EP1048025A1 - Method for instrumental voice quality evaluation - Google Patents

Method for instrumental voice quality evaluation

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Publication number
EP1048025A1
EP1048025A1 EP99942871A EP99942871A EP1048025A1 EP 1048025 A1 EP1048025 A1 EP 1048025A1 EP 99942871 A EP99942871 A EP 99942871A EP 99942871 A EP99942871 A EP 99942871A EP 1048025 A1 EP1048025 A1 EP 1048025A1
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spectral
calculated
speech signal
evaluated
signal
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EP1048025B1 (en
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Jens Berger
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Deutsche Telekom AG
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Deutsche Telekom AG
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
    • G10L25/48—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 specially adapted for particular use
    • G10L25/69—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 specially adapted for particular use for evaluating synthetic or decoded voice signals
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
    • G10L25/48—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 specially adapted for particular use

Definitions

  • the invention relates to a method for instrumental ("objective") speech quality determination, in which characteristic values for determining the speech quality (speech quality) are derived by comparing properties of a speech signal to be evaluated with properties of a reference speech signal (undisturbed signal).
  • Speech quality determinations of speech signals are generally carried out by means of auditory ("subjective") examinations with test subjects.
  • the aim of instrumental ("objective") methods for determining speech quality is to determine from the properties of the speech signal to be assessed, using suitable computing methods, characteristic values which describe the speech quality of the speech signal to be assessed, without having to resort to judgments from test subjects.
  • the calculated parameters and the underlying method for instrumental language quality determination are considered recognized if a high correlation to the results of auditory comparative examinations is achieved.
  • the language quality values obtained by means of auditory examinations thus represent the target values that are to be achieved by instrumental methods.
  • Known methods for instrumental speech quality determination are based on a comparison of a reference speech signal with the speech signal to be evaluated.
  • the reference speech signal and the speech signal to be evaluated are segmented into short time segments.
  • the spectral properties of the two signals are compared in these segments.
  • the spectral intensity map calculated in this way for each period of time under consideration can be understood as a series of numerical values in which the number of individual values corresponds to the number of frequency bands used, the numerical values themselves represent the calculated intensity values and a continuous index of the frequency bands describes the sequence of the numerical values.
  • the limits of the frequency bands used are kept constant on the frequency axis.
  • the calculated intensities of the speech signal to be evaluated and the reference speech signal in each band are compared with one another.
  • the difference between the two values, or the similarity of the two resulting spectral intensity images, is the basis for the calculation of a quality value
  • a disadvantage of the methods known today in such cases is that when comparing the speech signal to be evaluated with a reference speech signal, differences between the two signal sections in the selected display level flow into the quality characteristic to be calculated, which are not or hardly at all - also perceptible in the auditory test - lead to qualitative impairment.
  • Frequency band limitations and spectral deformations of the speech signal to be evaluated e.g. caused by filter properties of the telephone device or the transmission channel
  • the object of the invention is to reduce the influence of spectral limitations and deformations of the speech signal to be evaluated and of shifts in spectral short-term maxima before comparing the spectral properties of a signal to be tested with a reference speech signal and calculating a quality value in instrumental methods.
  • a spectral weighting function is generated in the invention described here, which is based on medium spectral envelopes, e.g. the average spectral power density, based on the speech signal to be evaluated and the reference speech signal. This also enables the method to be used for non-linear and time-variant transmission.
  • the spectral weighting function is calculated from the quotients of the base values of the mean spectral power density of the signal Phi ⁇ (f) to be evaluated and that of the input signal of the transmission system Phi ⁇ (f) in such a way that the weighting function over
  • the evaluation function a (f) can weight the weighting function W ⁇ (f) differently over the effective range, in the simplest case it is constant 1.
  • the spectral weighting function W ⁇ (f) calculated in this way approximates the mean spectral envelopes of the speech signal and the reference speech signal to be evaluated, so that differences between the two spectral envelopes are only incorporated to a reduced extent in the calculated quality value.
  • the spectral weighting function W ⁇ (f) can be applied to the reference speech signal.
  • the average spectral power density of the reference speech signal is approximated to the signal to be evaluated (FIG. 2a).
  • the spectral weighting function can be applied inverted to the signal to be evaluated. This is equalized and, with regard to its average spectral power density, approximated to the reference speech signal (FIG. 2b).
