the skin of the wearer. In the example, wearing
sensor 7 is
connected to clock circuit 2 by means of an interface circuit 8, which implies
that the
clock circuit is capable of providing the time indications with an additional
mark from
the wearing sensor. It is also conceivable to directly connect the wearing
sensor to
the proper monitor circuit, e.g. to digital signal processor 9.
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(0031) The clock signals which are required for the signal processing, in
particular
for signal processor 9, are derived from the time base clock, which is taken
from a
connection 10 of quartz 4, by a PLL (phase locked loop) circuit 11. The time
and the date
as well as the mark from the wearing sensor, as the case may be, are
transmitted from
clock circuit 2 to digital signal processor 9 by a serial data connection 12.
(0032) The hearing samples are stored in a flash memory 13. It is an important
advantage with respect to the present application that flash memories are
capable of
storing data in a non-volatile manner and of deleting them again without the
need of
particular measures. A bus 14 allowing to transmit both data and addresses
serves to
connect flash memory 13 and signal processor 9.
(0033) A multiplexer 16 is connected by a second serial connection. Depending
on
the operational condition, the multiplexer connects signal processor 9 to the
recording unit
of the hearing samples or to interface circuit 17 by means of which the data
exchange with
the evaluating center is effected.
(0034) The recording unit consists of a microphone 18 and a following A/D
converter unit 19 which in addition to the proper A/D converter may comprise
amplifiers,
filters (anti-aliasing filters) and other usual measures in order to ensure a
digital signal
which represents the recording by the microphone as correctly as possible.
(0035) Power supply 20 may be a battery (lithium cell) or the like. An
accumulator
in conjunction with a contactless charging system by means of electromagnetic
induction
or a photo cell is also conceivable.
(0036) To ensure the connection to the exterior, more particularly for the
transmission of data to the evaluating center, monitor 1 is provided with a
bidirectional
data connection 21, a reset input 22, a synchronization input 23, and a power
supply
terminal 24. The presence of a power supply at terminal 24 is also used to
make the
monitor change to the data transmission mode. For example, the monitor may be
connected to a base station which establishes a connection to an evaluating
center e.g. by
telephone. Another possibility consists in mailing the monitor to the center
where it is
connected to a reading station. On this occasion, besides the data
transmission, a
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synchronization of clock circuit 2 to the clock of the center may be effected,
as previously
described in EP-A-0 598 682.
(0037) As shown in the illustration, the hearing sample processing unit
including
signal processor 9 and the necessary accessory components (multiplexer 16,
memory 13,
clock generator consisting of PLL circuit 11 and quartz 10, etc.) may be
composed of
discrete components. In order to be incorporated in a wristwatch, however, the
functions
must be integrated in as few components as possible, which may result in a
single
application specific circuit 30 in the extreme case. For example, signal
processors of the
TMS 320C5x series (manufacturer: Texas Instruments) may be used, in which
multiplexer
16 is already contained, inter alia, and Flash RAMs of the type AM29LV800
(manufacturer: Amdahl) having a capacity of 8 MBit. Such a memory capacity and
the
application of the compression method for hearing sample data according to the
invention
as described hereinafter allow to attain an uninterrupted operation of the
monitor for
approx. 7 days.
(0038) In view of energy consumption, it is advantageous if the hearing sample
processing unit, more particularly signal processor 9, is only periodically
switched on. If
e.g. one hearing sample per minute is taken, it is sufficient according to the
processing
method of the present invention to switch on the power supply of the signal
processor for
some seconds (less than 5, e.g. 4 seconds) only. For this purpose, the power
supply
receives an on-signal 25 from clock circuit 2 during whose presence the
hearing sample
processing unit is supplied with current. A further reduction of the energy
consumption is
obtained by the fact that flash memory 13 is only supplied with the current
required for the
storing process for a short time, 3 milliseconds at the end of each processed
hearing
sample recording being sufficient in the case of the above-suggested type. The
signal
required therefor is generated by signal processor 9 and transmitted along bus
14. The
program controlling the signal processor is contained in a separate program
memory which
may be integrated in the signal processor itself, so that the hearing sample
processing
operation can also be performed while flash memory 13 is off.
