Note: Descriptions are shown in the official language in which they were submitted.
CA 02264112 1999-02-15Triggering of a Measurement Method for the QualityAssessment of Audio and/or speech signalsField of the LgventionThe present invention refers to the quality assessment ofdata-reduced audio and/or speech signals and in particularto a method and an apparatus for triggering a measurementmethod for the quality assessment of audio and/or speechsignals.Background of the Invention and Description of Prior ArtModern methods for the quality assessment of data-reducedaudio and/or speech signals, such as e.g. NMR, PAQM or POMsignals, do not employ any special, synthetically generatedmeasurement signals, but genuine audio and/or speech signalsfor the purpose of measurement. This means that the originalsignal and the signal to be assessed must be available forthe measurement, i.e. for the quality assessment of audioand/or speech signals. The original signal is e.g. an audioand/or speech signal recorded in a sound studio that is tobe transmitted to a receiver by means of a cable connectionor by means of a wireless radio path. For economicaltransmission this signal must be data-reduced or coded,after which the signal is sent as a bit stream to a digitaltransmitter, which performs e.g. a pulse amplitudequadrature modulation, whereby the data-reduced audio and/orspeech signal, i.e. the bit stream, is modulated onto acarrier. In the case of a wireless radio transmission thiscarrier is radiated by a suitable antenna and is receivedand demodulated by a suitable receiving antenna. After thedemodulation of the bit stream which has been modulated bymeans of E1 suitable modulation method, this resembles thebit stream present in the- transmitter prior to theCA 02264112 1999-02-15modulation, apart from the influences of the radio path.After an inverse coding or decoding and after adigital/analog conversion, the signal originally recorded inthe sound studio can be rendered audible again.Methods for the quality assessment of dataâreduced audiosignals identify differences in the audio signal madeaudible in the receiver compared to the audio signalrecorded, in the present example, in the sound studio, so asto detect either coding/decoding errors or bit errors whichhave been introduced by the radio path. A reference signal,i.e. the signal recorded in the sound studio, is comparedwith a âtest signal, i.e. the signal. made audible in thereceiver after the digital/analog conversion, in order toassess the quality of the coding, the radio path and thedecoding.As has already been noted, the reference signal and the testsignal must be present for the measurement. The delaybetween these two signals must be less than 500 ms forcurrent measurement methods. This presents no problem underlaboratory conditions, for which reason the qualityassessment of data-reduced audio and/or speech signals isalready performed under laboratory conditions.However, if field measurements are to be performed, there isnormally no reference signal available, since the signalsource, i.e. the sound studio or a transmitting antenna, isphysically located far away from a measurement point.It is obvious that for the quality assessment of audiosignals the reference signal on which the test signal isbased must be known. Since the quality assessment does notrequire that the test signal be compared continuously withthe reference signal, it is possible, assuming that thecoding or decoding and the radio path do not change toostrongly with time, to compare just a section of the testCA 02264112 1999-02-15signal, which is based on a reference signal, with thereference signal. Obviously this section of the test signalwhich is based on the reference signal and the referencesignal itself must be present in the measurement device.Radio programme audio signals which return time after timein the same form are e.g. jingles, which introduce certainradio programmes and remain unchanged over long periods oftime since they contribute greatly to the identification ofa listener with "his" radio programme. This means that if ajingle is provided once at the transmitter it is possible toperform qualityâ measurements on a received audio and/orspeech signal at many differnt places and at many differenttimes.Methods for recognizing jingles are also already known.However, these methods serve only to recognize a particularpiece of music, e.g for questionnaire purposes or forsupervising the correct charging of radiotransmitters, wherethe same serve merely to recognize whether a particularpiece of music has been played or not. These known methodsfor jingle recognition supply a measure for the agreementwith a particular signal only at the end of the jingle. Thisoutcome is useless for a measurement method for the qualityassessment of audio and/or speech signals, however, sincethe measurement period has already been concluded when thejingle has been recognized. Equally, an exact compensationof the delay between the test signal and the referencesignal is not possible in the known methods for jinglerecognition.Summary of the InventionIt is the object of the present invention to provide anexact triggering of a measurement method for the qualityassessment of audio and/or speech signals.CA 02264112 1999-02-15In accordance with a first aspect of the present inventionthis object is achieved by a method of triggering ameasurement method for the quality assessment of audioand/or speech signals, comprising the steps of providingdigital values of a reference signal which forms the