Digital filtering method and device and sound image localizing device

• US 20030023649A1
• Filed: 09/25/2002
• Published: 01/30/2003
• Est. Priority Date: 10/31/1997
• Status: Active Grant

• Current Assignee: Yamaha Corporation
• Original Assignee: Yamaha Corporation
• Inventors: Kamiya, Ryo, Ando, Tomoaki
• Granted Patent: US 6,643,674 B2
• Time in Patent Office: Days
• US Class Current: 708/303
• CPC Class Codes: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

A series of digital data to be filtered is divided into a plurality of frames, and f samples of the digital data of each of the frames are burst-transmitted via a computer bus. In transferring the digital data of any one of the frames, n samples of the digital data belonging to a next frame is transferred, along with the digital data of the one frame, to thereby transfer a time series of the digital data consisting of (f+n) samples that are more than the f samples contained in the one frame. Also, a set of k filter coefficients to be used for filtering arithmetic operations in the frame is burst-transmitted via the computer bus, where n≧k. Filtering arithmetic processor, such as a DSP, connected to the bus carries out filtering arithmetic processing using the transmitted f+n samples of the digital data and k coefficients, to provide filtered data corresponding to at least the number of samples for a single frame. The filtering arithmetic processing may itself be conducted at high speed asynchronously with a predetermined sampling cycle. Thus, the filtering arithmetic operations are performed intermittently on a frame-by-frame basis. By buffering the filtered data and outputting them with the predetermined sampling cycle, there are provided filtered outputs synchronous with the predetermined sampling cycle. Cross-fade synthesis (interpolation) between filtered data of adjoining frames can smoothly interconnect the filtered data of the frames.

Claims

1. A digital filtering method comprising:

a first step of collectively transferring, via a bus of a computer, a plurality of samples of digital data to be filtered;

a second step of executing filtering processing, based on a predetermined filter function, on the plurality of samples of digital data transferred by said first step, at a processing rate higher than a predetermined sampling rate; and

a third step of buffering the digital data having been subjected to the filtering processing by said second step and then outputting, at the predetermined sampling rate, the digital data buffered thereby.

2. A digital filtering method as recited in claim 1 wherein said first step divides a series of the digital data to be filtered into a plurality of data sections and intermittently transfers digital data blocks each comprising a plurality of samples of the digital data belonging to one of the data sections, and when transferring the digital data belonging to any one of the data sections, said first step transfers, along with the digital data belonging to the one data section, part of the digital data belonging to another of the data sections adjoining the one data section, to thereby transfer a time series of the digital data consisting of a greater number of samples than a total number of samples contained in the one data section, and

wherein said second step executes the filtering processing based on the predetermined filter function using said time series of the digital data consisting of a greater number of samples than a total number of samples contained in the one data section, to thereby provide filtered data corresponding to at least the total number of samples contained in the one data section.

3. A digital filtering method as recited in claim 2 wherein the part of the digital data, belonging to the other data section, to be transferred by said first step, consists of a specific number of samples corresponding at least to a given number of coefficients used in the predetermined filter function.

4. A digital filtering method as recited in claim 3 wherein a predetermined number of interpolating samples of digital data are further included as said part of the digital data belonging to the other data section and said second step provides the filtered data consisting of a sum of the total number of samples contained in the one data section and the predetermined number of interpolating samples,

which further comprises a fourth step of buffering, for a next one of the data sections, a part of the filtered data that corresponds to the predetermined number of interpolating samples, and a fifth step of executing a predetermined interpolating process using the part of the filtered data that is buffered by said fourth step in a preceding one of the data sections and another part of the filtered data that corresponds to the total number of samples contained in a current one of the data sections, and

wherein said third step buffers the digital data that have been subjected to the interpolating process and corresponds to the total number of samples in the one data section and then outputs, at the predetermined sampling rate, the digital data buffered thereby.

5. A digital filtering method as recited in claim 4 wherein said first step also transfers, via the bus, a set of coefficients to be used in the filtering processing for the one data section, and said second step executes the filtering processing using the set of coefficients transferred by said first step, and wherein using a different set of the coefficients for each of the data sections, said second step is capable of executing the filtering processing with a time-varying characteristic.

