NL2007413C2 - Digital signal processing method for processing a composite myoelectric signal. - Google Patents

Digital signal processing method for processing a composite myoelectric signal. Download PDF

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NL2007413C2
NL2007413C2 NL2007413A NL2007413A NL2007413C2 NL 2007413 C2 NL2007413 C2 NL 2007413C2 NL 2007413 A NL2007413 A NL 2007413A NL 2007413 A NL2007413 A NL 2007413A NL 2007413 C2 NL2007413 C2 NL 2007413C2
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signal
filtering
intermediate signal
moving
seconds
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NL2007413A
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Leo Eijkern
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Inbiolab B V
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Priority to PCT/NL2012/050639 priority patent/WO2013039391A1/en
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
    • A61B5/316—Modalities, i.e. specific diagnostic methods
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
    • A61B5/316—Modalities, i.e. specific diagnostic methods
    • A61B5/389—Electromyography [EMG]

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Description

DIGITAL SIGNAL PROCESSING METHOD FOR PROCESSING A COMPOSITE MYOELECTRIC SIGNAL
5 The invention relates to a digital signal processing method for processing a composite myoelectric signal Scm, which composite myoelectric signal Scm is measured using passive measuring electrodes applied over the muscle to be measured of a living being, for quantifying changes in amplitude of the composite myoelectric signal Scm which resembles a quasi noise source NSQ, which quasi noise source NSQ represents the firing of motor units of 10 a muscle during muscle contractions and which quasi noise source NSQ has variable amplitude properties, representing variations in muscle force.
A digital signal processing method according to the preamble is known in the art and is used in for example to measure muscle fatigue in muscles of the living being. The method is for example used in sports, physiotherapy, medical treatment, etc. Motor units fire 15 randomly at different frequencies and amplitudes resulting in a quasi noise component in the myoelectric signal Scm- It is found that the amplitude properties of the quasi noise component resembles filtered white noise within a given bandwidth. It is also found that during fatigue of the muscle the firing characteristics of the motor units of a muscle change from mainly random towards mainly synchronized. This phenomenon is thus an indicator for muscle 20 fatigue. The more fatigue a muscle gets, the higher the level of synchronization in motor units firing. The myoelectric signal therefore is losing the more or less smooth amplitude shape towards a more erratic looking shape.
To quantify the change in amplitude of the composite myoelectric signal Scm the ratio of the root mean square (RMS) and the absolute mean of the myoelectric signal, the so called 25 Waveform Factor (WFF) is used: WFF= x™s | X | mean
The more erratic the myoelectric signal, the higher the WFF. For example, a sine wave has a WFF of 1.11, whereas the WFF of random noise is 1.24.
30 A drawback of the known method is that the method is only valid for a myoelectric signal, which only contains the above mentioned quasi noise component. For example, in isometric muscle contractions, where there is no change in length of the muscle, no change on load on the muscle and no movements at the joints that can cause such a signal.
However, when the myoelectric signal contain one or more signal components from 35 other sources, like for example in non-isometric muscle contractions, the abovementioned method is not suitable and leads to incorrect results.
In non-isometric muscle contractions, the calculation of the WFF of a moving muscle 2 is highly dominated by the shape of the modulation of the neural drive generating the movement. This results in a variable muscle tone expressed as a variable amplitude, which has a modulation effect on the WFF.
Given the unknown summation of the firing properties of a fatigue muscle and shape 5 and size of the movements it is not possible with the known method to measure the state of fatigue during motion.
It is an object of the invention to provide a digital signal processing method according to the preamble which can reliable detect firing properties of the muscle during motion.
The invention therefore provides a digital signal processing method according to the 10 preamble, characterized in that the method comprises the following steps: a) generating a noise signal NS from an external noise source, which has invariant amplitude properties; b) filtering the myoelectric signal Scm! which is performed by a noise filter for filtering the quasi noise source NSQ with a time window of Tf1 seconds and which filter means generates 15 a first intermediate signal Sn.
c) mixing the first intermediate signal Sn with the noise signal NS, which mixing generate a reference signal Sref.
d) quantifies the changes in the statistical properties of the quasi noise source NSq by comparing signal SrefWith signal Scm- 20 Most preferably, the external noise source is implemented in software.
To separate the movement modulations which are present on the neural drive of muscles (EMG) from underlying motor units, a model of the EMG signal is used that is based on a noise source modulated by the envelope of the neural drive of a moving muscle. Therefore the reference signal Sref contains only noise from the external noise source with 25 invariant amplitude and frequency and quasi firing properties with the same amplitude envelope as the quasi noise source. By comparing the statistical properties of this signal with the statistical properties of the myoelectric signal Scm, which contains noise from the quasi noise source but with variant amplitude properties, a quantification can be made of the changes in firing properties of the quasi noise source NSQ.
30 In a first preferred embodiment of the digital signal processing method according to the invention the following steps are further taken: in step b) the filtering is performed by either moving absolute mean filter means or root mean square (RMS) filter means.
in step c) the first intermediate signal Sn is multiplied by the noise signal NS, which 35 multiplication generate a reference signal Sref- in step d) a ratio or a derivate thereof is calculated between the RMS of the myoelectric signal Scm and the RMS of the reference signal Sref or between the moving absolute mean of 3 the myoelectric signal Scm and the moving absolute mean of the reference signal Sref, whereby the ratio quantifies the changes in statistical properties of the quasi noise source NSq.