basisfor at least a part of a test signal the quality of which isto be assessed; storing digital values of the test signal atleast temporarily; determining the degree of agreementbetween a section of the values of the reference signal andthe values of the test signal; and triggering themeasurement method as soon as a specified degree ofagreement is exceeded.In accordance with a second aspect of the present inventionthis object is achieved by an apparatus for triggering ameasurement device which implements a measurement method forthe quality assessment of audio and/or speech signals,comprising a first storage device for storing digital valuesof a reference signal which forms the basis for at least apart of a test signal the quality of which is to beassessed; a second storage device for storing digital valuesof the test signal at least temporarily; a device fordetermining the degree of agreement between a section of thevalues of the reference signal and the values of the testsignal; a triggering device for triggering the measurementmethod executed in the measurement device as soon as aspecified degree of agreement is exceeded.The present invention is based on the fact that a jinglebefore a radio transmission is particularly suitable forincorporation in the quality assessment of the radio signal.The prerequisite for this is that such a jingle istransmitted during the measurement period. The referencesignal, i.e. the jingle prior to coding and transmission,can be recorded at the transmitter before the measurementand then brought to the receiver in one way or another, e.g.via modem or magnetic tape. A jingle detector according toCA 02264112 1999-02-15the present invention continuously compares the receivedsignal with the provided or stored reference signal, only asmall section of the reference signal being compared herewith the test signal in continuous comparison and at leastone other section of the reference signal being comparedhere with the corresponding section of the test signal oncea specified degree of agreement has been reached. As soon asan agreement is recognized, the jingle, i.e. the referencesignal, is played in synchronism with the test signal whichis based on the jingle, since the start of the jingle hasbeen identified, after which any of the known technicalmeasurement methods for comparing the two signals can beused for the quality assessment of the coding, the decoding,the transmission, etc.Brief Description of the DrawingsA. preferred embodiment of the present invention will beexplained in more detail below making reference to theenclosed drawings, in whichFig. 1 shows a system arrangement which can implement thepresent invention; andFig. 2 shows a schematic block circuit diagram of theapparatus for triggering a measurement method forthe quality assessment of audio and/or speechsignals.Detailed Description of a Preferred EmbodimentFig. 1 shows a schematic system arrangement which canimplement the method and the apparatus of the presentinvention. An audio source 10, which may be a sound studioor also a magnetic tape recorded by a sound studio, isCA 02264112 1999-02-15connected to a transmitter 12, which in turn has atransmitting antenna 14 assigned to it. The transmitter 12can perform an analog/digital conversion of the audio and/orspeech signal coming from the audio source 10. The digitalaudio and/or speech signal is also coded in the transmitter12, i.e. it is data-reduced, as is known to persons skilledin the art, and is modulated onto a carrier by means of asuitable modulation method, also known to persons skilled inthe art, so that the coded and modulated audio and/or speechsignal can be radiated over the transmitting antenna 14. Thecoded and modulated audio and/or speech signal propagatesover a radio path 16, to be received by a receiving antenna18. To persons skilled in the art it is obvious that theradio path 16 is merely representative, since the same canequally well be realized by means of a cable connection,which can carry e.g. digital radio signals or also digitaltelevision signals, i.e. multimedia signals.The coded and modulated audio and/or speech signal receivedby the receiving antenna 18 is demodulated and decoded bysuitable means, and is also analog-digital converted, in areceiver 20 and is fed over a receiving line 22 to a jingledetector 24, which constitutes the apparatus for triggeringa measurement method for the quality assessment of audioand/or speech signals and which is connected over a detectorconnection 26 to a measurement device 28 (Fig. 2) which canperform one of a plurality of measurement methods, known topersons skilled in the art, for the quality assessment ofaudio and/or speech signals.A dashed line from the connection of the audio source 10 andthe transmitter 12 to the jingle detector 24 represents areference signal line 30. The dashed representation of thereference signal line 30 is meant to symbolize that thisconnection between the audio source 10 and the jingledetector 24 need not be a continuous connection, since, ashas already been stated, a reference signal, i.e. the audioCA 02264112 1999-02-15signal of a jingle prior to the coding and modulation, needonly be presented to the jingle detector 24 once or atcertain moments in time. In contrast, the unbrokenconnections represent data connections which arecontinuously active, at least during a measurement processfor the quality assessment of audio signals.Fig. 2 shows a detailed representation of the jingledetector 24, which in a preferred embodiment may be apersonal computer with