AU714063B2

AU714063B2 - Triggering of a measurement method for the quality assessment of audio and/or speech signals

Info

Publication number: AU714063B2
Application number: AU49488/97A
Authority: AU
Inventors: Ernst Eberlein; Heinz Gerhauser; Michael Keyhl; Christian Schmidmer; Bodo Teichmann
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 1996-10-21
Filing date: 1997-10-21
Publication date: 1999-12-16
Anticipated expiration: 2017-10-21
Also published as: EP0891685B1; CA2264112C; JP2000505269A; DE19730716A1; DE59700423D1; DK0891685T3; KR20000048615A; EP0891685A1; AU4948897A; ATE184444T1; WO1998018295A1; KR100319465B1; JP3155283B2

Abstract

A process and device (24) for triggering a measurement process for evaluating the quality of audio and/or speech signals enable field measurements to be carried out to determine the quality of a digital transmission. During a first step, digital values of a reference signal underlying at least part of a test signal whose quality is to be evaluated are stored. Digital values of the test signals are also at least temporarily stored. The degree to which a section of the reference signal values coincides with the test signal values is determined to trigger the measurement process as soon as a predetermined degree of coincidence is exceeded, in order to compare a further section of the reference signal values to the test signal values in the relative position in time of the reference signal and test signal values at the moment when a predetermined degree of coincidence occurs.

Description

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la Triggering of a Measurement Method for the Quality Assessment of Audio and/or Speech Signals Description The present invention refers to the quality assessment of data-reduced audio and/or speech signals and in particular to a method and a device for triggering a measurement method for the quality assessment of audio and/or speech signals.

Modern methods for the quality assessment of data-reduced audio and/or speech signals, such as e.g. NMR, PAQM or POM signals, do not employ any special, synthetically generated measurement signals, but genuine audio and/or speech signals for the purpose of measurement. This means that the original signal and the signal to be assessed must be available for the measurement, i.e. for the quality assessment of audio and/or speech signals. The original signal is e.g. an audio and/or speech signal recorded in a sound studio that is to be transmitted to a receiver by means of a cable connection or by means of a wireless radio path. For economical transmission this signal must be data-reduced or coded, after which the signal is sent as a bit stream to a digital transmitter, which performs e.g. a pulse amplitude quadrature modulation, whereby the data-reduced audio and/or speech signal, i.e. the bit stream, is modulated onto a carrier. In the case of a wireless radio transmission this carrier is radiated by a suitable antenna and is received and demodulated by a suitable receiving antenna. After the demodulation of the bit stream which has been modulated by means of a suitable modulation method, this resembles the bit stream present in the transmitter prior to the modulation, apart from the influences of the radio path.

After an inverse coding or decoding and after a digital/ analog conversion, the signal originally recorded in the sound studio can be rendered audible again.

2 Methods for the quality assessment of data-reduced audio signals identify differences in the audio signal made audible in the receiver compared to the audio signal recorded, in the present example, in the sound studio, so as to detect either coding/decoding errors or bit errors which have been introduced by the radio path. A reference signal, i.e. the signal recorded in the sound studio, is compared with a test signal, i.e. the signal made audible in the receiver after the digital/analog conversion, in order to assess the quality of the coding, the radio path and the decoding.

As has already been noted, the reference signal and the test signal must be present for the measurement. The delay between these two signals must be less than 500 ms for current measurement methods. This presents no problem under laboratory conditions, for which reason the quality assessment of data-reduced audio and/or speech signals is already performed under laboratory conditions.

However, if field measurements are to be performed, there is normally no reference signal available, since the signal source, i.e. the sound studio or a transmitting antenna, is physically located far away from a measurement point.

It is obvious that for the quality assessment of audio signals the reference signal on which the test signal is based must be known. Since the quality assessment does not require that the test signal be compared continuously with the reference signal, it is possible, assuming that the coding or decoding and the radio path do not change too strongly with time, to compare just a section of the test signal, which is based on a reference signal, with the reference signal. Obviously this section of the test signal which is based on the reference signal and the reference signal itself must be present in the measurement device.

