Device and method for calculating loudspeaker signals for a plurality of loudspeakers while using a delay in the frequency domain

Patent metadata

Field	Value
Publication number	US-9666203-B2
Application number	US-201414329457-A
Country	US
Kind code	B2
Filing date	Jul 11, 2014
Priority date	Jan 13, 2012
Publication date	May 30, 2017
Grant date	May 30, 2017

Abstract

A device for calculating loudspeaker signals using a plurality of audio sources, an audio source including an audio signal, includes a forward transform stage for transforming each audio signal to a spectral domain to obtain a plurality of temporally consecutive short-term spectra, a memory for storing a plurality of temporally consecutive short-term spectra for each audio signal, a memory access controller for accessing a specific short-term spectrum for a combination consisting of a loudspeaker and an audio signal based on a delay value, a filter stage for filtering the specific short-term spectrum by using a filter, so that a filtered short-term spectrum is obtained for each audio signal and loudspeaker combination, a summing stage for summing up the filtered short-term spectra for a loudspeaker to obtain summed-up short-term spectra, and a backtransform stage for backtransforming summed-up short-term spectra for the loudspeakers to a time domain to obtain the loudspeaker signals.

First claim

The invention claimed is:

1. A device for calculating loudspeaker signals for a plurality of loudspeakers while using a plurality of audio sources, an audio source comprising an audio signal, said device comprising:
a forward transform stage configured to transform each audio signal, block-by-block, to a spectral domain so as acquire for each audio signal a plurality of temporally consecutive short-term spectra;
a memory configured to store a plurality of temporally consecutive short-term spectra for each audio signal;
a memory access controller configured to access a specific short-term spectrum among the plurality of temporally consecutive short-term spectra for a combination comprising a loudspeaker and an audio signal on the basis of a delay value;
a filter stage configured to filter the specific short-term spectrum for the combination of the audio signal and the loudspeaker by using a filter provided for the combination of the audio signal and the loudspeaker, so that a filtered short-term spectrum is acquired for each combination of an audio signal and a loudspeaker;
a summing stage configured to sum up the filtered short-term spectra for a loudspeaker so as acquire summed-up short-term spectra for each loudspeaker; and
a backtransform stage configured to backtransform, block-by-block, summed-up short-term spectra for the loudspeakers to a time domain so as acquire the loudspeaker signals,
wherein the forward transform stage is configured to determine the sequence of short-term spectra with a stride value from a sequence of temporal samples, so that a first sample of a first block of temporal samples that are converted to a short-term spectrum is spaced apart from a first sample of a second subsequent block of temporal samples by a number of samples which is equal to the stride value,
wherein a short-term spectrum has a block index associated with it which indicates the number of stride values by which the first sample of the short-term spectrum is temporally spaced apart from a reference value, and
wherein the memory access controller is configured to determine the short-term spectrum on the basis of the delay value and the block index of the specific short-term spectrum such that the block index of the specific short-term spectrum equals an integer result of a division of a time duration which corresponds to the delay value and of a time duration which corresponds to the stride value, or is larger than same by 1.

2. The device as claimed in claim 1 , wherein the filter stage is configured to determine, from an impulse response of a filter provided for the combination of a loudspeaker and an audio signal, a modified impulse response in that a number of zeros is inserted at a temporal beginning of the impulse response, the number of zeros depending on the delay value for the combination of the audio signal and the loudspeaker, and on the block index of the specific short-term spectrum for the combination of the audio signal and the loudspeaker.

3. The device as claimed in claim 2 , wherein the filter stage is configured to insert such a number of zeros that a time duration corresponding to the number of zeros is smaller than or equal to the remainder of an integer division of the time duration which corresponds to the delay value and of the time duration which corresponds to the stride value.

4. The device as claimed in claim 3 , wherein the filter comprises a fractional delay filter configured to implement a delay by a fraction of a time duration between two adjacent discrete impulse response values, said fraction depending on the integer result of the division of the time duration which corresponds to the delay value and of the time duration which corresponds to the stride value, and on the number of zeros inserted into the impulse response.

5. The device as claimed in claim 1 , wherein the filter stage is configured to multiply, spectral value by spectral value, the specific short-term spectrum by a transmission function of the filter.

6. The device as claimed in claim 1 , wherein the memory comprises, for each audio source, a frequency-domain delay line with an optional access to the short-term spectra stored for said audio source, an access operation being performable via a block index for each short-term spectrum.

7. The device as claimed in claim 1 ,
wherein the forward transform stage comprises a number of transform blocks that is equal to the number of audio sources,
wherein the backtransform stage comprises a number of transform blocks that is equal to the number of loudspeaker signals,
wherein a number of frequency-domain delay lines is equal to the number of audio sources, and
wherein the filter stage comprises a number of single filters that is equal to the product of the number of audio sources and the number of loudspeaker signals.

8. The device as claimed in claim 1 ,
wherein the forward transform stage and the backtransform stage are configured in accordance with an overlap-save method,
wherein the forward transform stage is configured to decompose the audio signal into overlapping blocks while using a stride value so as acquire the short-term spectra, and
wherein the backtransform stage is configured to discard, following backtransform of the filtered short-term spectra for a loudspeaker, specific areas in the backtransformed blocks and to piece together any portions that have not been discarded, so as acquire the loudspeaker signal for the loudspeaker.

9. The device as claimed in claim 1 ,
wherein the forward transform stage and the backtransform stage are configured in accordance with an overlap-add method,
wherein the forward transform stage is configured to decompose the audio signal into adjacent blocks, while using a stride value, which are padded with zeros in accordance with the overlap-add method, a transform being performed with the blocks that have been zero-padded in accordance with the overlap-add method,
wherein the backtransform stage is configured to sum up, following the backtransform of the spectra summed up for a loudspeaker, overlapping areas of backtransformed blocks so as acquire the loudspeaker signal for the loudspeaker.

10. The device as claimed in claim 1 ,
wherein the forward transform stage and the backtransform stage are configured to perform a digital Fourier transform algorithm or an inverse digital Fourier transform algorithm.

11. The device as claimed in claim 1 , further comprising:
a wave field synthesis operator configured to produce the delay value for each combination of a loudspeaker and an audio source while using a virtual position of the audio source and the position of the loudspeaker, and to provide same to the memory access controller or to the filter stage.

12. The device as claimed in claim 1 , wherein the audio source comprises a directional characteristic, the filter stage being configured to use different filters for different combinations of loudspeakers and audio signals.

13. The device as claimed in claim 1 ,
wherein the forward transform stage is configured to perform the block-by-block transform while using a stride,
wherein the memory access controller is configured to partition the delay value into a multiple of the stride and a remainder, and to access the memory while using the multiple of the stride, so as to retrieve the specific short-term spectrum.

14. The device as claimed in claim 13 , wherein the filter stage is configured to form the filter while using the remainder.

15. The device as claimed in claim 1 ,
wherein the forward transform stage is configured to use a block-by-block fast Fourier transform, th

Assignees

• Franck Andreas
• Rath Michael
• Sladeczek Christoph
• Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E V

Inventors

• Franck Andreas
• Rath Michael
• Sladeczek Christoph

Classifications

• H04R3/12 Primary

  for distributing signals to two or more loudspeakers {(specially adapted for hearing aids H04R25/407)} · CPC title

• H04R29/001

  for loudspeakers (H04R29/007 takes precedence) · CPC title

• G10L19/26 Primary

  Pre-filtering or post-filtering · CPC title

• H04S2420/13

  Application of wave-field synthesis in stereophonic audio systems · CPC title

• H04S2420/07

  Synergistic effects of band splitting and sub-band processing · CPC title