The moving absolute mean filter means and root mean square (RMS) filter are both 5 common noise filtering techniques and allow for substantially removal of the noise coming from noise source NSq. By multiplying this signal with the noise signal NS, a reference signal is generated containing noise with invariant amplitude properties. By calculating the ratio between the WFF of the myoelectric signal Scm and the WFF of the reference signal Sref, a good quantification of the changes in amplitude of the quasi noise source NSQcan be made. 10 In a second preferred embodiment of the digital signal processing method according to the invention the following steps are further taken: c1) generating a second intermediate signal Si2, which second intermediate signal Si2 is generated by filtering the myoelectric signal Scm> which filtering is done by: moving root mean square filter means with a time window of seconds when the first 15 intermediate signal Sm is generated by moving absolute mean filter means, or moving absolute mean filter means with a time window of seconds when the first intermediate signal Sm is generated by moving root mean square filter means. c2) generating a third intermediate signal Si3, which third intermediate signal Si3 is generated by filtering the reference signal Sref, which filtering is done by: 20 moving root mean square filter means with a time window of Tf3 seconds when the first intermediate signal Sm is generated by moving absolute mean filter means, or moving absolute mean filter means with a time window of Tf3 seconds when the first intermediate signal Sm is generated by moving root mean square filter means, in step d) the ratio is calculated by dividing the second intermediate signal Si2by the third 25 intermediate signal Si3.
When the random noise is modulated by one of the two terms of the WFF equation, the second term may be used to show the deviation of the EMG amplitude properties from the amplitude properties of random noise. The filtering in step b) is preferably performed by an absolute mean filter, therefore enabling the calculation of the RMS ratio of the neural drive of 30 the muscle and modeled random noise for signaling the deviation of the EMG from the noise, where the later may be seen as the norm. The basal properties of a random noise source may be considered to be more or less constant with a WFF of 1.24.
The WFF of the second intermediate signal Si2can be expressed as:
S i2RMS
35 WFF/2 = _ \Si2\Mean 4
The WFF of the third intermediate signal Si3 can be expressed as:
SaRMS
WFFjs =_ 5 | Sj;j |Mean
The ratio can be expressed as: WFF,2 Si2RMS \Si3\Mean 10 _=_*_
WFFi3 \S,-2\Mean Si3RMS
With the above mentioned steps in c1) and c2) either:
15 \Si2\Mean ~ \SJ3\Mean or Sj2rms & Si3RMS
and therefore two variables can be omitted from the ratio, which can therefore be simplified to either: 20 WFFj2 Sj2RMS WFFj2 \ Sj3 \Mean ___«___or___«_ WFFi3 S 13rms WFFj3 \S12\Mean
To eliminate different time delays due to the above mentioned filtering steps and synchronize 25 the envelope of the relevant signals, step c) of the digital signal processing method according to the invention preferably comprises the additional step: c3) delaying signal Si2 by Tdi seconds, such that Tfi+Tf3 is substantially (Te+ Tdi) * 2/3. In a first most preferred embodiment of the digital signal processing method according to the invention step b) comprise the additional steps: 30 b1) generating of a fourth intermediate signal Si4, which fourth intermediate signal S^is generated by filtering the reference signal Sref, which filtering is done by moving root mean square filter means with a time window of Tf4 seconds when the first intermediate signal Sn is generated by root mean square filter means, or moving absolute mean filter means with a time window of Tf4 seconds when the first 35 intermediate signal Sn is generated by moving absolute mean filter means; b2) calculating a quality signal by calculating the difference between the fourth intermediate signal Si4from the first intermediate signal Sn.
5
Essentially the quality signal is test whether the shapes of the fourth intermediate signal Si4and first intermediate signal Snare similar and good results of the quantification of the changes in amplitude of the quasi noise source can be expected.
To eliminate further time delays due to the above mentioned filtering steps in b1) and 5 further synchronize the envelope of the relevant signals, step b1) preferably comprises the additional step b1-1) whereby the first intermediate signal Sn is delayed by Td2 seconds, such that Tfi+Tf4 is substantially (Tf1+Td2) * 2/3.
In a second most preferred embodiment of the digital signal processing method according to the invention step b) comprises the additional step b3), wherein the time window 10 Tfi and Tf4 and the time delay Td2 are controlled such that the difference between the fourth intermediate signal Si4and the first intermediate signal Sn is substantially less than 5%. In that case, the resulting error in the calculation of the abovementioned WFF ratio is kept to an acceptable level.
15 It is also an object of the invention to provide an apparatus which can execute the digital signal processing method according to the invention.
The invention therefore provides an apparatus for processing a composite myoelectric signal Scm, which composite myoelectric signal Scm is measured using passive measuring electrodes applied over the muscle to be measured of a living being, for quantifying changes 20 in amplitude of the composite myoelectric signal Scm, which resembles a quasi noise source NSq, which quasi noise source NSQ represents the firing of motor units of a muscle during muscle contractions and which quasi noise source NSQ has variable amplitude properties, representing variations in muscle force, characterized by, that the apparatus comprises - an external noise source, which has invariant amplitude properties, which noise source is 25 arranged to generate a noise signal NS; - first filtering means for filtering the myoelectric signal Scm! which first filtering means comprises noise filtering means for filtering the quasi noise source NSQ with a time window of Tfi seconds and which first filtering means are arranged to generate a first intermediate signal Sn.