  • Another part of the invention relates to the correction of shifts in short-term spectral maxima caused by the transmission systems.
  • the intensity is integrated in frequency bands for each time period.
  • the result is a series of intensity values for each spectral representation of a signal section, each individual value representing the intensity in a frequency band.
  • the shifts in short-term spectral maxima can lead to deviating calculated intensities in the frequency bands of the reference speech signal and the speech signal to be evaluated.
  • variable band limits for calculating the spectral intensity mapping is not only limited to the signal in which the described spectral weighting function W ⁇ (f) is also used, but can also be applied to the other signal and even to both signals, ( see FIGS. 2a and 2b).
  • a special exemplary embodiment shows an implementation according to FIG. 3, which is referred to as TOSQA (Telecommunication Objective Speech Quality Assessment). This involves advanced preprocessing of the reference speech signal.
  • TOSQA Telecommunication Objective Speech Quality Assessment
  • speech pauses are recognized here by means of a speech pause recognizer and do not go into the quality measure.
  • the reference speech signal and the speech signal to be evaluated are also filtered with a bandpass 300 ... 3400 Hz and the frequency response of a telephone handset is filtered.
  • the spectral power density is integrated in frequency groups, which form the basis for the calculation of the specific loudness.
  • the calculated loudness patterns are supplemented by an error evaluation function.
  • the calculated quality value is formed from the mean value of the co-correlation coefficients of the specific loudnesses for each short time segment under consideration from the number of evaluated speech segments.

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  • Engineering & Computer Science (AREA)
  • Computational Linguistics (AREA)
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  • Audiology, Speech & Language Pathology (AREA)
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Abstract

In a method for determining speech quality using an objective measure, in order to enhance prediction reliability of the evaluated quality parameters, distortions of the mean spectral envelope are extensively corrected with a weighting function W<SUB>T</SUB>(f) before comparing spectral properties. Additionally, the fixed band limits for integration of spectral power density are suppressed and other band limits are searched for instead in a predetermined optimization area in which the resulting spectral intensity representations of the voice signal to be evaluated and the reference voice signal have maximum similarity. The solutions described can supplement known methods and can be incorporated into their structures.

Description

Verfahren zur instrumentellen SprachqualitätsbestimmungProcedures for instrumental language quality determination
Beschreibungdescription
VorbemerkungPreliminary note
Die Erfindung bezieht sich auf ein Verfahren zur instrumentellen ("objektiven") Sprachqualitätsbestimmung, bei dem durch Vergleich von Eigenschaften eines zu bewertenden Sprachsignals mit Eigenschaften eines Referenzsprachsignals (ungestörtes Signal) Kennwerte zur Bestimmung der Sprachqualität (Sprachgüte) abgeleitet werden.The invention relates to a method for instrumental ("objective") speech quality determination, in which characteristic values for determining the speech quality (speech quality) are derived by comparing properties of a speech signal to be evaluated with properties of a reference speech signal (undisturbed signal).
Sprachqualitätsbestimmungen von Sprachsignalen werden in der Regel mittels auditiver ("subjektiver") Untersuchungen mit Versuchspersonen vorgenommen.Speech quality determinations of speech signals are generally carried out by means of auditory ("subjective") examinations with test subjects.
Das Ziel von instrumentellen ("objektiven") Verfahren zur Sprachqualitätsbestimmung ist es, aus Eigenschaften des zu bewertenden Sprachsignals mittels geeigneter Rechenverfahren Kennwerte zu ermitteln, die die Sprachqualität des zu bewertenden Sprachsignals beschreiben, ohne auf Urteile von Versuchspersonen zurückgreifen zu müssen.The aim of instrumental ("objective") methods for determining speech quality is to determine from the properties of the speech signal to be assessed, using suitable computing methods, characteristic values which describe the speech quality of the speech signal to be assessed, without having to resort to judgments from test subjects.
Die berechneten Kennwerte und das zugrunde gelegte Verfahren zur instrumentellen Sprachqualitätsbestimmung gelten als anerkannt, wenn eine hohe Korrelation zu Ergebnissen auditiver Vergleichsuntersuchungen erreicht wird. Die mittels auditiver Untersuchungen gewonnenen Sprachqualitätswerte stellen somit die Zielwerte dar, die durch instrumenteile Verfahren erreicht werden sollen.The calculated parameters and the underlying method for instrumental language quality determination are considered recognized if a high correlation to the results of auditory comparative examinations is achieved. The language quality values obtained by means of auditory examinations thus represent the target values that are to be achieved by instrumental methods.