3 Radio programme audio signals which return time after time in the same form are e.g. jingles, which introduce certain radio programmes and remain unchanged over long periods of time since they contribute greatly to the identification of a listener with "his" radio programme. This means that if a jingle is provided once at the transmitter it is possible to perform quality measurements on a received audio and/or speech signal at many differnt places and at many different times.

Methods for recognizing jingles are also already known.

However, these methods serve only to recognize a particular piece of music, e.g for questionnaire purposes or for supervising the correct charging of radiotransmitters, where the same serve merely to recognize whether a particular piece of music has been played or not. These known methods for jingle recognition supply a measure for the agreement with a particular signal only at the end of the jingle. This outcome is useless for a measurement method for the quality assessment of audio and/or speech signals, however, since {--the measurement period has already been concluded when the ooo jingle has been recognized. Equally, an exact compensation of the delay between the test signal and the reference signal is not possible in the known methods for jingle recognition.

=e It is the object of the present invention to provide an exact triggering of a measurement method for the quality S•assessment of audio and/or speech signals.

.oo..i 3a The invention provides a method for triggering a measurement method for the quality assessment of audio and/or speech signals, including the following steps: providing digital values of a reference signal which forms the basis for at least a part of a test signal the quality of which is to be assessed; storing digital values of the test signal at least temporarily; determining the degree of agreement between a section of the values of the reference signal and the values of the test signal; triggering the measurement method as soon as a specified degree of agreement is exceeded.

S. o o The invention also provides a device for triggering a measurement device which implements a measurement method for the quality assessment of audio an/or speech signals, including: a first storage device for storing digital values of a 25 reference signal which forms the basis for at least a part of a test signal the quality of which is to be assessed; second storage device for storing digital values of the test signal at least temporarily; a device for determining the degree of agreement between a section of the values of the reference signal and the values of the test signal; a triggering device for triggering the measurement method executed in the measurement device as soon as a specified 1 degree of agreement is exceeded.

H:\MCooper\Keep\peci\4948.97.doc 18/10/99 4 The present invention is based on the fact that a jingle before a radio transmission is particularly suitable for incorporation in the quality assessment of the radio signal.

The prerequisite for this is that such a jingle is transmitted during the measurement period. The reference signal, i.e. the jingle prior to coding and transmission, can be recorded at the transmitter before the measurement and then brought to the receiver in one way or another, e.g.

via modem or magnetic tape. A jingle detector according to the present invention continuously compares the received signal with the provided or stored reference signal, only a small section of the reference signal being compared here with the test signal in continuous comparison and at least one other section of the reference signal being compared here with the corresponding section of the test signal once a specified degree of agreement has been reached. As soon as an agreement is recognized, the jingle, i.e. the reference signal, is played in synchronism with the test signal which is based on the jingle, since the start of the jingle has been identified, after which any of the known technical measurement methods for comparing the two signals can be used for the quality assessment of the coding, the decoding, the transmission, etc.

A preferred embodiment of the present invention will be explained in more detail below making reference to the enclosed drawings, in which Fig. 1 shows a system arrangement which can implement the present invention; and Fig. 2 shows a schematic block circuit diagram of the device for triggering a measurement method for the quality assessment of audio and/or speech signals.

Fig. 1 shows a schematic system arrangement which can implement the method and the device of the present 5 invention. An audio source 10, which may be a sound studio or also a magnetic tape recorded by a sound studio, is connected to a transmitter 12, which in turn has a transmitting antenna 14 assigned to it. The transmitter 12 can perform an analog/digital conversion of the audio and/or speech signal coming from the audio source 10. The digital audio and/or speech signal is also coded in the transmitter 12, i.e. it is data-reduced, as is known to persons skilled in the art, and is modulated onto a carrier by means of a suitable modulation method, also known to persons skilled in the art, so that the coded and modulated audio and/or speech signal can be radiated over the transmitting antenna 14. The coded and modulated audio and/or speech signal propagates over a radio path 16, to be received by a receiving antenna 18. To persons skilled in the art it is obvious that the radio path 16 is merely representative, since the same can equally well be realized by means of a cable connection, which can carry e.g. digital radio signals or also digital television signals, i.e. multimedia signals.

