The resulting filter response is the filter response that is used in filtering in step 130 of FIG. 1.

Different embodiments of the invention provide some variations to the basic method described in FIG. 2. In an embodiment of the invention, the resonance analysis step comprises a step of windowing the sub-band signal data before the step of performing 210 a fast fourier transform in order to reduce spectral artifacts. Windowing, as a man skilled in the art knows, refers to multiplying the data by a predefined window function. In a further embodiment of the invention, the windowing function is weighted towards recent samples. However, the invention is not limited to any specific windowing function, and any windowing function known to a man skilled in the art may be used in different embodiments of the invention.

In various embodiments of the invention different processing steps are taken between the steps of highpass filtering 230 and calculation of a resonance response. As the filtered spectrum resulting from step 230 describes the peaks of the spectrum of the particular sub-band signal, and in step 240 a resonance response is calculated based on the spectrum to specify how to attenuate or otherwise change the signal at those peaks, any further processing of the spectrum between these two steps provides a versatile way to fine-tune the results of the resonance analysis process and the treatment of the audio signal. Various steps to process the spectrum between the steps 230 and 240 are described in the following. In various embodiments of the invention, any one of the following steps A to E may be taken, or more than one, in any order; or none of them.

Step A: Clipping the signal by removing spectrum content that is below a predetermined threshold, leaving only those peaks of the spectrum that are higher than the threshold. By controlling the threshold, one can adjust how high the spectral peaks need to be, before they affect signal processing in the resonance analysis phase.

Step B: Combining spectral information with the corresponding information of previous runs of the resonance analysis step. In an embodiment of the invention, each bin of the spectrum is averaged using a sliding average over a number of runs of the resonance analysis step. Such averaging would allow reacting to peaks that arise slowly, or slow down attenuation of peaks.

Step C: Dynamic remapping of bin values, i.e. by passing the bin value through a mathematical function in order to adjust the bin value. This can be used for example to reduce the spectrum peaks proportionally to their height so that higher peaks are reduced proportionally more than lower peaks. As a result, when the resonance response is calculated in step 240, the higher peaks are then attenuated proportionally less than lower peaks.

Step D: Rounding the peaks of the spectrum by lowpass filtering. This operation widens the peaks of the spectrum. This can reduce the amount of artefacts caused by the processing itself, as a wider spectral feature can be represented by a shorter filter and thus reduce ringing of the resulting filter in the time domain.

Step E: Weighting of certain frequencies. This operation can be used for example for simply weighting certain frequency ranges in the analysis, or for example to provide a better fit of the produced filter response of different sub-bands to each other.

The invention is not limited to the steps A to E in processing of the spectrum between the steps 230 and 240. Embodiments of the invention can process the spectrum using other signal processing steps known to a man skilled in the art.

The invention can be implemented in many different ways. The inventive method can be implemented in a dedicated signal processing device, as a part of a sound processing device such as a digital mixer unit, or for example as computer software stored on a computer readable medium.

FIG. 3 illustrates a sound processing device 300. The device can be for example a digital mixer unit or a dedicated sound processing device.

The device 300 comprises a processor 310 functionally connected to an input 302 and an output 304. The device comprises also a memory element 320 storing instructions 322, 324 to be executed by the processor. The instructions, when executed by the processor 310, cause the processor to perform the inventive method as described in this specification and defined in the claims.

In further embodiments of the invention the device 300 can also comprise other functional elements known to a man skilled in the art such as analog-to-digital (AD) and digital-to-analog (DA) converters. The device can also comprise a plurality of processors. The processors can be dedicated signal processing processors, generic programmable microprocessors or for example processors implemented using FPGAs (field programmable gate arrays).

The invention can also be implemented as a software product, as instructions stored on a storage media such that the instructions, when executed by a processor, cause the processor to perform the inventive method described in the claims. The storage media can be a semiconductor based device such as a volatile memory device, or for example a non-volatile flash memory device. Some further examples of such machine-readable storage media include RAM, ROM, read-only compact discs (CD-ROM), recordable compact discs (CD-R), rewritable compact discs (CD-RW), read-only digital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a variety of recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.), flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.), magnetic and/or solid state hard drives, read-only and recordable Blu-Ray discs, ultra density optical discs, and any other optical or magnetic media. The invention can also be implemented as a downloadable software product that can be installed in a sound processing device.

The invention has several benefits. The invention saves processing power, which reduces the cost of the signal processing chain. The invention allows more processing than prior art solutions while keeping within maximum allowable processing delays in the signal processing chain. The invention allows automatic processing and attenuation of resonances arising in the sound signal during a live event.