Stand der TechnikState of the art
Bekannte Verfahren zur instrumentellen Sprachqualitätsbestimmung beruhen auf einem Vergleich eines Referenzsprachsignals mit dem zu bewertenden Sprachsignal. Dabei werden das Referenzsprachsignal und das zu bewertendes Sprachsignal in kurze Zeitabschnitte segmentiert. In diesen Segmenten werden die spektralen Eigenschaften der beiden Signale verglichen.Known methods for instrumental speech quality determination are based on a comparison of a reference speech signal with the speech signal to be evaluated. The reference speech signal and the speech signal to be evaluated are segmented into short time segments. The spectral properties of the two signals are compared in these segments.
Für die Berechnung der spektralen Kurzzeiteigenschaften kommen verschiedene Ansätze und Modelle zur Anwendung. In der Regel erfolgt die Berechnung der Signalintensität in Frequenzbändern, deren Breite mit zunehmender Mittenfrequenz größer wird. Beispiele für solche Frequenzbänder sind die bekannten Terzbänder oder Frequenzgruppen nach Zwicker (veröffentlicht in Zwicker, E.: "Psychoakustik", Berlin: Springer- Verlag, 1982).Various approaches and models are used to calculate the spectral short-term properties. Usually the signal intensity is calculated in Frequency bands whose width increases with increasing center frequency. Examples of such frequency bands are the known third octave bands or frequency groups according to Zwicker (published in Zwicker, E .: "Psychoakustik", Berlin: Springer-Verlag, 1982).
Die derart berechnete spektrale Intensitätsabbildung für jeden betrachteten Zeitabschnitt läßt sich als Reihe von Zahlenwerten auffassen, in der die Anzahl der Einzelwerte der Anzahl der verwendeten Frequenzbänder entspricht, die Zahlenwerte selbst die berechneten Intensitätswerte darstellen und ein fortlaufender Index der Frequenzbänder die Reihenfolge der Zahlenwerte beschreibt.The spectral intensity map calculated in this way for each period of time under consideration can be understood as a series of numerical values in which the number of individual values corresponds to the number of frequency bands used, the numerical values themselves represent the calculated intensity values and a continuous index of the frequency bands describes the sequence of the numerical values.
Bei den derzeit bekannten Verfahren zur instrumentellen Sprachqualitätsbestimmung werden die Grenzen der benutzten Frequenzbänder auf der Frequenzachse konstant gehalten.In the currently known methods for instrumental speech quality determination, the limits of the frequency bands used are kept constant on the frequency axis.
In jedem betrachteten Zeitsegment werden die berechneten Intensitäten von zu bewertenden Sprachsignal und Referenzsprachsignal in jedem Band miteinander verglichen. Die Differenz beider Werte, bzw. die Ähnlichkeit der beiden entstehenden spektralen Intensitätsabbildungen, stellt die Grundlage für die Berechnung eines Qualitätswertes darIn each time segment under consideration, the calculated intensities of the speech signal to be evaluated and the reference speech signal in each band are compared with one another. The difference between the two values, or the similarity of the two resulting spectral intensity images, is the basis for the calculation of a quality value
(Fig- 1).(Fig- 1).
Solche Verfahren wurden insbesondere für die qualitative Bewertung der Sprache in derSuch procedures have been used in particular for the qualitative assessment of language in the
Telefonieanwendung entwickelt. Beispiele hierfür sind die Veröffentlichungen:Telephony application developed. Examples of this are the publications:
" A perceptual speech-quality measure based on a psychacoustic sound representation" (Beerends, J. G.; Stemerdink, J. A., J. Audio Eng. Soc. 42(1994)3, S.115-123)"A perceptual speech-quality measure based on a psychacoustic sound representation" (Beerends, J.G .; Stemerdink, J.A., J. Audio Eng. Soc. 42 (1994) 3, S.115-123)
"Auditory distortion measure for speech coding" (Wang, S; Sekey, A.; Gersho, A.: IEEE Proc. Int. Conf. acoust, Speech and signalprocessing (1991), S.493-496)."Auditory distortion measure for speech coding" (Wang, S; Sekey, A .; Gersho, A .: IEEE Proc. Int. Conf. Acoust, Speech and signalprocessing (1991), S.493-496).