suitable software and with a suitableoperating system. The jingle detector 24 has a storagedevice 242 for storing the reference signal and for storingthe test signal, which is supplied to a digital signalprocessor card 244 via a âtest signal input 22. The testsignal can be supplied as required to the measurement devicevia a first output 26a, while a second output 26b of thedigital signal processor card 244 will supply the referencesignal to the measurement device 28 as required. Acommunication line 26c serves for initialization tasks andfor measurement communications between the jingle detector24 and the measurement device 28. The fact that thecommunication line 26c is dashed shows, analagously to thereference signal line 30 of Fig. 1, that the communicationline 26c is not continuously active but will signal simplye.g. the begin or the end of a measurement by themeasurement device 28.In a preferred embodiment of the method of the presentinvention, the reference signal, which had been transferredfrom the audio source 10 to the jingle detector 24 in somesuitable way, was recorded on the storage device 242, whichis a hard disk of a standard personal computer. Asadditional hardware the standard personal computer alsocontains the digital signal processor card 244 in the formof a plug-in card, which. provides the audio test signalinput 22 and also the first output 26a and the second output26b. It is pointed out here that the three lines 26a to 26c,CA 02264112 1999-02-15as can already be seen from the reference numerals assignedto them, are contained in the detector connection 26 of Fig.1. The test signal input 22 of the signal processor card244, which may contain several signal processors, is, as canbe seen from Fig. 1, suitably connected to the receiver 20.The first output 26a and the second output 26b of thedigital signal processor card 244 are connected tocorresponding inputs of the measurement device 28 for thetest signal and for the reference signal respectively.According to a preferred embodiment of the method of thepresent invention, a first section of the values of thereference signal is read from âthe hard disk 242 into amemory of the digital signal processor card 244 at the startof a measurement. cycle. This first section may be about1.5 s long. In the digital signal processor card 244, thisfirst section of the values of the reference signal isfiltered, undersampled and then compared by means of a crosscorrelation with a section of the test signal treated in thesame way, which has been supplied to the digital signalprocessor card 244 or the storage device 242 over thereceiving line 22. The test signal has also been filteredand undersampled.For persons skilled in the art it is obvious that in thejingle detector 24 an analog/digital conversion of the testsignal can be performed by a suitable section of the digitalsignal processor card 244 if the receiver 20 delivers analogvalues. If the receiver 20 delivers digital values of thetest signal, however, there is no need for an analog/digitalconversion in the jingle detector 24. It is also obviousthat the cross correlation between a section of the valuesof the reference signal and a section of the values of thetest signal is performed in a digital way. In a preferredembodiment the algorithm for performing the crosscorrelation, i.e. the arrangement determining the degree ofagreement of a section of the values of the reference signalCA 02264112 1999-02-15with the values of the test signal, is implemented bysoftware. other than in this embodiment, the arrangementdetermining the degree of agreement of a section of thevalues of the reference signal with the values of the testsignal can also be implemented by hardware using suitableshift registers and logic gates, which will essentiallyperform an exclusive-OR function.As has already been stated, the comparison between a sectionof the values of the reference signal and a section of thevalues of the test signal to be assessed takes place on asection basis. In a preferred embodiment of the presenta section consists of 512 sample values of the"frame". Ifthe section of the values of the reference signal is madeinvention,test signal, this section also being termed ashorter, the comparison operation will execute more quickly,though the number of faulty detections of agreement betweenthe test signal and the reference signal will increase. Ifthe section of the reference signal values which is used todetermine a degree of agreement is chosen to be longer, thetime needed for this operation does indeed increase, but onthe other hand the probability of a faulty detection of anagreement will decrease.If the degree of agreement or âthe degree of correlationthe method ofmeasurement method for the quality assessment of audiosignals establishes that the values of the test signal justcompared with the section of the values of the referenceexceeds a certain value, triggering asignal represent the beginning of a jingle which is presentas reference signal in its original form. If the specifieddegree of agreement or the specified degree of correlationis exceeded, a measurement method for the quality assessmentThe jingle detector 24the the28 over the communication line 26c,signalsthemeasurement deviceof audio is triggered.announces beginning of measurement towhereby the measurement. device 28 is activated so as toCA 02264112 1999-02-15-10-receive a further section of the values of the referencesignal over the first output 26a of the jingle detector 24,the corresponding values of the test signal beingcommunicated