Device and method for processing a signal in the frequency domain

Patent metadata

Field	Value
Publication number	US-10187741-B2
Application number	US-201615264756-A
Country	US
Kind code	B2
Filing date	Sep 14, 2016
Priority date	Mar 14, 2014
Publication date	Jan 22, 2019
Grant date	Jan 22, 2019

Abstract

A device for processing a signal includes a processor stage configured to filter the signal present in a frequency-domain representation by a filter with a filter characteristic in order to obtain a filtered signal, to provide the filtered or a signal derived from the filtered signal with a frequency-domain window function, in order to obtain a windowed signed, wherein providing has multiplications of frequency-domain window coefficients of the frequency-domain window function by spectral values of the filtered signal or the signal derived from the filtered signal in order to obtain multiplication results, and summing up the multiplication results. Further, the device has a converter for converting the windowed signal or a signal determined using the windowed signal to a time domain in order to obtain the processed signal.

First claim

The invention claimed is:

1. A device for processing a discrete-time signal, comprising:
a processor stage configured to:
filter the signal which is present in a discrete frequency-domain representation by a filter with a filter characteristic by means of a multiplication by a transfer function in order to acquire a filtered signal, and
provide the filtered signal with a frequency-domain window function in order to acquire a windowed signal, wherein providing comprises multiplications of frequency-domain window coefficients of the frequency-domain window function by spectral values of the filtered signal in order to acquire multiplication results, and summing up the multiplication results; and
a converter for converting the windowed signal or a signal determined using the windowed signal to a time domain in order to acquire the processed signal,
wherein the processor stage is configured to perform providing with a frequency-domain window function using the following equation:
Y[k]=X[k]W[ 0]+Σ l∈C Y (l) [k]

wherein the term Y (l) [k] is computed as follows:
Y (l) [k]=W r [l]X r + [k,l]−W i [l]X i − [k,l]+j ( W r [l]X i + [k,l]+W i [l]X r − [k,l ])

wherein k is a frequency index, l is an integer index, C is a set of indices, wherein an index I is comprised in the set C if I is not 0 and the coefficient of the frequency-domain window function W[l] is not 0, wherein W r [l] is a real part of a coefficient of the frequency-domain window function, W i [l] is an imaginary part coefficient of the frequency-domain window function, wherein X + [k,l] and X − [k,l] are calculated by the following equations:
X + [k,l]=X [(( k+l )) L ]+X [(( k−l )) L ]
X − [k,l]=X [(( k+l )) L ]−X [(( k−l )) L ], and

wherein ((k)) L means K mod L, wherein L is the length of FFT blocks, and X[k] are spectral coefficients of the signal which is present in the frequency domain.

2. The device in accordance with claim 1 , wherein the processor stage is further configured to:
filter the signal which is present in the frequency domain by a further filter with a further filter characteristic in order to acquire a further filtered signal,
provide the further filtered signal with a further frequency-domain window function in order to acquire a further windowed signal, and
combine the windowed signal and the further windowed signal.

3. The device in accordance with claim 1 ,
wherein the processor stage is configured to filter the signal which is present in a frequency-domain representation by a further filter with a further filter characteristic,
to form a combination signal from the filtered signal and the further filtered signal,
to provide the combination signal with the frequency-domain window function in order to acquire a windowed combination signal, and
to combine the windowed combination signal with the filtered signal or the further filtered signal.

4. The device in accordance with claim 1 ,
wherein the time-domain signal is an audio signal and the signal which is present in the frequency domain is an audio signal transformed to the frequency domain.

5. The device in accordance with claim 1 ,
wherein the filter comprises a necessitated filter characteristic at a first point in time, the further filter comprises a necessitated filter characteristic at a second, later point in time, and
wherein the first frequency-domain window function approximates a fade-out function in the time domain and the second frequency-domain window function approximates a fade-in function in the time domain.

6. The device in accordance with claim 1 ,
wherein the frequency-domain window function or the further frequency-domain windowing comprises at most 15 or at most 8 non-zero coefficients.

7. The device in accordance with claim 1 , wherein the processor stage is configured to use a maximum number of non-zero frequency-domain window coefficients,
wherein the frequency-domain window coefficient for a zero frequency value is real, and
wherein frequency-domain window coefficients for even indices relative to an index of the zero frequency value are purely imaginary and frequency-domain window coefficients for odd indices relative to the index of the zero frequency value are purely real.

8. The device in accordance with claim 1 , wherein in case the value of the window function W[l] is purely real, the term Y (l) [k] is calculated pursuant to the following rule:
Y (l) [k]=W r [l]X r + [k,l]+jW r [l]X i + [k,l]
or
wherein in case the value of the window function W[l] is purely imaginary, the term Y (l) [k] is calculated pursuant to the following rule:
Y (l) [k]=−W i [l]X i − [k,l]+jW i [l]X r − [k,l].

9. The device in accordance with claim 1 ,
wherein the filter characteristic or the further filter characteristic are HRTF filters for different positions and the signal which is present in the frequency-domain representation is an audio signal for a source at the different positions.

10. The device in accordance with claim 1 , further comprising:
a converter for converting the signal to a frequency-domain representation which is suitable for being used with an overlap-add, an overlap-save or a partitioned convolution algorithm, and
wherein the converter for converting the windowed signal or a signal determined using the windowed signal to the time domain is configured to operate using the overlap-add algorithm, the overlap-save algorithm or the partitioned convolution algorithm.

11. The device in accordance with claim 1 ,
wherein the time-domain signal describes a first audio source,
wherein a further time-domain signal describes a second audio source,
wherein the filter for the first audio source is implemented with a first characteristic and a further filter for the first audio source is implemented with a second characteristic,
wherein the processor stage is additionally configured to operate using a third filter and a fourth filter for the second audio source, wherein the third filter comprises a third filter characteristic which describes a first characteristic of the second audio source at a first point in time, and wherein the fourth filter comprises a fourth filter characteristic which corresponds to a second characteristic of the second audio source at the second point in time,
wherein the processor stage is further configured to calculate the first windowed signal using the frequency-domain window function in order to determine a second windowed signal using a further frequency-domain window function, to determine a third windowed signal using a third frequency-domain window function, and to determine a fourth windowed signal using a fourth frequency-domain window function, and
to combine the windowed signals in order to acquire a combination signal, and
wherein the converter is configured to convert the combination signal to the time domain.

12. The device in accordance with claim 11 , wherein the first characteristic of the first audio source at the first point in time is a first position, wherein the second characteristic of the first audio source at the second point in time is a second, different position, wherein the first characteristic of the second audio source at the first point in time is a first position, and wherein the second characteristic of the second audio source at the second point in time is a second, different position.

13. The device in accordance with claim 1 ,
wherein the processor stage is configured to use the frequency-domain window function which, in the time domain, is a fade-out

Assignees

• Fraunhofer Ges Forschung

Inventors

• Franck Andreas

Classifications

• H04S2400/01

  Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved · CPC title

• H04S7/30

  Control circuits for electronic adaptation of the sound field · CPC title

• H04S3/004 Primary

  For headphones · CPC title

• H04S7/307 Primary

  Frequency adjustment, e.g. tone control (H04S7/301 takes precedence) · CPC title

• G10L19/022

  Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring · CPC title