Der derzeit gültige ITU-T Standard P.861 beschreibt ebenfalls ein derartiges Verfahren: "Objective quality measurement of telephone-band speech codecs" (ITU-T Rec. P.861, Genf 1996). Nachteile bekannter instrumenteller Sprachquaiitäts eßverfahrenThe currently valid ITU-T standard P.861 also describes such a method: "Objective quality measurement of telephone-band speech codecs" (ITU-T Rec. P.861, Geneva 1996). Disadvantages of known instrumental speech quality measuring methods
Der Einsatz von bekannten Verfahren zur instrumentellen Sprachqualitätsbestimmung scheitert an der Zuverlässigkeit der berechneten Qualitätswerte für bestimmte zu bewertende Signaleigenschaften. Insbesondere bei Beeinträchtigungen im zu bewertenden Sprachsignal, wie sie z.B. durch Sprachcodierverfahren mit niedrigen Bitraten oder Kombinationen von unterschiedlichen Störungen hervorgerufen werden, liefern derzeit bekannte Verfahren nur unsichere Qualitätswerte.The use of known methods for instrumental speech quality determination fails due to the reliability of the calculated quality values for certain signal properties to be assessed. Especially when there are impairments in the speech signal to be assessed, such as e.g. are currently known methods provide only uncertain quality values by voice coding methods with low bit rates or combinations of different interference.
Nachteilig bei den heute bekannten Verfahren ist in solchen Fällen, daß bei einem Vergleich zwischen dem zu bewertenden Sprachsignal mit einem Referenzsprachsignal Unterschiede zwischen beiden Signalabschnitten in der gewählten Darstellungsebene in den zu berechnenden Qualitätskennwert einfließen, die nicht oder kaum zu einer - auch im auditiven Test wahrnehmbaren - qualitativen Beeinträchtigung führen.A disadvantage of the methods known today in such cases is that when comparing the speech signal to be evaluated with a reference speech signal, differences between the two signal sections in the selected display level flow into the quality characteristic to be calculated, which are not or hardly at all - also perceptible in the auditory test - lead to qualitative impairment.
Im Rahmen der hier betrachteten Sprachübertragung in Telefonanwendungen tragenWear in the context of the voice transmission considered here in telephone applications
Frequenzbandbegrenzungen und spektrale Verformungen des zu bewertenden Sprachsignals (z.B. hervorgerufen durch Filtereigenschaften des Telefongerätes oder des Übertragungskanals) nur begrenzt zu einer empfundenen qualitativen Beeinträchtigung bei.Frequency band limitations and spectral deformations of the speech signal to be evaluated (e.g. caused by filter properties of the telephone device or the transmission channel) only contribute to a perceived qualitative impairment.
Um diese Mängel teilweise zu vermeiden, wird in einem anderen Ansatz versucht, die linearen Verzerrungen (Frequenzgang) durch ein Korrekturfilter bzw. eine Leistungsübertragungsfunktion zu kompensieren (veröffentlicht in: " A new approach to objective quality-measures based on attribute-matching", Halka, U.; Heute, U., Speech communication, 11(1992)1, S.15-30). Die Anwendung dieses Verfahrens ist jedoch bei nichtlinearer und zeitinvarianter Übertragung nachteilig, da die so berechneteIn order to partially avoid these deficiencies, another approach attempts to compensate for the linear distortions (frequency response) by means of a correction filter or a power transmission function (published in: "A new approach to objective quality-measures based on attribute-matching", Halka , U .; Today, U., Speech communication, 11 (1992) 1, p.15-30). However, the use of this method is disadvantageous in the case of nonlinear and time-invariant transmission, since the method calculated in this way
Kompensationsfunktion nicht mehr ausschließlich die spektralen Verformungen des zu bewertenden Signals beschreibt.Compensation function no longer exclusively describes the spectral deformations of the signal to be evaluated.