30 - mixing means for mixing the first intermediate signal SM with the noise signal NS, which mixing means are arranged to generate a reference signal Sref.
- comparing means for comparing signal Sref with signal Scm
To execute the first preferred embodiment of the digital signal processing method according to the invention, the 35 - first filtering means comprises either first moving absolute mean filter means or first root mean square (RMS) filter means.
6 - mixing means comprises multiplying means for multiplying the first intermediate signal Sm with the noise signal NS.
- comparing means comprises calculation means for calculation of a ratio or a derivate thereof between the RMS of the myoelectric signal Scm and the RMS of the reference signal 5 Sref or the absolute moving average of the myoelectric signal Scm and the absolute moving average of the reference signal Sref, wherein the ratio quantifies the changes in the statistical properties of the quasi noise source NSQ.
To execute the second preferred embodiment of the digital signal processing method according to the invention, the apparatus comprises second filtering means for filtering the 10 myoelectric signal Scm which second filtering means comprises second moving root mean square filter means with a time window of seconds when the first intermediate signal SM is generated by first moving absolute mean filter means, or second absolute mean filter means with a time window of seconds when the first intermediate signal SM is generated by first moving root mean square filter means and which second filtering means generate a second 15 intermediate signal Si2; third filtering means for filtering the reference signal Sref which third filtering means comprises third moving root mean square filter means with a time window of Tra seconds when the first intermediate signal Sm is generated by first moving absolute mean filter means, or third moving absolute mean filter means with a time window of Tf3 seconds when the first intermediate signal Sm is generated by first moving root mean square filter 20 means and which third filtering means are arranged to generate a third intermediate signal Si3; calculation means for calculating the ratio by dividing the second intermediate signal Si2 by the third intermediate signal S».
Preferable, the apparatus comprises delaying means for delaying signal Si2 by Tdi seconds, such that Tfi+Tra is substantially (Tf2+ Tdi) * 2/3 to eliminate overall timing delays 25 due to the introduced filters.
To execute the first most preferred embodiment of the digital signal processing method according to the invention, the apparatus comprises fourth filtering means for filtering the reference signal Sref which fourth filtering means comprises fourth moving root mean square filter means with a time window of Tf2 seconds when the first intermediate signal SM is 30 generated by first moving absolute mean filter means, or second absolute mean filter means with a time window of Te seconds when the first intermediate signal SM is generated by first moving root mean square filter means and which fourth filtering means are arranged to generate a fourth intermediate signal S*; difference calculation means for calculating the difference between the fourth intermediate signal Sm and the first intermediate signal Sm 35 which difference calculation means are arranged to generate a quality signal.
Preferable, the apparatus comprises delaying means for delaying the first intermediate signal SM by Td2 seconds, such that Tf1+Tf4 is substantially (Tf1+ Td2) * 2/3 to 7 eliminate overall timing delays due to the introduced filters.
To execute the second most preferred embodiment of the digital signal processing method according to the invention the apparatus comprises controlling means for controlling the time window Tf1and Tf4 and the time delay Td2 such that the difference between the fourth 5 intermediate signal Si4and the first intermediate signal Sn is substantially less than 5%.
In general, the quasi noise has substantially similar amplitude properties as white noise. The external noise source NS of the apparatus according to the invention preferably is therefore arranged to generate white noise.
In order to further shape the frequency envelope to the frequency envelope of the 10 quasi noise source the apparatus comprises low pass filtering means for filtering the noise signal NS before it is passed to the multiplying means..
The invention is further elucidated by the following figures wherein:
Figure 1 shows the amplitude histogram of the electrical activity of fatique muscles.
15 Figure 2 shows a preferred embodiment of the apparatus according to the invention.
Figure 3 shows an example of the input signal, intermediate signal, quality signal and ratio.
Figure 4 shows a most preferred embodiment of the apparatus according to the invention.
20
Figure 1 shows the amplitude histogram of the electrical activity of fatigue muscles, at the abscissa the amplitude and at the ordinate the frequency of occurrence. M2 represents the amplitude histogram of random noise, M1 that of fatigued EMG. M3 shows the difference between M1 and M2.
25
Figure 2 shows a preferred embodiment of the apparatus according to the invention, where the following components are used: A Noise Source 30 C | Average | Filter with time window of T seconds D RMS Filter with time window of T seconds E | Average | Filter with time window of T seconds F Delay of 0.5 T seconds G Delay of 0.5 T seconds 35 H RMS Filter with time window of T seconds EXG EXG sub device 8
The circled numbers indicate the measured signals, which are presented in figure 3.