(0039) Hereinafter, the method for the processing of the hearing samples is
described. After the recording of the ambient noise (microphone 18) and its
analog-digital
conversion according to known principles (A/D converter unit 19), a splitting
into e.g. six
frequency bands is performed (Fig. 2) which is effected by a hierarchical
arrangement of
*Trade-mark
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low passes 30 - 35. The required high pass associated to each low pass is
realized by a
subtraction 36 - 41 of the output signals 42 - 47 from the respective input
signals 48 - 53 of
the low passes, the subtraction being effected by an addition of the inverted
output signals
42 - 47 of low passes 30 - 35.
(0040) Low pass filters 30 to 35 are realized by a 19-digit convolution:
18
yj = I ai xj-i (~1
i=0
where
(0041) j : time index
(0042) y: output value of the low pass filtering at the time j;
(0043) x: input value for low pass filtering at the time j;
(0044) a: coefficient of the convolution sequence;
(0045) ao...a18:[0.03, 0.0, -0.05, 0.0, 0.06, 0.0, -0.11, 0.0, 0.32, 0.50,
0.32, 0.0, -0.11,
0.0, 0.06, 0.0, -0.05, 0.0, 0.03]
(0046) In the course of the splitting into the frequency bands or band signals
(54), a
first data reduction is already effected in that only every second value out
of each sequence
of output values of the high and low pass filterings is transmitted to the
following low
resp. high pass stage or to outputs 54 by the switches 55. Overall, this
already allows to
obtain a reduction of the data volume to 1/8. With the division into six bands
used in the
example, this results in a slight overcompensation of the accompanying
increase of the
data volume by a factor six.
(0047) A criterion for the design of the filters is that one band may contain
the
contents of every other band in a clearly attenuated form at the most. A
reduction to the
half at least may be considered as clearly attenuated. Ideally, the bands only
contain
residual portions of directly adjacent bands, portions which are near or below
the
resolution of the digital numerical representation even. In the preferred
digital realization,
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this aim is attained by low pass filtering (convolution) and subsequent
subtraction of the
filtered proportion from the input signal of the low pass filter.
(0048) The treatment of the band signals 54 resulting from the division into
bands is
identical in each band, Figs. 3 and 4 showing the processing of only one band
56 in a
representative manner.
(0049) Input signal 56, which is identical to output signal 54, is first
squared in that
it is supplied to the two inputs of a multiplier 57 in parallel. Except a
proportionality
factor, this squaring corresponds to a calculation of the energy content of
the proportion of
the ambient noise which is represented by signal 56. Energy values 58 are
subjected to a
low pass filtering. This filtering is realized by means of a convolution over
48 values:
47
Yj bi xj-i (2)
i=0
where
(0050) j: time index of the ye and xe values;
(0051) x~ : energy value 58 at the time j;
(0052) y,~: output signal of the low pass filter 59 at the time j;
(0053) b;: the coefficients of the convolution sequence, wherein
bo=b1=...=b47=1.00.
(0054) Of the output values of low pass filter 59, only every 48th value is
forwarded
to the following differentiation 61 by switch 60. Overall, here, a data
reduction to 1/48 of
the input data volume is obtained by the formation of a mean value.
(0055) In differentiator 61, each incoming value is delayed by a time unit in
delay
unit 62. Delay unit 62 may e.g. be a FIFO waiting queue having a length of 1.
(0056) In adder 63, the undelayed values are added to the inverted, delayed
values,
so that the values of the differences between two successive input values of
the
differentiator 61 are available at the output 64. The differences refer to a
determined,
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constant and known time shift which is given by the time units, and
consequently represent
an approximation of the derivative with respect to time.
(0057) The energy difference values 64 are subjected to the normalized
quantization.
On one hand, according to Fig. 4, the absolute value of the energy difference
values is
formed in absolute value unit 65. These absolute values are supplied to a
maximum value
detector 66 at the output 67 of which the greater one of the values supplied
to its inputs 68
appears. Since the output signal from output 67 is fed back to one of the two
inputs 68 by
a single-stage delay circuit 69, the maximum value of all values received by
absolute value
unit 65 is formed at output 67. The maximum values pass through another switch
70
which only transmits every 32nd value, i.e. a value which is the greatest
within a hearing
sample (the hearing sample duration used in this embodiment results in 32
energy
difference values 64 per hearing sample in each frequency band).
