Apparatus for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function
View Patent ↗An apparatus for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function comprises a filter bank for separating the audio signal into at least two sub-band signals. The sub-band signals are examined with regard to periodicities by an autocorrelation function, to obtain rhythm raw-information for the at least two sub-band signals. To reduce or eliminate the ambiguities of the autocorrelation function for periodical signals, the rhythm raw-information is postprocessed to obtain post-processed rhythm raw-information for the sub-band signal. The rhythm information of the audio signal is established based on the postprocessed rhythm raw-information. By the sub-band-wise ACF postprocessing, ACF ambiguities are already eliminated where they originate, and rhythm portions are added at double tempi, which an autocorrelation function processing does normally not provide, so that, as a result, a more robust determination of the rhythm information of the audio signal arises.
1. Apparatus for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function, comprising:
means for dividing the audio signal into at least two sub-band signals;
means for examining at least one sub-band signal with regard to a periodicity in the at least one sub-band signal by an autocorrelation function, to obtain rhythm raw-information for the sub-band signal, wherein a delay is associated to a peak of the autocorrelation function;
means for postprocessing the rhythm raw-information for the sub-band signal determined by the autocorrelation function, to obtain postprocessed rhythm raw-information for the sub-band signal, so that in the postprocessed rhythm raw-information an ambiguity in an integer multiple of a delay, to which an autocorrelation function peak is associated, is reduced compared to the rhythm raw-information before post processing, or a signal portion is added at an integer fraction of a delay, the integer fraction being determined by dividing “1” by an integer, to which an autocorrelation function peak is associated; and
means for establishing the rhythm information of the audio signal by using the postprocessed rhythm raw-information of the sub-band signal and by using another sub-band signal of the at least two sub-band signals.
2. Apparatus according to claim 1 , wherein the means for postprocessing comprises:
means for calculating a version of the rhythm raw-information of a sub-band signal spread by an integer factor; and
means for subtracting the version of the rhythm raw-information of the sub-band signal spread by an integer factor larger than one, or a version of the rhythm raw-information of the sub-band signal derived from this version, to obtain the postprocessed rhythm raw-information for the sub-band signal.
3. Apparatus according to claim 2 , wherein means for subtracting is disposed to perform, prior to subtracting, a weighting of the spread version with a factor between zero and one, to generate the derived version.
4. Apparatus according to claim 1 , wherein means for postprocessing comprises:
means for calculating a version of the rhythm raw-information compressed by an integer factor larger than one; and
means for adding the compressed version of the rhythm raw-information of the sub-band signal or a version derived therefrom to the rhythm raw-information of the sub-band signal, to obtain the postprocessed rhythm raw-information for the sub-band signal.
5. Apparatus according to claim 4 , wherein the means for adding is disposed to perform, prior to adding, a weighting of the compressed version of the rhythm raw-information by a factor between zero and one, such that a weighted compressed version of the rhythm raw-information is added to the rhythm raw-information of the sub-band signal to generate the derived version.
6. Apparatus according to claim 1 , further comprising:
means for evaluating a quality of the periodicity of the postprocessed rhythm raw-information, to obtain a significance measure for the sub-band signal,
wherein means for establishing is further disposed to establish the rhythm information of the audio signal by considering the significance measure of the sub-band signal.
7. Method for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function, comprising:
dividing the audio signal into at least two sub-band signals,
examining at least one sub-band signal with regard to a periodicity in the at least one sub-band signal by an autocorrelation function, to obtain rhythm raw-information for the sub-band signal, wherein a delay is associated to a peak of the autocorrelation function;
postprocessing the rhythm raw-information for the sub-band signal determined by the autocorrelation function, to obtain postprocessed rhythm raw-information for the sub-band signal, so that in the postprocessed rhythm raw-information an ambiguity in the integer multiple of a delay, to which an autocorrelation function peak is associated, is reduced compared to the rhythm raw-information before post processing, or a signal portion is added at an integer fraction of a delay, the integer fraction being determined by dividing “1” by an integer, to which an autocorrelation function peak is associated; and
establishing the rhythm information of the audio signal by using the postprocessed rhythm raw-information of the sub-band signal and by using a further sub-band signal of the at least two sub-band signals.
8. Apparatus for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function, comprising:
means for examining the audio signal with regard to a periodicity in the audio signal, to obtain rhythm raw-information for the audio signal, wherein a delay is associated to a peak of the autocorrelation function;
means for postprocessing the rhythm raw-information for the audio signal determined by the autocorrelation function, to obtain postprocessed rhythm raw-information for the audio signal by adding a version of the rhythm raw information upset by an integer factor, so that in the postprocessed rhythm raw-information a signal portion is added at an integer fraction of a delay, the integer fraction being determined by dividing “1” by an integer, to which an autocorrelation function peak is associated; and
means for establishing rhythm information of the audio signal by using the postprocessed rhythm raw-information of the audio signal.
9. Apparatus for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function, comprising:
means for examining the audio signal with regard to a periodicity in the audio signal, to obtain rhythm raw-information for the audio signal, wherein a delay is associated to a peak of the autocorrelation function;
means for postprocessing the rhythm raw-information for the audio signal determined by the autocorrelation function, to obtain postprocessed rhythm raw-information for the audio signal, by subtracting a version of the rhythm raw-information weighted by a factor unequal one and spread by an integer factor larger than one; and
means for establishing the rhythm information of the audio signal by using the postprocessed rhythm raw-information of the audio signal.
10. Method for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function, comprising:
examining the audio signal with regard to a periodicity in the audio signal, to obtain rhythm raw-information for the audio signal, wherein a delay is associated to a peak of the autocorrelation function;
postprocessing the rhythm raw-information for the audio signal by the autocorrelation function, to obtain postprocessed rhythm raw-information for the audio signal by adding a version of the rhythm raw information upset by an integer factor, so that in the postprocessed rhythm raw-information a signal portion is added at an integer fraction of a delay, the integer fraction being determined by dividing “1” by an integer, to which an autocorrelation function peak is associated; and
establishing the rhythm information of the audio signal by using the postprocessed rhythm raw-information of the audio signal.
11. Method for analyzing an audio signal with regard to rhythm information of the audio signal by using an autocorrelation function, comprising:
examining the audio signal with regard to a periodicity in the audio signal, to obtain rhythm raw-information for the audio signal, wherein a delay is associated to a peak of the autocorrelation function;
postprocessing the rhythm raw-information for the audio signal determined by the autocorrelation function, to obtain postprocessed rhythm raw-information for the audio signal, by subtracting a version of the rhythm raw-information weighted with a factor unequal one and spread by an integer factor larger than one; and
establishing the rhythm information of the audio signal by using the postprocessed rhythm raw-information of the audio signal.