The myoelectrical or EMG signal Scm, see signal 1 in figure 3, which is in this example a respiratory EMG signal, is preprocessed by means of an EXG sub device. From this sub 5 device the signal is divided into two branches of which one branch leads to the first filtering means C, e.g. an Absolute EMG Averager, comprising a box car Averager with an integrating time window of T seconds. From these first filtering means, the first intermediate signal SM is branched to an input of the mixing means, e.g. a multiplier, which multiplies the first intermediate signal SM with a noise signal coming from the noise source A, which is 10 multiplied by a setpoint S with a value of 1. The multiplier outputs the reference signal Sref. The first intermediate signal Sm is also delayed by a DELAY device F, delaying the signal by 0.5T seconds resulting in signal (4) in figure 3.
The reference signal Sref is then fed to 4th filtering means E, e.g. an Absolute noise Averager preferably comprising the same characteristics as the said Absolute EMG Averager C. For 15 testing whether the shapes of the Signals (3) and (4) are similar, they are subtracted leading to signal Q. The difference between the two signals (3) and (4) should be less than 5%.
Now two signal sources are present with similar absolute mean shapes, that of the EMG signal with variable amplitude properties Scm and that of a noise signal with invariant amplitude properties Sref. The equations of the Form Factors for EMG and noise now 20 comprise the same or at least a similar denominator within 5% accuracy. By calculating the ratio of the RMS of Scm and the RMS of Sref we obtain a quantitative measure of the amplitude properties of the EMG signal without the disturbing shape of the massive undulations caused by movements of the muscle.
The EMG signal from the said EXG sub device is connected to an 2nd filters means D, 25 comprising a box car RMS Averager with an integrating window of said T seconds, delayed for 0.5T seconds by delaying means G and connected to one input of the divider means. The output of the said multiplier carrying signal Sref is connected to the denominator input of said divider means via a 3rd filter means H, which is a RMS filtering device similar to D. The resulting output signal of the said divider module, named R, being the quotient of the EMG 30 RMS and the Noise RMS shows the deviation of the EMG’s amplitude properties relative to the predicted norm. When multiplied by 100 this quotient signals the percentage of deviation (9).
Figure 3 shows an example of the input signal, intermediate signal, quality signal and ratio, which are discussed in figure 2.
Figure 4 shows a most preferred embodiment of the apparatus according to the invention, where components A, C,D,E,F,G,H corresponds to equal components as in figure 35 9 2. In this embodiment the quality signal Q is amplified by feedback gain I and fed back via a feedback loop to adjust the noise signal A. An offset to this feedback signal can be applied through setpoint noise gain S. By using this feedback loop the quality signal can be enhanced to 0.5% instead of 5% (see figure 2). During start-up the feedback loop should be 5 disabled during the Filter time constant (60 s). The noise gain (1 to 2) depends of the type of noise used. Gain of 2 for quasi-white noise and 1 for Gaussian noise.
After closing the loop the maximum difference error should be less than 0.5 %.
The method and apparatus according to the invention can be used for example for: 10 Striated muscles (EMG):
Muscle fatigue Abnormal muscle control Spasticity
Multiple innervations 15 - Weaning of ventilators
Muscle revalidation Sports medicine
Smooth muscles (sEMG): 20 - Uterus contractions
Bladder activity Intestines activity
Brain activity (EEG): 25 - Expectancy waves
Epileptic seizures Abnormal brain activity Tracé Alternant in neonates Brain maturation in prematures 30
It is known to those skilled in the art that the above mentioned apparatus or digital signal processing method can be implemented by using a computer or by using one of more dedicated DSP processors.
35

Claims (20)

55 1. Digitale signaalverwerkingsmethode voor het verwerken van een samengesteld myoelektrisch signaal Scm, welk samengesteld myoelektrisch signaal Scm is gemeten middels passieve meetelektroden die zijn aangebracht op een te meten spier van een levend wezen, voor het kwantificeren van veranderingen in amplitude van het 10 myoelektrisch signaal Scm, dat lijkt op een quasi ruisbron NSq, welke quasi ruisbron NSq het afvuren vertegenwoordigt van motoreenheden van een spier tijdens spiersamentrekkingen en welke quasi ruisbron NSq variabele amplitude eigenschappen heeft, die variaties in spierkracht vertegenwoordigen, met het kenmerk, dat de methode de volgende stappen omvat: 15 a) het genereren van een ruissignaal NS vanuit een externe ruisbron, die invariante amplitude eigenschappen heeft; b) het filteren van het myoelektrisch signaal Scm, dat is uitgevoerd door filtermiddelen voor het filteren van de quasi ruisbron NSQ met een tijdframe van Tf1 seconden en welke filtermiddelen een eerste intermediair signaal Sm genereren; 20 c) het mixen van het eerste intermediair signaal Sn met het ruissignaal NS, waarbij het mixen een referentiesignaal Sref genereert; d) het kwantificeren van veranderingen in de statistische eigenschappen van de quasi ruisbron NSq door het vergelijken van signaal Srefmet signaal