(0058) In a reciprocal-computing and multiplication unit 71, the number 128 (=
27)
is divided by the maximum value of the hearing sample and the result is
supplied to an
input 72 of a multiplicator 73. The other input of multiplicator 73 is then
successively
supplied with the energy difference values 64 among which the maximum value
has been
determined. For this purpose, the difference values 64 are temporarily stored
in a FIFO
buffer 75. The result of the multiplication in multiplicator 73, whose values
are comprised
between -128 and +127, is converted by converter 76 into integers in the range
D from 0
to 255, corresponding to a byte having 8 bits. These numbers are used as
addresses in a
look-up table (LUT) 77 where a number in the range W = 0 to 15, i.e. a four-
digit binary
number, is associated to each input value. The discrete mapping of 8-bit
numbers onto
4-bit numbers performed in LUT 77 is nonlinear and so designed that the
resolution of
small input numbers is finer than that of greater input values, i.e. that
small input values
are more emphasized. This may be referred to as a non-equidistant
quantization.
(0059) The 4-bit values from output 78 are stored in flash memory 13 (Fig. 1).
(0060) The described normalized, non-equidistant quantization and compression
unit
is provided for each band according to the illustration of Fig. 3, resulting
in 4-bit values
for a total of 32 x 48 x 8 =12,288 values per processing cycle which are
recorded by the
A/D converter at input 48 (Fig. 2). With an A/D conversion rate of 3,000 to
5,000
conversions per second, as provided by the currently available A/D converters
of the
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lowest power consumption, this results in a hearing sample duration of approx.
2.5 to 4 s.
With a supposed rate of one hearing sample per minute, the necessary memory
capacity
for the data amounts to 32 x 6 x 4 = 768 bit/min or 1'105'920 bit/d. The
indicated 8 Mbit
memory thus allows to record approx. 7 days of uninterrupted operation of the
monitor.
(0061) In view of a reduction of the required computing, all cited
calculations are
effected by integer or fixed point arithmetic unless especially indicated, in
particular an
exponential representation of floating point numbers is avoided. The number of
bits used
for the representation of a number essentially depends on the used processor
and on the
data length provided by the latter. The above-mentioned processor family
TMS320C5x
uses 16-bit arithmetic. The binary point for fixed point arithmetic is set in
such a manner
that the limited computing accuracy is optimally utilized in each processing
step although
the probability of a data overflow is extremely low. Therefore, the binary
point is set
differently in the different processing steps. In the preferred embodiment of
the band
division, the least significant bit represents the value 2-16 for the filter
coefficients and the
value 2 for the data values. Energy conversion and energy filtering are
calculated by
32-bit integer arithmetic which is implemented as standard library function
calls.
(0062) Prior to the storage in the flash memory or alternatively in the
evaluating
center, usual compression methods may be additionally applied which allow
restoration of
the original data in an identical form when decompressed.
(0063) In preparation of the recognition of the program elements which are
possibly
contained in the hearing samples, program samples are as exactly
simultaneously as
possible taken, e.g. directly at the broadcasting station, and stored. Prior
to their
comparison, the program samples are preferably subjected to the same
processing and
compression process as the hearing samples. This may be the case before the
storage or
only at the time of reading resp. playback of the stored program samples.
(0064) For the recognition, one of the usual correlation methods may be used.
It is
also possible to apply a coarse correlation using a fast computing procedure
first and to
perform a more precise and complicated correlation only if a sufficient
probability of the
presence of a given hearing sample has been found. In particular, such a
preceding coarse
correlation also provides a first coarse estimate of a subsisting minimal time
shift between
the hearing sample and the reference samples recorded at the station. In the
more complex
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procedure, finer time shifts are analyzed and a more rugged comparison method
is applied
which takes account of the statistical distribution of the program signal and
of interference
signals.