The coded and modulated audio and/or speech signal received by the receiving antenna 18 is demodulated and decoded by suitable means, and is also analog-digital converted, in a receiver 20 and is fed over a receiving line 22 to a jingle detector 24, which constitutes the device for triggering a measurement method for the quality assessment of audio and/or speech signals and which is connected over a detector connection 26 to a measurement device 28 (Fig. 2) which can perform one of a plurality of measurement methods, known to persons skilled in the art, for the quality assessment of audio and/or speech signals.

A dashed line from the connection of the audio source 10 and the transmitter 12 to the jingle detector 24 represents a reference signal line 30. The dashed representation of the reference signal line 30 is meant to symbolize that this connection between the audio source 10 and the jingle 6 detector 24 need not be a continuous connection, since, as has already been stated, a reference signal, i.e. the audio signal of a jingle prior to the coding and modulation, need only be presented to the jingle detector 24 once or at certain moments in time. In contrast, the unbroken connections represent data connections which are continuously active, at least during a measurement process for the quality assessment of audio signals.

Fig. 2 shows a detailed representation of the jingle detector 24, which in a preferred embodiment may be a personal computer with suitable software and with a suitable operating system. The jingle detector 24 has a storage device 242 for storing the reference signal and for storing the test signal, which is supplied to a digital signal processor card 244 via a test signal input 22. The test signal can be supplied as required to the measurement device via a first output 26a, while a second output 26b of the digital signal processor card 244 will supply the reference signal to the measurement device 28 as required. A communication line 26c serves for initialization tasks and for measurement communications between the jingle detector 24 and the measurement device 28. The fact that the communication line 26c is dashed shows, analagously to the reference signal line 30 of Fig. 1, that the communication line 26c is not continuously active but will signal simply e.g. the begin or the end of a measurement by the measurement device 28.

In a preferred embodiment of the method of the present invention, the reference signal, which had been transferred from the audio source 10 to the jingle detector 24 in some suitable way, was recorded on the storage device 242, which is a hard disk of a standard personal computer. As additional hardware the standard personal computer also contains the digital signal processor card 244 in the form of a plug-in card, which provides the audio test signal 7 input 22 and also the first output 26a and the second output 26b. It is pointed out here that the three lines 26a to 26c, as can already be seen from the reference numerals assigned to them, are contained in the detector connection 26 of Fig.

1. The test signal input 22 of the signal processor card 244, which may contain several signal processors, is, as can be seen from Fig. 1, suitably connected to the receiver The first output 26a and the second output 26b of the digital signal processor card 244 are connected to corresponding inputs of the measurement device 28 for the test signal and for the reference signal respectively.

According to a preferred embodiment of the method of the present invention, a first section of the values of the reference signal is read from the hard disk 242 into a memory of the digital signal processor card 244 at the start of a measurement cycle. This first section may be about s long. In the digital signal processor card 244, this first section of the values of the reference signal is filtered, undersampled and then compared by means of a cross correlation with a section of the test signal treated in the same way, which has been supplied to the digital signal processor card 244 or the storage device 242 over the receiving line 22. The test signal has also been filtered and undersampled.

For persons skilled in the art it is obvious that in the jingle detector 24 an analog/digital conversion of the test signal can be performed by a suitable section of the digital signal processor card 244 if the receiver 20 delivers analog values. If the receiver 20 delivers digital values of the test signal, however, there is no need for an analog/digital conversion in the jingle detector 24. It is also obvious that the cross correlation between a section of the values of the reference signal and a section of the values of the test signal is performed in a digital way. In a preferred embodiment the algorithm for performing the cross 8 correlation, i.e. the arrangement determining the degree of agreement of a section of the values of the reference signal with the values of the test signal, is implemented by software. Other than in this embodiment, the arrangement determining the degree of agreement of a section of the values of the reference signal with the values of the test signal can also be implemented by hardware using suitable shift registers and logic gates, which will essentially perform an exclusive-OR function.