Scm-1. Digital signal processing method for processing a composite myoelectric signal Scm, which composite myoelectric signal Scm is measured by passive measuring electrodes mounted on a muscle of a living being to be measured, for quantifying changes in amplitude of the myoelectric signal Scm resembling a quasi noise source NSq, which quasi noise source NSq represents firing of motor units of a muscle during muscle contractions and which quasi noise source NSq has variable amplitude properties, representing variations in muscle strength, characterized in that the method comprises the following steps A) generating a noise signal NS from an external noise source, which has invariant amplitude characteristics; b) filtering the myoelectric signal Scm, which is implemented by filtering means for filtering the quasi-noise source NSQ with a time frame of Tf1 seconds and which filtering means generate a first intermediate signal Sm; C) mixing the first intermediate signal Sn with the noise signal NS, the mixing generating a reference signal Sref; d) quantifying changes in the statistical properties of the quasi noise source NSq by comparing signal Sref with signal Scm 2. Digitale signaalverwerkingsmethode volgens conclusie 1, waarin in stap b) het filteren is uitgevoerd door “moving absolute mean” filtermiddelen danwel door “root mean square (RMS)” filtermiddelen. in stap c) het eerste intermediair signaal Sn wordt vermenigvuldigd met het ruissignaal NS, waarbij het vermenigvuldigen een referentiesignaal Sref genereert. 30 in stap d) een ratio of een afgeleide daarvan wordt berekend tussen de RMS van het myoelektrisch signaal Scm en de RMS van het referentiesignaal Sref danwel tussen de “moving absolute mean” van het myoelektrisch signaal Scm en het “moving absolute mean” van het referentiesignaal Sref, waarbij de ratio de veranderingen in amplitude kwantificeert van de quasi ruisbron NSQ. 35Digital signal processing method according to claim 1, wherein in step b) the filtering is performed by moving absolute mean filtering means or by root mean square (RMS) filtering means. in step c) the first intermediate signal Sn is multiplied by the noise signal NS, the multiplication generating a reference signal Sref. In step d) a ratio or a derivative thereof is calculated between the RMS of the myoelectric signal Scm and the RMS of the reference signal Sref or between the "moving absolute mean" of the myoelectric signal Scm and the "moving absolute mean" of the reference signal Sref, the ratio quantifying the changes in amplitude of the quasi-noise source NSQ. 35 3. Digitale signaalverwerkingsmethode volgens conclusie 2, waarbij stap c) de additionele stappen omvat: c1) het genereren van een tweede intermediair signaal Si2, welk tweede intermediair 5 signaal Si2 wordt gegenereerd door het filteren van het myoelektrisch signaal Scm, waarbij het filteren wordt gedaan door: “moving root mean square” filtermiddelen met een tijdsframe van Tf2 seconden als het eerste intermediair signaal Sn wordt gegenereerd door “moving absolute mean” filtermiddelen, of “moving absolute mean” filtermiddelen met een tijdsframe van Tf2 10 seconden als het eerste intermediair signaal Sn is gegenereerd door “moving root mean square” filtermiddelen; c2) het genereren van een derde intermediair signaal Si3, welk derde intermediair signaal Si3 wordt gegenereerd door het filteren van het referentiesignaal Sref, waarbij het filteren wordt gedaan door: 15 “moving root mean square” filtermiddelen met een tijdsframe van Tf3 seconden als het eerste intermediair signaal Sn wordt gegenereerd door “moving absolute mean” filtermiddelen, of “moving absolute mean” filtermiddelen met een tijdsframe van Tf3 seconden als het eerste intermediair signaal Sn wordt gegenereerd door “moving root mean square” filtermiddelen. 20 in stap d) de ratio wordt berekend door het delen van het tweede intermediair signaal Si2door het derde intermediair signaal Si3;3. Digital signal processing method according to claim 2, wherein step c) comprises the additional steps: c1) generating a second intermediate signal Si2, which second intermediate signal Si2 is generated by filtering the myoelectric signal Scm, the filtering being done by: "moving root mean square" filter means with a time frame of Tf2 seconds if the first intermediate signal Sn is generated by "moving absolute mean" filter means, or "moving absolute mean" filter means with a time frame of Tf2 10 seconds as the first intermediate signal Sn is generated by moving root mean square filtering means; c2) generating a third intermediate signal Si3, which third intermediate signal Si3 is generated by filtering the reference signal Sref, the filtering being done by: moving root mean square filtering means with a time frame of Tf3 seconds as the first intermediate signal Sn is generated by moving absolute mean filtering means, or moving absolute mean filtering means with a time frame of Tf3 seconds when the first intermediate signal Sn is generated by moving root mean square filtering means. In step d) the ratio is calculated by dividing the second intermediate signal Si2 by the third intermediate signal Si3; 4. Digitale signaalverwerkingsmethode volgens conclusie 3, waarbij stap c) de additionele stap omvat: 25 c3) het vertragen van signaal Si2 met Td1 seconden, zodanig dat Tf1+Tf3 in hoofdzaak (Tf2+ Td1) * 2/3 bedraagt.The digital signal processing method according to claim 3, wherein step c) comprises the additional step: c3) delaying signal Si2 by Td1 seconds, such that Tf1 + Tf3 is substantially (Tf2 + Td1) * 2/3. 