(0065) Essentially, in the course of the evaluation, the simultaneous captured
samples of each program as recorded each by a stationary unit are compared to
the hearing
samples of each monitor. An exemplary comparison method is illustrated in the
following
pseudocode which describes the correlation of a hearing sample of a monitor:
Decompress data of the monitor
OptimumMatch := -1
FOR StationaryUnit := 1 TO NumberOfStationaryUnits DO
Load digitized program samples which have been recorded at the same time
as the hearing samples of the monitor;
Apply same preliminary processing as to hearing samples;
FOR TimeShift := 1 TO MaxTimeShift STEP Timestep DO
{Takes account of running inaccuracies of the timers by a step size of
Timestep}
Calculate matching coefficient ct with standard correlation for the
actual time shift and assign result to the variable ActualMatch;
IF (ActualMatch > OptimumMatch) DO
OptimumMatch := ActualMatch;
OptimumTimeShift := TimeShift;
OptimumStationaryUnit := Stationary Unit;
ENDIF
ENDFOR
ENDFOR
IF(OptimumMatch > Threshold) DO
RadioStation is recognized;
The correct station is stored in the memory
OptimumStationaryUnit
ELSE
None of the surveyed reference programs was heard at this time
ENDIF
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(0066) In this procedure, only one of the radio programs registered in
'NumberOfStationaryUnits' is determined in the hearing sample of a monitor,
namely the
one which yields the highest probability (value of the variable
'OptimumMatch').
(0067) In particular, the optional, univocally reversible compression of the
hearing
samples processed according to the invention is reversed. This is followed by
the
initialization of 'OptimumMatch'to the lowest value which also indicates "no
match", i.e.
the wearer of the monitor has listened to none of the monitored programs.
(0068) The program samples of each stationary unit simultaneously recorded
with
the current hearing sample (loop "For StationaryUnit:= 1 to
NumberOfStationaryUnits ...
EndDo" are loaded and processed in the same manner as the hearing sample. Due
to
subsisting small time shifts between the hearing samples and the program
samples, the
following comparison is performed for a certain number 'MaxTime Shift' of
assumed time
shifts (loop "For TimeShift := I to MaxTimeShift ... Endfor"). The comparison
is effected
by a standard correlation of program and hearing sample data which are shifted
forwards
or backwards with respect to each other according to the 'TimeShift' variable.
In order to
always allow a full correlation over all values of the hearing sample, the
program samples
are therefore recorded over a longer period per sample, the beginning being
additionally
set earlier in time by the corresponding maximum time shift. Correspondingly,
the length
of the program sample is chosen in such a manner that the hearing sample is
still
completely contained in the program sample time even if the beginnings of the
program
sample and of the hearing sample are maximally displaced.
(0069) The normalized correlation is performed according to the following
formula:
N
(Si mi-t)
C i=1
t N N (3)
(Si)2 (mi-t)2
i=1 i=1
where
(0070) t: time shift index (='TimeShift' in pseudocode);
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(0071) N: number of correlated values, generally equal to the number of values
in a
hearing sample;
(0072) is time index;
(0073) si: hearing sample value at the time i;
(0074) m;-t: program sample value at the time i, displaced by t time steps;
(0075) ct: correlation value for the time shift t: -1 <_ ct <_ 1.
(0076) The ct values for different t values and program samples are compared,
and
the greatest ct value overall is stored along with the indications of the
conditions in which
it has been recorded. These indications consist of the time shift, the
stationary unit, i.e. the
program, and of the correlation value ct itself.
(0077) If the so determined greatest ct value is superior to a predetermined
threshold
value, the corresponding program is considered to be contained in the hearing
sample. If
the threshold value is not attained, it is assumed that no one of the programs
was heard.
(0078) Since the correlation must be performed correspondingly often due to
the
considerable scope of time shifts (t resp. TimeShift), a simplified
alternative is conceivable
where the time intervals are treated with a coarser graduation. For those ct
values which
exceed a predetermined threshold, the correlation is repeated with a more
rugged method
while taking account of all detected time shifts.
(0079) A suitable rugged correlation is
N
Isi - a*mi-t
rt = i-1 N (4)
Si
i=1
where
(0080) rt: "rugged" correlation value;
(0081) a: scaling factor which takes account of the attenuation of the program
signal
with respect to the hearing sample;
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the remaining symbols corresponding to formula (3).
(0082) The procedure thus essentially uses absolute values both of the
deviation
between the hearing sample and the scaled program signal and of the hearing
sample
signal. The scaling factor a is iteratively determined in such a manner that
the rugged
correlation value rt becomes minimal. Compared to the normal correlation,
large
deviations are less weighted in the rugged correlation, thus taking account of
statistical
distributions of hearing sample values and of program signal values and
therefore resulting
in better recognition rates for real signals than the normal correlation value
ct. In
particular, individual hearing samples with large deviations are less
weighted.