As has already been stated, the comparison between a section of the values of the reference signal and a section of the values of the test signal to be assessed takes place on a section basis. In a preferred embodiment of the present invention, a section consists of 512 sample values of the test signal, this section also being termed a "frame". If the section of the values of the reference signal is made shorter, the comparison operation will execute more quickly, though the number of faulty detections of agreement between the test signal and the reference signal will increase. If the section of the reference signal values which is used to determine a degree of agreement is chosen to be longer, the time needed for this operation does indeed increase, but on the other hand the probability of a faulty detection of an agreement will decrease.

If the degree of agreement or the degree of correlation exceeds a certain value, the method for triggering a measurement method for the quality assessment of audio signals establishes that the values of the test signal just compared with the section of the values of the reference signal represent the beginning of a jingle which is present as reference signal in its original form. If the specified degree of agreement or the specified degree of correlation is exceeded, a measurement method for the quality assessment of audio signals is triggered. The jingle detector 24 announces the beginning of the measurement to the C -9measurement device 28 over the communication line 26c, whereby the measurement device 28 is activated so as to receive a further section of the values of the reference signal over the first output 26a of the jingle detector 24, the corresponding values of the test signal being communicated to the measurement device over the second output 26b of the jingle detector 24 at essentially the same time. After triggering the measurement method, which is executed by the measurement device 28, further sections of the reference signal are read from the hard disk 242 and are output, i.e. transmitted to the measurement device 28, together with the test signal received over the receiving line 22. The first output 26a and the second output 26b may be four-channel audio interfaces or, for stereo outputs, the left channel and the right channel of the digital audio signal. The left channel can then transmit the test signal, which corresponds to the output 26b, whereas the right channel, i.e. the output 26a, will communicate the reference signal from the hard disk 242.

Through the correlation of the sections of the values of the test signal with a corresponding number of values of the reference signal, the delay between the reference signal and the test signal is automatically removed, since the section of the values of the reference signal is compared with the continuous bit stream of the received test signal. A new section of reference signal values which is transmitted from the jingle detector to the measurement device corresponds to the values of the test signal which is based on the reference signal, since transmission of further sections of the test signal to the measurement device does not commence until the jingle detector assumes that the current section of the test signal values which has just been involved in the correlation evaluation is that section which is based on the section of the reference signal values which is used for determining the correlation.

10 Other than for the jingle detector according to the prior art described above, in an embodiment of the present invention the whole jingle apart from the first section of the values of the reference signal will be available to the measurement device for the purposes of quality assessment.

In the prior art the whole jingle would first have to have been played in order to be able to establish afterwards that the test signal concerned was a jingle.

Since the correlation of the two signals means that the delay between them is known, the principle of the method being such that the delay is smaller than a section length or frame length, this delay can also be compensated for at the same time. The first section of the reference signal used by the jingle detector 24 to determine agreement can also be provided for the measurement method for the quality assessment of audio signals if both signals are output simultaneously by the digital signal processor card.

It is pointed out here that for the embodiment described up to now the reference signal on the hard disk 242 is stored permanently, whereas the test signal for correlation is only stored temporarily. After agreement between the section of the values of the reference signal and values of the test signal has been established, further received values of the test signal are not temporarily stored in the jingle detector 24 but are output directly to the measurement device 28 over the second output 26b. If the first section of the values of the reference signal is also to be used for the measurement, however, this is only possible if both signals are output simultaneously by the digital signal processor card 244. If the digital signal processor card 244 has sufficient main memory, a longer section of the test signal can also be stored and delayed in the memory. When the jingle is recognized, the whole jingle and not just that part of the jingle which is transmitted after recognition can be measured.