5. Digitale signaalverwerkingsmethode volgens conclusie 3 of 4, waarbij stap b) de additionele stappen omvat: 30 b1) het genereren van een vierde intermediair signaal Si4, welk vierde intermediair signaal Si4 wordt gegenereerd door het filteren van het referentiesignaal Sref, waarbij het filteren wordt gedaan door “moving root mean square” filtermiddelen met een tijdsframe van Tf4 seconden als het eerste intermediair signaal Sn wordt gegenereerd door “root mean square” filtermiddelen, of “moving absolute mean” filtermiddelen met 35 een tijdsframe van Tf4 seconden als het eerste intermediair signaal Sn wordt gegenereerd door “moving absolute mean” filtermiddelen; b2) het berekenen van een kwaliteitssignaal door het berekenen van het verschil tussen het vierde intermediair signaal Si4en het eerste intermediair signaal Sm-5. Digital signal processing method according to claim 3 or 4, wherein step b) comprises the additional steps: b1) generating a fourth intermediate signal Si4, which fourth intermediate signal Si4 is generated by filtering the reference signal Sref, thereby filtering done by "moving root mean square" filter means with a time frame of Tf4 seconds if the first intermediate signal Sn is generated by "root mean square" filter means, or "moving absolute mean" filter means with a time frame of Tf4 seconds as the first intermediate signal Sn is generated by "moving absolute mean" filter means; b2) calculating a quality signal by calculating the difference between the fourth intermediate signal Si4 and the first intermediate signal S 6. Digitale signaalverwerkingsmethode volgens conclusie 5, waarbij stap b1) de additionele tussenstap omvat: 5 b1 -1) het vertragen van het eerste intermediair signaal Sm met Td2 seconden, zodanig dat Tfi+Tf4 in hoofdzaak (Tfi+Td2) * 2/3 bedraagt.The digital signal processing method according to claim 5, wherein step b1) comprises the additional intermediate step: 5 b1 -1) delaying the first intermediate signal Sm by Td2 seconds, such that Tfi + Tf4 substantially (Tfi + Td2) * 2/3 amounts. 7. Digitale signaalverwerkingsmethode volgens conclusie 5 of 6, waarbij stap b) de additionele stap omvat: 10 b3) het sturen van het tijdsframe Tfi en Tf4 en de tijdsvertraging Td2zodanig dat het verschil tussen het vierde intermediair signaal Si4en het eerste intermediair signaal SM in hoofdzaak minder dan 5% bedraagt.Digital signal processing method according to claim 5 or 6, wherein step b) comprises the additional step: b3) controlling the time frame Tf1 and Tf4 and the time delay Td2 such that the difference between the fourth intermediate signal Si4 and the first intermediate signal SM less than 5%. 8. Digitale signaalverwerkingsmethode volgens conclusie 5 of 6, waarbij stap b) de 15 additionele stappen omvat: b4) het versterken van het kwaliteitssignaal zoals berekend in stap b2); b5) het toepassen van een offset op het versterkte kwaliteitssignaal van stap b4); b6) het vermenigvuldigen van het ruissignaal NS met het signaal van stap b5) en in stap c) 20 het eerste intermediair signaal Sm wordt vermenigvuldigd met het signaal van stap b5), waarbij het vermenigvuldigen een referentiesignaal Sref genereert.8. Digital signal processing method according to claim 5 or 6, wherein step b) comprises the additional steps: b4) amplifying the quality signal as calculated in step b2); b5) applying an offset to the amplified quality signal from step b4); b6) multiplying the noise signal NS by the signal from step b5) and in step c) the first intermediate signal Sm is multiplied by the signal from step b5), the multiplication generating a reference signal Sref. 9. Digitale signaalverwerkingsmethode volgens 8, waarbij stap b3) de stap omvat: b3) het sturen van de tijdsframe Tn en Tf4 en de tijdsvertraging Td2zodanig dat het 25 verschil tussen het vierde intermediair signaal Si4en het eerste intermediair signaal Sm in hoofdzaak minder dan 0.5% bedraagt.9. Digital signal processing method according to 8, wherein step b3) comprises the step of: b3) controlling the time frame Tn and Tf4 and the time delay Td2 such that the difference between the fourth intermediate signal Si4 and the first intermediate signal Sm is substantially less than 0.5% amounts. 10. Inrichting voor het verwerken van een samengesteld myoelektrisch signaal Scm, welk samengesteld myoelektrisch signaal Scm is gemeten middels passieve 30 meetelektroden die zijn aangebracht op een te meten spier van een levend wezen, voor het kwantificeren van veranderingen in amplitude van het myoelektrisch signaal Scm, dat lijkt op een quasi ruisbron NSQ, welke quasi ruisbron NSQ het afvuren vertegenwoordigd van motoreenheden van een spier tijdens spiersamentrekkingen en welke quasi ruisbron NSQ variabele amplitude eigenschappen heeft, die variaties 35 in spierkracht vertegenwoordigen, met het kenmerk, dat de inrichting omvat: - een externe ruisbron, die in hoofdzaak gelijke amplitude eigenschappen heeft als de quasi ruisbron en invariante amplitude eigenschappen heeft, welke ruisbron is ingericht voor het genereren van een ruissignaal NS; - eerste filtermiddelen voor het filteren van het myoelektrisch signaal Scm, welke eerste filtermiddelen ruisfiltermiddelen omvat voor het filteren van de quasi ruisbron NSq met een tijdsframe van Tf1 seconden en welk eerste