Saving of processing power allows processing of more signal channels with the same processor, or executing more signal processing instances on the same processor. Saving of processing power also allows for use of a cheaper processor, and savings in energy use. The inventive method also reduces the need for cache memory due to smaller vector sizes provided by the downsampling operation. The inventive method also provides lower latency, since the process can due to reduced processing power requirements be performed more often i.e. with smaller input block size. The invention also allows processing of low frequencies with smaller FFT sizes, which allows provision of better resolution at low frequencies.

In the following, a number of embodiments of the invention are set out.

According to a first aspect of the invention, a method for processing resonances in a digital sound signal is provided. According to a first embodiment of this first aspect of the invention, the method comprises at least the steps of

- receiving a first block of new sound samples
- filtering said first block into at least two sub-band signals representing different frequency bands of the audio content in said first block, and
- performing at least the following steps S1 to S7 for at least one of said at least two sub-band signals:
- S1) sub-sampling said sub-band signal,
- S2) adding the sub-sampled signal to a first buffer for the corresponding frequency band,
- S3) performing a resonance analysis step for the first buffer for the corresponding frequency band, thereby producing a filter response for the corresponding frequency band,
- S4) convolving the sub-sampled signal or the first complete block of the first buffer with the filter response for the corresponding frequency band,
- S5) adding the convolution result to a second buffer for the corresponding frequency band,
- S6) upsampling the first complete block of said second buffer for the corresponding frequency band, and
- S7) adding the upsampled result to a result buffer for the corresponding frequency band; and
- summing the first complete blocks of said result buffers for each frequency band to form an output block.

According to a second embodiment of this first aspect of the invention,

- at least the following steps are performed for at least one of said at least two sub-band signals:
- adding the sub-band signal to a first buffer for the corresponding frequency band,
- performing a resonance analysis step for the first buffer for the corresponding frequency band, thereby producing a filter response for the corresponding frequency band,
- convolving the sub-band signal or the first complete block of the first buffer with the filter response for the corresponding frequency band, and
- adding the convolution result to a result buffer for the corresponding frequency band.

According to a third embodiment of this first aspect of the invention,

- said step of performing resonance analysis on a buffer comprises at least the steps of
- performing a fast fourier transform on a plurality of latest blocks of said buffer,
- converting the resulting complex response into a real response,
- overpass filtering of said real response to retain only peaks of said real response,
- forming a resonance response based on said filtered real response, and
- forming said filter response based on the resonance response.

According to a fourth embodiment of this first aspect of the invention, the method further comprises at least the step of windowing the data in said buffer before the step of performing (210) a fast fourier transform.

According to a fifth embodiment of this first aspect of the invention, the method further comprises at least the step of clipping said filtered real response after the step of overpass filtering to remove any signal in said filtered real response that is lower than a predetermined threshold.

According to a second aspect of the invention, a sound processing device is provided. The sound processing device has one or more processors and one or more computer-readable storage media. According to a first embodiment of this second aspect of the invention, the storage media has instructions stored thereon that, when executed by the one or more processors, cause the one or more processors to perform at least the steps of

- receiving a first block of new sound samples,
- filtering said first block into at least two sub-band signals representing different frequency bands of the audio content in said first block,
- performing at least the following steps S1 to S7 for at least one of said at least two sub-band signals:
- S1) sub-sampling said sub-band signal,
- S2) adding the sub-sampled signal to a first buffer for the corresponding frequency band,
- S3) performing a resonance analysis step for the first buffer for the corresponding frequency band, thereby producing a filter response for the corresponding frequency band,
- S4) convolving the sub-sampled signal or the first complete block of the first buffer with the filter response for the corresponding frequency band,
- S5) adding the convolution result to a second buffer for the corresponding frequency band,
- S6) upsampling the first complete block of said second buffer for the corresponding frequency band, and
- S7) adding the upsampled result to a result buffer for the corresponding frequency band; and
- summing the first complete blocks of said result buffers for each frequency band to form an output block.

According to a second embodiment of this second aspect of the invention, the storage media further has instructions stored thereon that, when executed by the one or more processors, cause the one or more processors to perform at least the following steps for at least one of said at least two digital signals representing different frequency bands of the signal in said first block:

- adding the signal to a first buffer for the corresponding frequency band,
- performing a resonance analysis step for the first buffer for the corresponding frequency band, thereby producing a filter response for the corresponding frequency band,
- convolving the signal or the first complete block of the first buffer with the filter response for the corresponding frequency band, and
- adding the convolution result to a result buffer for the corresponding frequency band.

According to a third embodiment of this second aspect of the invention, the storage media further has instructions stored thereon that, when executed by the one or more processors, cause the one or more processors to perform in said step of performing resonance analysis on a buffer at least the steps of