to the measurement device over the secondoutput 26b of the jingle detector 24 at essentially the sametime. After triggering the measurement method, which isexecuted by the measurement device 28, further sections ofthe reference signal are read from the hard disk 242 and areoutput, i.e. transmitted to the measurement device 28,together with the test signal received over the receivingline 22. The first output 26a and the second output 26b maybe four-channel audio interfaces or, for stereo outputs, theleft channel and. the right channel of the digital audiosignal. The left channel can then transmit the test signal,which corresponds to the output 26b, whereas the rightchannel, i.e. the output 26a, will communicate the referencesignal from the hard disk 242.Through the correlation of the sections of the values of thetest signal with a corresponding number of values of thereference signal, the delay between the reference signal andthe test signal is automatically removed, since the sectionof the values of the reference signal is compared with thecontinuous bit stream of the received test signal. A newsection of reference signal values which is transmitted fromthe jingle detector to the measurement device corresponds tothe values of the test signal which is based on thereference signal, since transmission of further sections ofthe test signal to the measurement device does not commenceuntil the jingle detector assumes that the current sectionof the test signal values which has just been involved inthe correlation evaluation is that section which is based onthe section of the reference signal values which is used fordetermining the correlation.other than for the jingle detector according to the priorart described above, in an embodiment of the presentCA 02264112 1999-02-15invention the whole jingle apart from the first section ofthe values of the reference signal will be available to themeasurement device for the purposes of quality assessment.In the prior art the whole jingle would first have to havebeen played in order to be able to establish afterwards thatthe test signal concerned was a jingle.Since the correlation of the two signals means that thedelay between them is known, the principle of the methodbeing such that the delay is smaller than a section lengthor frame length, this delay can also be compensated for atthe same time. The first section of the reference signalused by the jingle detector 24 to determine agreement canalso be provided for the measurement method for the qualityassessment of audio signals if both signals are outputsimultaneously by the digital signal processor card.It is pointed out here that for the embodiment described upto now the reference signal on the hard disk 242 is storedpermanently, whereas the test signal for correlation is onlystored temporarily. After agreement between the section ofthe values of the reference signal and values of the testsignal has been established, further received values of thetest signal are not temporarily stored in the jingledetector 24 but are output directly to the measurementdevice 28 over the second output 26b. If the first sectionof the values of the reference signal is also to be used forthe measurement, however, this is only possible if bothsignals are output simultaneously by the digital signalprocessor card 244. If the digital signal processor card 244has sufficient main memory, a longer section of the testsignal can also be stored and delayed in the memory. Whenthe jingle is recognized, the whole jingle and not just thatpart of the jingle which is transmitted after recognitioncan be measured.As has already been observed, this phase constitutes theCA 02264112 1999-02-15_ 12 ..actual measurement phase, which is performed in themeasurement device 28. The only function of the jingledetector 24 in this measurement phase is to communicatefurther sections of the values of the reference signal insynchronism with received values of the test signal to themeasurement device 28. To persons skilled in the art it isobvious that the number of values of a section must be thesame in the test phase for the test signal and the referencesignal. It is also obvious to persons skilled in the artthat the reference signal can consist of any number ofsections, just as the user wishes. The reference signalmust, however, be split into at least two sections, onesection then being used by the jingle detector 24 toestablish agreement between a corresponding section of thetest signal and the first section of the reference signal.The other section is then used by the measurement device 28together with a corresponding section of the test signal forthe quality assessment of the test signal. As has beendescribed above, however, by temporarily storing a longersection of the test signal the first section of thereference signal and the corresponding section of the testsignal can be used for the quality assessment by themeasurement device 28.If, through suitable software in the jingle detector 24, nosignal or a very small signal is output before the start ofthe measurement phase, i.e. the phase of transmitting thetest signal and the reference signal over the outputs 26band 26a, and after this cited phase, the measurement device28 can, in a way which is known to persons skilled in theart, be so programmed that the beginning and the end of themeasurement phase are recognized automatically. Thebeginning and the end of the measurement phase arecommunicated over the communication line 26c from the jingledetector 24 to the measurement device 28.