filtermiddelen zijn ingericht 5 voor het genereren van een eerste intermediair signaal Sn. - mixmiddelen voor het mixen van het eerste intermediair signaal Sm met het ruissignaal NS, welke mixmiddelen zijn ingericht voor het genereren van een referentiesignaal Sref. - vergelijkingsmiddelen voor het vergelijken van het signaal Sref met signaal Scm 1010. Device for processing a composite myoelectric signal Scm, which composite myoelectric signal Scm is measured by passive measuring electrodes mounted on a muscle of a living being to be measured, for quantifying changes in amplitude of the myoelectric signal Scm, resembling a quasi noise source NSQ, which quasi noise source NSQ represents firing of motor units of a muscle during muscle contractions and which quasi noise source NSQ has variable amplitude properties, representing variations in muscle force, characterized in that the device comprises: external noise source, which has substantially the same amplitude characteristics as the quasi noise source and has invariant amplitude characteristics, which noise source is adapted to generate a noise signal NS; - first filtering means for filtering the myoelectric signal Scm, which first filtering means comprises noise filtering means for filtering the quasi-noise source NSq with a time frame of Tf1 seconds and which first filtering means are adapted to generate a first intermediate signal Sn. - mixing means for mixing the first intermediate signal Sm with the noise signal NS, which mixing means are adapted to generate a reference signal Sref. - comparing means for comparing the signal Sref with signal Scm 10 11. Inrichting volgens conclusie 10, waarin de - eerste filtermiddelen eerste “moving absolute mean” filtermiddelen danwel eerste “root mean square (RMS)” filtermiddelen omvatten. 15. mixmiddelen vermenigvuldigingsmiddelen voor het vermenigvuldigen van het eerste intermediaire signaal Sn met het ruissignaal NS omvatten. - vergelijkingsmiddelen berekeningsmiddelen omvatten voor het berekenen van een ratio of een afgeleide daarvan tussen de RSM van het myoelectric signaal Scm en de RMS van het referentiesignaal Sref danwel tussen het “absolute moving average” van 20 het myoelektrische signaal Scm en het “absolute moving average” van het referentiesignaal Sref, waarin de ratio veranderingen van de statistische eigenschappen van de quasi ruisbron NSq kwantificeert.Device as claimed in claim 10, wherein the first filter means comprise first moving absolute mean filter means or first root mean square (RMS) filter means. 15. Mixing means comprise multiplying means for multiplying the first intermediate signal Sn with the noise signal NS. - comparing means comprise calculating means for calculating a ratio or a derivative thereof between the RSM of the myoelectric signal Scm and the RMS of the reference signal Sref or between the "absolute moving average" of the myoelectric signal Scm and the "absolute moving average" of the reference signal Sref, in which the ratio quantifies changes in the statistical properties of the quasi-noise source NSq. 12. Inrichting volgens conclusie 11, waarin de inrichting omvat: tweede filtermiddelen voor het filteren van het myoelektrische signaal Scm omvattende tweede “moving root mean square” filtermiddelen met een tijdsframe van Tf2 seconden als het eerste intermediaire signaal Sm is gegenereerd door eerste “moving absolute mean” filtermiddelen, of 30 tweede “absolute mean” filtermiddelen met een tijdsframe van Tf2 seconden als het eerste intermediaire signaal Sm is gegenereerd door eerste “moving root mean square” filtermiddelen en welke tweede filtermiddelen een tweede intermediaire signaal Si2 genereert; derde filtermiddelen voor het filteren van het referentiesignaal Sref omvattende derde 35 “moving root mean square” filtermiddelen met een tijdsframe van Tfs seconden als het eerste intermediaire signaal SM is gegenereerd door eerste “moving absolute mean” filtermiddelen, of derde “moving absolute mean” filtermiddelen met een tijdsframe van Tf3 seconden als het eerste intermediaire signaal Sn is gegenereerd door eerste “moving root mean square” filtermiddelen en welke derde filtermiddelen zijn ingericht voor het genereren van een derde 5 intermediaire signaal Si3; berekeningsmiddelen voor het berekenen van de ratio door het delen van het tweede intermediaire signaal Si2door het derde intermediaire signaal Si3.12. Device as claimed in claim 11, wherein the device comprises: second filtering means for filtering the myoelectric signal Scm comprising second moving root mean square filtering means with a time frame of Tf2 seconds when the first intermediate signal Sm is generated by first moving absolute mean filtering means, or second absolute mean filtering means with a time frame of Tf2 seconds if the first intermediate signal Sm is generated by first moving root mean square filtering means and which second filtering means generates a second intermediate signal Si2; third filtering means for filtering the reference signal Sref comprising third moving root mean square filtering means with a time frame of Tfs seconds when the first intermediate signal SM is generated by first moving absolute mean filtering means, or third moving absolute mean filtering means with a time frame of Tf3 seconds when the first intermediate signal Sn is generated by first moving root mean square filtering means and which third filtering means are adapted to generate a third intermediate signal Si3; calculating means for calculating the ratio by dividing the second intermediate signal Si2 by the third intermediate signal Si3. 