Verschiebungen spektraler Kurzzeit-Maxima ("Formantverschiebungen") im zu testenden Signal gegenüber dem Referenzsprachsignal, z.B. verursacht durch Codiersysteme mit niedriger Bitrate, führen bei bekannten Verfahren zu großen Unterschieden in den spektralen Intensitätsabbildungen und gehen damit stark in den berechneten Qualitätswert ein. Untersuchungen haben ergeben, daß in einer auditiven Sprachqualitätsuntersuchung diese Verschiebungen spektraler Kurzzeit-Maxima jedoch nur begrenzten Einfluß auf das Qualitätsurteil haben.Shifts in short-term spectral maxima ("formant shifts") in the signal to be tested compared to the reference speech signal, for example caused by coding systems with a low bit rate, lead to large differences in the spectral intensity maps in known methods and are therefore strongly incorporated into the calculated quality value. Research has shown that in an auditory language quality examination however, these shifts in short-term spectral maxima have only a limited influence on the quality judgment.
Aufgabetask
Die Erfindung stellt sich die Aufgabe, den Einfluß von spektralen Begrenzungen und Verformungen des zu bewertenden Sprachsignals sowie von Verschiebungen spektraler Kurzzeit-Maxima vor dem Vergleich der spektralen Eigenschaften eines zu testenden Signals mit einem Referenzsprachsignal und der Berechnung eines Qualitätswertes in instrumentellen Verfahren zu reduzieren.The object of the invention is to reduce the influence of spectral limitations and deformations of the speech signal to be evaluated and of shifts in spectral short-term maxima before comparing the spectral properties of a signal to be tested with a reference speech signal and calculating a quality value in instrumental methods.
Lösungsolution
Im Gegensatz zu bekannten Ansätzen wird in der hier beschriebenen Erfindung eine spektrale Wichtungsfünktion generiert, die auf mittleren spektralen Einhüllenden, z.B. der mittleren spektralen Leistungsdichte, von zu bewertendem Sprachsignal und Referenzsprachsignal beruht. Dies ermöglicht den Einsatz des Verfahrens ebenfalls bei nichtlinearer und zeitvarianter Übertragung.In contrast to known approaches, a spectral weighting function is generated in the invention described here, which is based on medium spectral envelopes, e.g. the average spectral power density, based on the speech signal to be evaluated and the reference speech signal. This also enables the method to be used for non-linear and time-variant transmission.
Die spektrale Wichtungsf nktion wird aus den Quotienten der Stützwerte der mittleren spektralen Leistungsdichte des zu bewertenden Signals Phiγ(f) und der des Eingangssignals des Übertragungssystems Phiχ(f) derart berechnet, daß die Wichtungsfünktion überThe spectral weighting function is calculated from the quotients of the base values of the mean spectral power density of the signal Phiγ (f) to be evaluated and that of the input signal of the transmission system Phiχ (f) in such a way that the weighting function over
Wτ(f) = a(f) (P iγ(f) / Phiχ(f))W τ (f) = a (f) (P iγ (f) / Phiχ (f))
zu beschreiben ist. Die Bewertungsfunktion a(f) kann die Wichtungsfünktion Wτ(f) an über den Wirkungsbereich unterschiedlich gewichten, sie ist im einfachsten Falle konstant 1.is to be described. The evaluation function a (f) can weight the weighting function Wτ (f) differently over the effective range, in the simplest case it is constant 1.
Die derart berechnete spektrale Wichtungsfünktion Wτ(f) nähert die mittleren spektralen Einhüllenden von zu bewertenden Sprachsignal und Referenzsprachsignal einander an, so daß Unterschiede der beiden spektralen Einhüllenden nur noch vermindert in den berechneten Qualitätswert einfließen. Die spektrale Wichtungsfünktion Wτ(f) kann zum einen auf das Referenzsprachsignal angewendet werden. Dabei wird das Referenzsprachsignal in seiner mittleren spektralen Leistungsdichte dem zu bewertenden Signal angenähert (Fig. 2a).The spectral weighting function W τ (f) calculated in this way approximates the mean spectral envelopes of the speech signal and the reference speech signal to be evaluated, so that differences between the two spectral envelopes are only incorporated to a reduced extent in the calculated quality value. On the one hand, the spectral weighting function W τ (f) can be applied to the reference speech signal. The average spectral power density of the reference speech signal is approximated to the signal to be evaluated (FIG. 2a).
Zum anderen kann die spektrale Wichtungsfünktion invertiert auf das zu bewertende Signal angewendet werden. Dieses wird dadurch entzerrt und, hinsichtlich seiner mittleren spektralen Leistungsdichte, an das Referenzsprachsignal angenähert (Fig. 2b).On the other hand, the spectral weighting function can be applied inverted to the signal to be evaluated. This is equalized and, with regard to its average spectral power density, approximated to the reference speech signal (FIG. 2b).