6. A digital filtering method as recited in claim 2 wherein with respect to a first one of the data sections, said first step transfers a time series of f+n samples of the digital data that corresponds to a sum between f samples contained in the first data section and predetermined n samples in a former part of a second one of the data sections following said first data section, and with respect to the second data section, said first step retransfers the n samples of the digital data in the former part of said second data section already transferred with respect to said first data section and also transfers f samples of the digital data in a following part of said second data section, and

wherein said n samples are equivalent or greater in number than a total number k of coefficients in said set of coefficients to be used in the filtering processing, i.e., n≧

k.

7. A digital filtering method as recited in claim 1 wherein said first step also transfers, via the bus, a set of coefficients to be used in the filtering processing, and said second step executes the filtering processing using the set of coefficients transferred by said first step.

8. A digital filtering method as recited in claim 1 wherein said second step includes a step of buffering the plurality of samples of digital data transferred by said first step and executes the filtering processing based on the predetermined filter function on the plurality of samples of digital data buffered by said step of buffering.

9. A digital filtering method comprising:

a first step of dividing, into a plurality of blocks, digital data to be filtered and intermittently transferring, via a bus of a computer, a plurality of samples of the digital data in individual ones of the blocks;

a second step of executing filtering processing on the plurality of samples of digital data transferred by said first step using a different set of filter coefficients for each of the blocks, the filtering processing being executed intermittently on a block-by-block basis in response to intermittent transfer of the digital data of the individual blocks; and

a third step of buffering the digital data having been subjected to the filtering processing by said second step and then outputting the digital data buffered thereby.

10. A digital filtering method comprising:

a first step of dividing, into a plurality of blocks, digital data to be filtered and intermittently transferring, via a bus of a computer, a plurality of samples of the digital data in individual ones of the blocks, the digital data of adjoining blocks being transferred with part of the samples overlapping between the blocks;

a second step of executing predetermined filtering processing on the plurality of samples of digital data transferred by said first step using a different set of coefficients for each of the blocks, the filtering processing being executed intermittently on a block-by-block basis in response to intermittent transfer of the digital data of the individual blocks;

a third step of executing cross-fade synthesis between the digital data of at least two adjoining blocks having been subjected to the filtering processing by said second step; and

a fourth step of buffering the digital data having been subjected to the cross-fade synthesis by said third step and then outputting the digital data buffered thereby.

11. A digital filter device comprising:

a first section that collectively transfers, via a bus of a computer, a plurality of samples of digital data to be filtered;

a second section that executes filtering processing, based on a predetermined filter function, on the plurality of samples of digital data transferred by said first section, at a rate higher than a predetermined sampling rate; and

a third step of buffering the digital data having been subjected to the filtering processing by said second step and then outputting, at the predetermined sampling rate, the digital data buffered thereby.

12. A machine-readable recording medium containing a group of instructions of a program executed by a processor for carrying out filtering processing, said program comprising:

a first step of collectively transferring, via a bus of a computer, a plurality of samples of digital data to be filtered;

a second step of executing filtering processing, based on a predetermined filter function, on the plurality of samples of digital data transferred by said first step, at a rate higher than a predetermined sampling rate; and

a third step of buffering the digital data having been subjected to the filtering processing and then outputting, at the predetermined sampling frequency, the digital data buffered thereby.

13. A machine-readable recording medium as recited in claim 12 where said first step is executed by a program associated with a general-purpose processor of the computer, and said second step and third step are executed by a program associated with a filtering arithmetic processor connected to the bus.

14. A digital filter device comprising:

a first section that divides, into a plurality of blocks, digital data to be filtered and intermittently transfers, via a bus of a computer, a plurality of samples of the digital data in individual ones of the blocks;

a second section that executes filtering processing on the plurality of samples of digital data transferred by said first section using a different set of filter coefficients for each of the blocks, the filtering processing being executed intermittently on a block-by-block basis in response to intermittent transfer of the digital data of the individual blocks; and

a third section that buffers the digital data having been subjected to the filtering processing by said second step and then outputs the digital data buffered thereby.