13. Inrichting volgens conclusie 12, waarin de inrichting vertragingsmiddelen omvat voor 10 het vertragen van het signaal Si2 met Td1 seconden, zodanig dat Tf1+Tf3 in hoofdzaak (Tf2+ Tdi) * 2/3 bedraagt.13. Device as claimed in claim 12, wherein the device comprises delaying means for delaying the signal Si2 by Td1 seconds, such that Tf1 + Tf3 is substantially (Tf2 + Tdi) * 2/3. 14. Inrichting volgens conclusie 12 of 13, waarin de inrichting omvat: vierde filtermiddelen voor het filtering van het referentiesignaal Sref welke vierde 15 filtermiddelen vierde “moving root mean square” filtermiddelen omvatten met een tijdsframe van Tf2 seconden als het eerste intermediaire signaal Sm is gegeneerd door de eerste “moving absolute mean” filtermiddelen, of tweede “absolute mean” filtermiddelen omvatten met een tijdsframe van Tf2 seconden als het eerste intermediaire signaal Sm is gegeneerd door de eerste “moving root 20 mean square” filtermiddelen en welke vierde filtermiddelen zijn ingericht voor het genereren van een vierde intermediaire signaal Si4; verschilberekeningsmiddelen voor het berekenen van het verschil tussen het vierde intermediaire signaal Si4en het eerste intermediaire signaal Sm, welke 25 verschilberekeningsmiddelen zijn ingericht voor het genereren van een kwaliteitssignaal.14. Device as claimed in claim 12 or 13, wherein the device comprises: fourth filtering means for filtering the reference signal Sref, which fourth filtering means comprise fourth moving root mean square filtering means with a time frame of Tf2 seconds when the first intermediate signal Sm is generated by the first moving absolute mean filtering means, or second "absolute mean" filtering means having a time frame of Tf2 seconds when the first intermediate signal Sm is generated by the first moving root mean square filtering means and which fourth filtering means are arranged for generating a fourth intermediate signal Si 4; difference calculating means for calculating the difference between the fourth intermediate signal Si4 and the first intermediate signal Sm, which difference calculating means are adapted to generate a quality signal. 15. Inrichting volgens conclusie 14, waarin de inrichting vertragingsmiddelen omvat voor het vertragen van het eerste intermediaire signaal Sm met Td2 seconden, zodanig dat15. Device as claimed in claim 14, wherein the device comprises delaying means for delaying the first intermediate signal Sm by Td2 seconds, such that 30 Tf1+Tf4 in hoofdzaak (Tfi+Td2) * 2/3 bedraagt.Tf1 + Tf4 is essentially (Tf1 + Td2) * 2/3. 16. Inrichting volgens conclusie 14 of 15, waarin de inrichting stuurmiddelen omvat voor het sturen van het tijdsframeTn en Tf4 en de tijdsvertraging Td2zodanig dat het verschil tussen het vierde intermediaire signaal Si4en het eerste intermediaire signaalDevice as claimed in claim 14 or 15, wherein the device comprises control means for controlling the time frame Tn and Tf4 and the time delay Td2 such that the difference between the fourth intermediate signal Si4 and the first intermediate signal 35 Sm in hoofdzaak minder dan 5% bedraagt.35 Sm is substantially less than 5%. 17. Inrichting volgens conclusie 14 of 15, waarin de inrichting versterkingsmiddelen omvat voor het versterken van het kwaliteitssignaal voor het genereren van signaal Qa, offsetmiddelen voor het toepassen van een offset op signaal Qa, 5 vermenigvuldigingsmiddelen voor het vermenigvuldigen van ruissignaal NS met signaal Qam, en het eerste intermediaire signaal Sn is vermenigvuldigd met het signaal Qam, waarin het vermenigvuldigen een referentiesignaal Sref genereert.17. Device as claimed in claim 14 or 15, wherein the device comprises amplifying means for amplifying the quality signal for generating signal Qa, offset means for applying an offset to signal Qa, multiplication means for multiplying noise signal NS with signal Qam, and the first intermediate signal Sn is multiplied by the signal Qam, wherein the multiplication generates a reference signal Sref. 18. Inrichting volgens conclusie 17, waarin de inrichting stuurmiddelen omvat voor het sturen van het tijdsframeTf1 en Tf4 en de tijdsvertraging ïd2zodanig dat het verschil tussen het vierde intermediaire signaal Si4en het eerste intermediaire signaal SM in hoofdzaak minder dan 0.5% bedraagt.The device of claim 17, wherein the device comprises control means for controlling the time frame Tf1 and Tf4 and the time delay such that the difference between the fourth intermediate signal Si4 and the first intermediate signal SM is substantially less than 0.5%. 19. Inrichting volgens conclusies 10 tot en met 18, waarin de externe ruisbron is ingericht voor het genereren van Gaussische ruis.The device according to claims 10 to 18, wherein the external noise source is adapted to generate Gaussian noise. 20. Inrichting volgens conclusies 10 tot en met 19, waarin de inrichting laagdoorlaat filtermiddelen omvat voor het filteren van het ruissignaal NS voordat het ruissignaal 20 NS is doorgegeven aan de vermenigvuldigingsmiddelen.20. Device as claimed in claims 10 to 19, wherein the device comprises low-pass filtering means for filtering the noise signal NS before the noise signal NS is passed to the multiplication means.
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