Ein weiterer Teil der Erfindung bezieht sich auf die Korrektur von Verschiebungen spektraler Kurzzeit-Maxima, die durch die Übertragungssysteme verursacht werden.Another part of the invention relates to the correction of shifts in short-term spectral maxima caused by the transmission systems.
Die Intensität wird für jeden Zeitabschnitt in Frequenzbändern integriert. Resultat ist eine Reihe von Intensitätswerten für jede spektrale Darstellung eines Signalabschnitts, wobei jeder Einzelwert die Intensität in einem Frequenzband repräsentiert. Die Verschiebungen spektraler Kurzzeit-Maxima können hierbei zu abweichenden berechneten Intensitäten in den Frequenzbändern von Referenzsprachsignal und zu bewertenden Sprachsignal führen.The intensity is integrated in frequency bands for each time period. The result is a series of intensity values for each spectral representation of a signal section, each individual value representing the intensity in a frequency band. The shifts in short-term spectral maxima can lead to deviating calculated intensities in the frequency bands of the reference speech signal and the speech signal to be evaluated.
Diese Abweichungen in den spektralen Intensitätsabbildungen - verursacht Verschiebungen spektraler Kurzzeit-Maxima -können durch eine variable Anordnung der Frequenzbänder auf der Frequenzachse reduziert werden. Im Gegensatz zu den konstanten Bandgrenzen bei bekannten Verfahren werden die Bandgrenzen auf der Frequenzachse verschoben. Die Zahl der Frequenzbänder und deren Index bleibt aber konstant . In einer Optimierungsschleife werden dann diejenigen Bandgrenzen akzeptiert, bei denen die beiden entstehenden spektralen Abbildungen von zu bewertenden Sprachsignal und Referenzsprachsignal maximale Ähnlichkeit aufweisen bzw. deren Abstand minimal ist . Diese Optimierung wird für alle Bänder in allen betrachteten Zeitsegmenten durchgeführt.These deviations in the spectral intensity maps - causing shifts in short-term spectral maxima - can be reduced by a variable arrangement of the frequency bands on the frequency axis. In contrast to the constant band limits in known methods, the band limits are shifted on the frequency axis. The number of frequency bands and their index remains constant. In an optimization loop, those band limits are then accepted at which the two spectral images of the speech signal and the reference speech signal to be evaluated have maximum similarity or whose distance is minimal. This optimization is carried out for all bands in all considered time segments.
Der Einsatz variabler Bandgrenzen zur Berechnung der spektralen Intensitätsabbildung ist nicht nur auf das Signal, in dem auch die beschriebene spektrale Wichtungsfünktion Wχ(f) zum Einsatz kommt, beschränkt, sondern kann auch auf das jeweils andere Signal und sogar auf beide Signale angewendet werden, (vgl. Fig. 2a und 2b). Ausführungsbeispiel:The use of variable band limits for calculating the spectral intensity mapping is not only limited to the signal in which the described spectral weighting function Wχ (f) is also used, but can also be applied to the other signal and even to both signals, ( see FIGS. 2a and 2b). Design example:
Ein spezielles Ausführungsbeispiel zeigt eine Realisierung gemäß Fig. 3, die als TOSQA (Telecommunication Objective Speech Quality Assessment) bezeichnet wird. Hierbei erfolgt eine erweiterte Vorverarbeitung des Referenzsprachsignals.A special exemplary embodiment shows an implementation according to FIG. 3, which is referred to as TOSQA (Telecommunication Objective Speech Quality Assessment). This involves advanced preprocessing of the reference speech signal.
In Spezifikation der allgemeinen Realisierungen nach Fig. 2a und 2b werden hier Sprachpausen mittels eines Sprachpausenerkenners erkannt und gehen nicht in das Qualitätsmaß ein. Ebenfalls erfolgt eine Filterung von Referenzsprachsignal und zu bewertendem Sprachsignal mit einem Bandpaß 300...3400 Hz sowie eine Filterung auf den Frequenzgang eines Telefonhandapparates. Die Integration der spektralen Leistungsdichte erfolgt in Frequenzgruppen, die die Basis für die Berechnung der spezifischen Lautheit darstellen.In the specification of the general implementations according to FIGS. 2a and 2b, speech pauses are recognized here by means of a speech pause recognizer and do not go into the quality measure. The reference speech signal and the speech signal to be evaluated are also filtered with a bandpass 300 ... 3400 Hz and the frequency response of a telephone handset is filtered. The spectral power density is integrated in frequency groups, which form the basis for the calculation of the specific loudness.