(0083) Tests show that the described method not only eliminates or at least
strongly
reduces known interference effects such as secondary noise and time shifts but
that
damping (speakers, transmission lines, general acoustic conditions) and echo
as well have
only little influence on the recognition of a program. It has been
particularly surprising to
find that the program could often be detected in the hearing samples even when
the
program element was inaudible. The suppression of echo effects is attributed
to the
formation of a temporal mean (filter 59), in particular, especially if its
time constant is
chosen in such a manner as to be greater than the echo times usually found in
a normal
environment. A typically frequency-dependent (acoustic) damping is compensated
by the
described suitable combination of a division into frequency bands, a
normalization to the
maximum value, and in taking into account of the damping by means of the
scaling factor
a in the calculation of rt or by the calculation mode of ct.
(0084) Modifications of the exemplary embodiment within the scope of the
invention are apparent to those skilled in the art.
(0085) According to the technological development, different components
(signal
processors, memories, etc.) may be used. Alternatives are conceivable in
particular for the
flash memory, e.g. battery-backed up CMOS memories. The criteria, especially
for
portable monitors such as wristwatches, are an extended uninterrupted
monitoring period
and a minimal energy consumption. In certain circumstances it may be better to
use a fast
processing unit having a higher power dissipation if the higher energy
consumption with
respect to a slower unit is more than compensated by only temporary operation
with
intermediate inactive pauses. Besides the complete shut-off, many components
such as
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e.g. the TMS320C5xx also offer special power saving modes. Also, the reduction
of the
clock rate of a fast unit often allows an important reduction of the energy
consumption.
(0086) Depending on the used technology, different degrees of accuracy or
numbers
of digits of the binary numbers may be used. In tests, a sufficiently safe
program
recognition has been obtained with 4-bit end results. It is also conceivable,
however, to
effect a reduction to 3 bits, or to provide a greater number, e.g. 6 bits, 7
bits, or 8 bits.
Greater numbers of binary digits are possible in particular if shorter wearing
times are
allowed or if memories of greater capacity become available.
(0087) In the case of higher numbers of digits of the end result, it may also
be
necessary to increase the number of digits in the preceding steps to the
number of digits of
the end result at least.
(0088) Mostly, the exact values for the nonlinear mapping by table 77 as well
as the
threshold values for the weighting of the correlation values can only be
determined
empirically. Although a function similar to a logarithmization is preferred,
other functions
are possible. It is also conversely conceivable to emphasize the greater
values in D and to
suppress the small values of the energy differences.
(0089) The factors and the number of digits of the convolutions may as well be
chosen differently, and a different number of frequency bands into which the
hearing
samples are split is possible. In particular, it is conceivable in the case of
modified A/D
conversion speeds, different settings with respect to echo and/or damping
compensation,
or modified hearing sample durations, to adapt low pass 59, e.g. by changing
the number
of tabs of the convolution.
(0090) It is also conceivable to perform the analog-digital conversion at a
later stage
of the compression, particularly if the corresponding analog circuits offer
advantages with
respect to the processing speed or the space consumption in the monitor. In
the extreme
case, the digitization might be effected only immediately prior to the storage
in the
memory. If an analog signal is concerned, the term "digital value" in the
description shall
be replaced with e.g. the size or the amplitude of the signal.
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(0091) With respect to the correlation, it is also possible to use only the
part of the
hearing samples which still lies within the corresponding program sample with
the actual
time shift t, e.g. if program and hearing samples of the same length are
recorded.
(0092) An alternative of the wearing sensor consists of using currently
available
motion sensors. A known embodiment contains a contact which switches between
the
open and the closed state on motion but remains in one of the two states in
the absence of
motion.
GLOSSARY
(0093) Flash RAM RAM (see there) which also conserves data in case of power
failure but allows faster storage and easier erasure than classic non-volatile
memories
(PROM/EPROM).
(0094) RAM read/write memory
(0095) time index number of a digital value in the succession of values
leaving
the digitizer (A/D converter), mostly in relation to the beginning of a
hearing sample,
whose associated value has the time index 0.