11 As has already been observed, this phase constitutes the actual measurement phase, which is performed in the measurement device 28. The only function of the jingle detector 24 in this measurement phase is to communicate further sections of the values of the reference signal in synchronism with received values of the test signal to the measurement device 28. To persons skilled in the art it is obvious that the number of values of a section must be the same in the test phase for the test signal and the reference signal. It is also obvious to persons skilled in the art that the reference signal can consist of any number of sections, just as the user wishes. The reference signal must, however, be split into at least two sections, one section then being used by the jingle detector 24 to establish agreement between a corresponding section of the test signal and the first section of the reference signal.

The other section is then used by the measurement device 28 together with a corresponding section of the test signal for the quality assessment of the test signal. As has been described above, however, by temporarily storing a longer section of the test signal the first section of the reference signal and the corresponding section of the test signal can be used for the quality assessment by the measurement device 2F.

If, through suitable software in the jingle detector 24, no signal or a very small signal is output before the start of the measurement phase, i.e. the phase of transmitting the test signal and the reference signal over the outputs 26b and 26a, and after this cited phase, the measurement device 28 can, in a way which is known to persons skilled in the art, be so programmed that the beginning and the end of the measurement phase are recognized automatically. The beginning and the end of the measurement phase are communicated over the communication line 26c from the jingle detector 24 to the measurement device 28.

Claims

2. A method according to claim i, o• wherein the triggering of the measurement method is undertaken as soon as a specified degree of agreement ~is exceeded, so as to compare a further section of the values of the reference signal with the values of the test signal in the temporal relative position of the values of the reference signal and of the test signal when the specified degree of agreement occurs. 9o
3. A method according to claim 1 or 2, wherein the part of the test signal the quality of which is to be assessed and on which the reference signal is based is a jingle which repeats itself at regular or irregular intervals in the test signal. 13
4. A method according to any one of the claims 1 to 3, wherein the test signal is a decoded digital radio signal, while the reference signal is a section of the digital radio signal before this has been coded, transmitted and decoded. A method according to any one of the preceding claims, wherein the reference signal and the test signal are undersampled and filtered before storage so as to obtain digital values of the test signal and the reference signal.
6. A method according to any one of the preceding claims, wherein the degree of agreement between a section of the values of the reference signal and the values of the test signal is determined by means of a correlation. ooo°
7. A method according to any one of the preceding claims, wherein, once the specified degree of agreement occurs, more than one further section of the values of the reference signal are compared with corresponding values of the test signal.
8. A method according to claim 7, e* wherein, prior to occurrence of the degree of agreement between the values of the first section and the values of the reference signal and on subsequent first occurrence of a degree of agreement smaller than that specified, a respective signal is generated which indicates a beginning or an end of the measurement method for the quality assessment of audio and/or 14 speech signals.
9. A device for triggering a measurement device which implements a measurement method for the quality assessment of audio and/or speech signals, including: a first storage device for storing digital values of a reference signal which forms the basis for at least a part of a test signal the quality of which is to be assessed; a second storage device for storing digital values of the test signal at least temporarily; a device for determining the degree of agreement between a section of the values of the reference signal and the values of the test signal; a triggering device for triggering the measurement method executed in the measurement device as soon as a specified degree of agreement is exceeded. A device according to claim 9, oeee wherein the first storage device is a hard disk, while the second storage device is a main memory of a digital signal processor card.
11. A device according to claim 9 or wherein the device for determining the degree of agreement and the triggering device are contained in a digital signal processor card with an input for the test signal as well as a first output for the reference signal and a second output for the test signal, where the first and the second outputs are adapted to be connected to a measurement device for 15 assessing the quality of audio signals.
12. A device according to any one of the claims 9 to 11, further including a communication line which is adapted to be connected to the measurement device so as to announce to the same a start or an end of a measurement. Dated this 18th day of October 1999 FRAUNHOFER-GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG E.V. By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 9 o .9 99* 1* 9 99o