15. A digital filter device comprising:

a first section that divides, into a plurality of blocks, digital data to be filtered and intermittently transfers, via a bus of a computer, a plurality of samples of the digital data in individual ones of the blocks, the digital data of adjoining blocks being transferred with part of the samples overlapping between the blocks;

a second section that executes predetermined filtering processing on the plurality of samples of digital data transferred by said first step using a different set of coefficients for each of the blocks, the filtering processing being executed intermittently on a block-by-block basis in response to intermittent transfer of the digital data of the individual blocks;

a third section that executes cross-fade synthesis between the digital data of at least two adjoining blocks having been subjected to the filtering processing by said second step; and

a fourth section that buffers the digital data having been subjected to the cross-fade synthesis by said third step and then outputs the digital data buffered thereby.

16. A machine-readable recording medium containing a group of instructions of a program executed by a processor for carrying out filtering processing, said program comprising:

a first step of dividing, into a plurality of blocks, digital data to be filtered and intermittently transferring, via a bus of a computer, a plurality of samples of the digital data in individual ones of the blocks;

a second step of executing filtering processing on the plurality of samples of digital data transferred by said first step using a different set of filter coefficients for each of the blocks, the filtering processing being executed intermittently on a block-by-block basis in response to intermittent transfer of the digital data of the individual blocks; and

a third step of buffering the digital data having been subjected to the filtering processing by said second step and then outputting the digital data buffered thereby.

17. A machine-readable recording medium containing a group of instructions of a program executed by a processor for carrying out filtering processing, said program comprising:

a first step of dividing, into a plurality of blocks, digital data to be filtered and intermittently transferring, via a bus of a computer, a plurality of samples of the digital data in individual ones of the blocks, the digital data of adjoining blocks being transferred with part of the samples overlapping between the blocks;

a second step of executing predetermined filtering processing on the plurality of samples of digital data transferred by said first step using a different set of coefficients for each of the blocks, the filtering processing being executed intermittently on a block-by-block basis in response to intermittent transfer of the digital data of the individual blocks;

a third step of executing cross-fade synthesis between the digital data of at least two adjoining blocks having been subjected to the filtering processing by said second step; and

a fourth step of buffering the digital data having been subjected to the cross-fade synthesis by said third step and then outputting the digital data buffered thereby.

18. A digital filter device for connection to a bus of a computer comprising:

an interface section that collectively receives, via the bus, a predetermined number of samples of digital data at one or more desired points within a predetermined frame period;

a filtering arithmetic processing section that executes predetermined filtering arithmetic processing on the digital data received by said interface section; and

an output section that buffers filtered data outputted by said filtering arithmetic processing section and then outputs the filtered data buffered thereby.

19. A digital filter device as recited in claim 18 wherein said filtering arithmetic processing section executes the filtering arithmetic processing asynchronously with a predetermined sampling cycle.

20. A digital filter device as recited in claim 18 wherein said filtering arithmetic processing section executes the filtering arithmetic processing at a higher rate than a predetermined sampling rate.

21. A digital filter device as recited in claim 18 wherein said output section outputs the buffered filtered data in synchronism with a predetermined sampling cycle.

22. A digital filter device as recited in claim 18 wherein said interface section receives a predetermined number of samples of the digital data for individual ones of a plurality of channels at different points within the frame period, and said filtering arithmetic processing section executes the filtering arithmetic processing for the individual channels within the frame period.

23. A digital filter device as recited in claim 22 wherein said output section buffers filtered data of the individual channels, from said filtering arithmetic processing section, while adding together the filtered data of the individual channels on a per-sample-point basis.

24. A digital filter device as recited in claim 18 wherein said interface section also receives, via the bus, a set of coefficients to be used in said filtering arithmetic processing section, and said filtering arithmetic processing section executes the filtering arithmetic processing using the set of coefficients received by said interface section.

25. A digital filter device as recited in claim 18 wherein said computer divides the digital data to be filtered into a plurality of frames and intermittently transfers, via the bus, digital data blocks, each comprising a plurality of samples of the digital data belonging to one of the frames, to said interface section, and when transferring the digital data of any one of the frames, said computer transfers, along with the digital data of the one frame, part of the digital data belonging to another of the frames adjoining the one frame, to thereby transfer a time series of the digital data consisting of a greater number of samples than a total number of samples contained in the one frame, and

wherein said filtering arithmetic processing section executes the filtering arithmetic processing using said time series of the digital data consisting of a number of samples greater than a total number of samples contained in the one frame, to thereby provide filtered data corresponding to at least the total number of samples in the one frame.

