Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Patent
1997-08-13
1999-06-29
Hudspeth, David R.
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
704207, G10L 300
Patent
active
059182032
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention refers to a method and a device for determining the tonality of an audio signal.
DESCRIPTION OF THE PRIOR ART
The basis for the hearing-adjusted coding and data reduction of audio signals is that the coding errors arising during coding are spectrally so shaped that they come to lie below the so-called masked hearing threshold and thus remain inaudible. As a result, the determination of the momentary masked hearing threshold during the coding of an audio signal or within a coder comes to play a crucial role.
The estimation of the masked hearing threshold is normally achieved using a hearing model which is designated "perceptual model". On the one hand the audio input signal is applied to this so-called "perceptual model" or hearing model and on the other hand, after a transformation by means of a filter bank or a frequency transformation performed on a block basis, it is applied to a quantizing/coding stage, which is accessed by the output signal of the hearing model or the perceptual model.
In this context the masking ability of a signal depends on whether the signal is a tone-like or tonal signal or is more a noisy or non-tonal signal, since noisy signals have a much stronger masking effect for coding errors than do tonal signal components. Concerning this, reference is made to R. P. Hellmann: "Asymmetry of Masking between Noise and Tone", Perception and Psychophysics, Vol. 11, pp. 241-246, 1972. For this reason, customary psychoacoustic models, such as the models described in the ISO/MPEG standard (cf. ISO/IEC 11172-3, Annex D), already contain mechanisms for detecting tonal signal components. For example, in the "psychoacoustic model 1" described there, a signal component is classified as "tonal" if its level is a certain factor (7 dB) greater than that of the surrounding frequency lines. In the "psychoacoustic model 2" a determination of the tonality is performed on the basis of a prediction of complex FFT indices, which exhibits only small prediction errors for tonal signals in the ideal case. From this the tonality of the signal components is inferred.
These two known methods permit only an unreliable detection of the tonality, however.
SUMMARY OF THE INVENTION
It is therefore a major object of the present invention to provide a method and a device for determining the tonality of an audio signal which exhibit increased reliability in the registration of the tonality of a signal.
According to a first aspect, the present invention provides a method for determining the tonality of an audio signal with the following steps: blockwise frequency transformation of a digital input signal x(n) to create a real positive-value representation X(k) of the input signal, where k designates the index of a frequency line, and determination of the tonality T of the signal components for the frequency line k according to the following equation: ##EQU2## where F.sub.1 is the filter function of a first digital filter with a first, differentiating characteristic, where F.sub.2 is the filter function of a second digital filter with a second, flat or integrating characteristic or with a characteristic which is less strongly differentiating than the first characteristic, and where d.sub.1 and d.sub.2 are integer constants which, depending on the filter parameters, are so chosen that the delays of the filters are compensated for in each case.
According to a second aspect, the present invention provides a method for determining the tonality of an audio signal with the following steps: blockwise frequency transformation of an input signal x(n) to create a real positive-value representation X(k) of the input signal, where k designates the index of a frequency line, and determination of the tonality T of the signal components for the frequency line k according to the following equation: characteristic and where d is an integer constant which is so chosen that the delay of the filter is compensated for.
According to a third aspect, the present invention provides a device for deter
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Brandenburg Karlheinz
Eberlein Ernst
Gerhauser Heinz
Grill Bernhard
Herre Jurgen
Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung
Hudspeth David R.
Lerner Martin
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