Die Integration in Frequenzgruppen erfolgt jedoch nicht in festen Frequenzgruppengrenzen, sondern mit den in dieser Erfindung beschriebenen variablen Frequenzgruppengrenzen. Die berechneten Signalleistungen in den so modifizierten Frequenzgruppen bilden die Basis für die Intensitätsberechnung. Hier wurde auf ein Modell zur Berechnung der spezifischen Lautheit nach Zwicker, einer gehörrichtigen Intensitätsabbildung, zurückgegriffen (veröffentlicht in Zwicker, E.: "Psychoakustik", Berlin: Springer- Verlag, 1982).However, the integration into frequency groups does not take place in fixed frequency group limits, but with the variable frequency group limits described in this invention. The calculated signal powers in the frequency groups modified in this way form the basis for the intensity calculation. Here, a model was used to calculate the specific loudness according to Zwicker, an aurally accurate intensity map (published in Zwicker, E .: "Psychoacoustics", Berlin: Springer-Verlag, 1982).
Die berechneten Lautheitsmuster werden in Ergänzung des allgemeinen Ansatzes noch durch eine Fehlerbewertungsfünktion ergänzt. Der berechnete Qualitätswert wird über einen Mittelwert der Koirelationskoeffizienten der spezifischen Lautheiten für jedes betrachtete kurze Zeitsegment über die Zahl der ausgewerteten Sprachsegmente gebildet. In addition to the general approach, the calculated loudness patterns are supplemented by an error evaluation function. The calculated quality value is formed from the mean value of the co-correlation coefficients of the specific loudnesses for each short time segment under consideration from the number of evaluated speech segments.

Claims

Patentansprüche (6) Claims (6)
1. Verfahren zur instrumentellen Sprachqualitätsbestimmung, bei dem durch Vergleich von spektralen Kurzzeiteigenschaften eines zu bewertenden Sprachsignals mit einem Referenzsprachsignal Kennwerte zur Bestimmung der Sprachqualität berechnet werden, d a d u r c h g e k e n n z e i c h n e t, daß vor dem Vergleich der Eigenschaften der Sprachsignale, Unterschiede in mittleren spektralen Einhüllenden verringert werden, indem aus diesen zuerst eine spektrale1. A method for instrumental speech quality determination, in which, by comparing short-term spectral properties of a speech signal to be evaluated with a reference speech signal, characteristic values for determining the speech quality are calculated, characterized in that differences in mean spectral envelopes are reduced by comparing the properties of the speech signals first a spectral one
Wichtungsfünktion berechnet wird, mit der die spektralen Kurzzeit-eigenschaften der Sprachsignale in allen betrachteten Zeitsegmenten gewichtet werden, so daß dieWeighting function is calculated, with which the spectral short-term properties of the speech signals are weighted in all considered time segments, so that the
Unterschiede in den mittleren spektralen Einhüllenden dadurch nur begrenzt in den zu berechnenden Qualitätskennwert einfließen, und daß" für die Berechnung der Signalintensität die Grenzen der benutzten Frequenzbänder variabel gestaltet werden, so daß für jeden betrachteten Signalabschnitt in jeweils allen ausgewerteten Frequenzbändern die berechneten Intensitäten vonDifferences in the mean spectral envelope therefore flow into the quality parameter to be calculated only to a limited extent, and that " for the calculation of the signal intensity, the limits of the frequency bands used are designed to be variable, so that the calculated intensities of for each signal section in each evaluated frequency band
Referenzsprachsignal und zu bewertendem Signal zueinander möglichst geringeReference speech signal and signal to be evaluated to each other as low as possible
Unterschiede aufweisen.Have differences.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß zuerst die mittleren spektralen Einhüllenden von zu bewertenden Sprachsignal und Referenzsprachsignal in2. The method according to claim 1, characterized in that first the average spectral envelope of the speech signal to be evaluated and the reference speech signal in
Form eines mittleren Leistungsdichtespektrums berechnet werden und aus dem Quotienten beider Spektren eine spektrale Wichtungsfünktion Wτ(f) berechnet wird, mit der die Kurzzeit-Leistungsdichtespektren des Referenzsprachsignals vor der Berechnung eines Qualitätskennwertes gewichtet werden.Form a mean power density spectrum are calculated and a spectral weighting function Wτ (f) is calculated from the quotient of the two spectra, with which the short-term power density spectra of the reference speech signal are weighted before the calculation of a quality parameter.