26. A digital filter device as recited in claim 18 wherein said filtering arithmetic processing section executes the filtering arithmetic processing using a unique set of coefficients for each of the frames, and which further comprises an interpolating section that interpolates between filtered data of at least two adjoining frames outputted by said filtering arithmetic processing section.

27. A machine-readable recording medium containing a group of instructions of a program executed by a processor connected to a bus of a computer for carrying out filtering processing, said computer collectively transferring, via the bus, a predetermined number of samples of digital data at one or more desired points within a predetermined frame period, said program comprising:

a first step of receiving the digital data transferred from said computer via the bus;

a second step of executing predetermined filtering arithmetic processing, for at least one frame period, on the digital data received by said first step, the filtering arithmetic processing being executed intermittently in response to reception, by said first step, of the digital data via the bus; and

a third step of buffering filtered data provided by said second step and then outputting the filtered data buffered thereby.

28. An FIR filtering method for dividing input data into a plurality of frames each comprising f samples and transferring the input data to an FIR filter having k taps for intermittent FIR filtering processing on a frame-by-frame basis, said FIR filtering method comprising:

a first step of, in a given frame period, transferring f+n samples of the input data to said FIR filter, for execution of the FIR filtering processing on the f+n samples; and

a second step of, in a next frame period, transferring n+f samples of the input data in such a manner that the n samples transferred in the next frame period are a duplicate of the n samples contained in a latter part of the f+n samples already transferred in the given frame period, for execution of the FIR filtering processing on the n+f samples, and wherein n≧

k.

29. A sound image localizing device for dividing waveform data into a plurality of frames each comprising f samples and intermittently imparting a sound image localization effect to the waveform data on a frame-by-frame basis, said sound image localizing device comprising:

a first storage section that prestores therein coefficient data corresponding to positional information representative of possible positions of a sound source;

a second storage section that stores therein the waveform data;

an FIR-filtering arithmetic processing section that has k taps and generates filtered output data on the basis of the coefficient data and waveform data;

a bus that is connected to said first storage section, second storage section and FIR-filtering arithmetic processing section and capable of burst transmission; and

a control section that reads out, from said first storage section, a group of k coefficient data corresponding to the positional information of a current one of the frames and reads out, on a frame-by-frame basis, more than f+k samples of the waveform data from said second storage section in such a manner that more than the k samples of the waveform data are duplicated between the current frame and a next one of the frames adjoining the current frame, and that executes control such that the coefficient data and waveform data read out thereby are burst-transmitted via said bus to said FIR-filtering arithmetic processing section.

30. A sound image localizing device as recited in claim 29 wherein said control section executes control such that the read-out coefficient data and waveform data are burst-transmitted at such short intervals that movement of the sound source can not be identified through human auditory sense.

31. A sound image localizing device as recited in claim 29 wherein said positional information represents a position of the sound source at a substantially middle point in the frame.

32. A sound image localizing device for dividing waveform data into a plurality of frames each comprising f samples and intermittently imparting a sound image localization effect to the waveform data on a frame-by-frame basis, said sound image localizing device comprising:

a first storage section that prestores therein coefficient data corresponding to positional information representative of possible positions of a sound source;

a second storage section that stores therein the waveform data;

an FIR-filtering arithmetic processing section that has k taps and generates filtered output data on the basis of the coefficient data and waveform data;

a bus that is connected to said first storage section, second storage section and FIR-filtering arithmetic processing section and capable of burst transmission;

a control section that reads out, from said first storage section, a group of k coefficient data corresponding to the positional information of a current one of the frames and reads out, on a frame-by-frame basis, f+k+j samples of the waveform data from said second storage section, and that executes control such that the coefficient data and waveform data read out thereby are burst-transmitted via said bus to said FIR-filtering arithmetic processing section; and

a cross-fade processing section that executes cross-fade processing on j samples of the filtered output data that are duplicated between f+j samples of the filtered output data generated in one of the frames and another f+j samples of the filtered output data generated in a next one of the frames by said FIR-filtering arithmetic processing section.