3. Verfahren nach Anspruch 1 und 2, dadurch gekennzeichnet, daß die zu berechnende Wichtungsfünktion Wτ(f) nur aus Teilbereichen der berechneten mittleren spektralen Einhüllenden von zu bewertenden Sprachsignal und Referenzsprachsignal berechnet wird und damit die Unterschiede in mittleren spektralen Einhüllenden zwischen beiden Signalen nur in spektralen Teilbereichen verringert werden.3. The method according to claim 1 and 2, characterized in that the weighting function Wτ (f) to be calculated is calculated only from subregions of the calculated mean spectral envelope of the speech signal and reference speech signal to be evaluated and thus the differences in mean spectral envelopes between the two signals only in spectral sub-areas can be reduced.
4. Verfahren nach Anspruch 1 bis 3, dadurch gekennzeichnet, daß vor Berechnung der Qualitätskennwerte eine Integration der Signalintensität für jeden ausgewerteten kurzen Zeitabschnitt in Frequenzgruppen erfolgt, wobei die Grenzen der Frequenzgruppen auf der Frequenzachse variabel sind, aber die Breite der Frequenzgruppen auf der Tonheitskala konstant bleibt, und daß aus den Signalintensitäten in den Frequenzgruppen eine Berechnung der spezifischen Lautheit erfolgt, wobei die Grenzen der Frequenzgruppen benutzt werden, bei denen die berechneten4. The method according to claim 1 to 3, characterized in that an integration of the signal intensity for each evaluated before calculating the quality parameters short period of time in frequency groups, the limits of the frequency groups on the frequency axis are variable, but the width of the frequency groups remains constant on the tonality scale, and that the signal intensities in the frequency groups are used to calculate the specific loudness, using the limits of the frequency groups where the calculated
Unterschiede in der spezifischen Lautheit zwischen dem zu bewertenden Signal und dem Referenzsprachsignal im jeweils betrachteten Band und Zeitsegment den geringsten Unterschied aufweisen.Differences in the specific loudness between the signal to be evaluated and the reference speech signal in the band and time segment considered in each case have the smallest difference.
5. Verfahren nach Anspruch 1 bis 4, dadurch gekennzeichnet, daß der Qualitäts-kennwert aus der Ähnlichkeit der spektralen Darstellungen in jedem betrachteten Zeitabschnitt berechnet wird, wobei die Ähnlichkeit einen über alle betrachteten Zeitabschnitte gemittelten Korrelationskoeffizienten zwischen der spektralen Darstellung des zu bewertenden Sprachsignals und der spektralen Darstellung des Referenzsprachsignals im jeweiligen Zeitsegment darstellt.5. The method according to claim 1 to 4, characterized in that the quality characteristic value is calculated from the similarity of the spectral representations in each time segment under consideration, the similarity being a correlation coefficient averaged over all the time segments under consideration between the spectral representation of the speech signal to be assessed and the represents spectral representation of the reference speech signal in the respective time segment.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der Korrelations-koeffizient zwischen der spektralen Darstellung des zu bewertenden Sprachsignals und der spektralen Darstellung des Referenzsprachsignals im jeweiligen Zeitsegment nur von einem Teilbereich der spektralen Darstellung berechnet wird, d.h. für die Berechnung des Qualitätskennwertes nicht alle berechneten Spektralwerte berücksichtigt werden. 6. The method according to claim 5, characterized in that the correlation coefficient between the spectral representation of the speech signal to be evaluated and the spectral representation of the reference speech signal in the respective time segment is calculated only from a sub-area of the spectral representation, i.e. not all calculated spectral values are taken into account for the calculation of the quality parameter.
EP99942871A 1998-08-27 1999-08-14 Method for objective voice quality evaluation Expired - Lifetime EP1048025B1 (en)

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DE19840548 1998-08-27
DE19840548A DE19840548C2 (en) 1998-08-27 1998-08-27 Procedures for instrumental language quality determination
PCT/EP1999/005972 WO2000013173A1 (en) 1998-08-27 1999-08-14 Method for instrumental voice quality evaluation

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