JP4868041B2 - Data conversion apparatus and data conversion program - Google Patents

Description

  The present invention relates to a data conversion apparatus and a data conversion program that convert and output the speed of an input audio signal.

  Practical use of playback technology that changes the length of the audio signal without changing the pitch of the audio signal, and applies it to audio effects in karaoke and fast-forward playback / slow playback during playback of CDs, videos, DVDs, etc. Has been. This technique can be broadly divided into those based on operations on the time axis and those based on operations on the frequency axis. As a typical example of the former, an OLA (OverLap and Add) method and a PSOLA (Pitch Synchronous OLA) method, which is a developed form thereof, are known. As a representative example of the latter, a phase vocoder is known.

JP 2005-266571 A Japanese Patent Laid-Open No. 10-124082 JP 2005-208627 A

  The OLA method is described in Patent Document 1, for example. In the OLA method, audio data is divided into frame units, a window function is applied to the frames, and then the frames are sequentially arranged so that parts of the frames overlap each other, and the data values of the overlapping parts are added and output. . By changing the overlapping width, the audio data is expanded / shortened. The OLA method has a simple process and can be realized with a simple configuration. On the other hand, discontinuity may occur at the frame junction including the periphery of the overlapping portion of the frames, and noise may occur.

  The PSOLA system is described in Patent Document 2, for example. In the PSOLA system, the pitch of audio data is extracted and the frame size is set to a size based on the extracted pitch in order to reduce the noise at the frame junction generated in the OLA system. The PSOLA method has a problem that it can be applied only to audio data having an extractable pitch, that is, audio data such as a single musical instrument.

  A technique involving an operation on the frequency axis is described in Patent Document 3, for example. In technologies that involve operations on the frequency axis, such as phase vocoders, the audio data is Fourier transformed, the phase is manipulated on the frequency axis, the inverse Fourier transform is performed, and the data is returned to the data on the time axis again. The voice data has been expanded and shortened. This method can obtain a better conversion result than the operation on the time axis such as OLA and PSOLA. However, there is a problem that the processing becomes very complicated because it involves Fourier transform and complex number calculation.

  An object of the present invention is to provide a data conversion apparatus and a data conversion program that can be realized with a simple configuration using the OLA method, and that solves the deterioration of sound quality caused by discontinuity at a frame junction.

An object of the present invention is to obtain a reproduction speed ratio acquisition means for acquiring a reproduction speed ratio representing a ratio of the reproduction speed of the output data to the speed of input data;
Determining means for determining a size of each of the input frame memory and the output frame memory and an overlap ratio for each of the input data and the output data based on the acquired reproduction speed ratio;
Storage means for storing the input data sequentially supplied at the speed in an input buffer;
Data for the input hop size determined based on the size of the input frame memory and the overlap ratio for the input data is extracted from the input buffer and copied to the tail of the input frame memory , and the output frame Copy means for extracting data for an output hop size determined based on a frame size and an overlap ratio with respect to the output data from the head of the output frame and copying it to the output buffer;
Window function applying means for applying a window function to the data of the input frame memory ;
An adding means for adding the data of the input frame memory subjected to the window function and data after the data corresponding to the output hop size from the top of the data of the output frame memory ;
Shift means for shifting the data of the output frame memory added by the adding means to the left by the data of the output hop size and shifting the data of the input frame memory to the left by the data of the input hop size;
Output means for sequentially outputting the data stored in the output buffer as the output data at the reproduction speed;
Have
The determining means determines different frame sizes and overlap ratios in each of slow playback where the acquired playback speed ratio is smaller than “1” and fast playback where the acquired playback speed ratio is larger than “1”. This is achieved by a data converter characterized by being configured as described above.

In a preferred embodiment, the determining means, the overlap ratio for the input data when the slow reproduction is to be greater than the overlap ratio for the input data when the fast playback, the overlap with respect to the input data Determine the ratio.

In a more preferred embodiment, the determining means sets the overlap ratio for the input data during the slow playback to “3” or “4”, and sets the overlap ratio for the input data during the fast playback to “2”. Is determined.

Further, an object of the present invention is to obtain a reproduction speed ratio obtaining step for obtaining a reproduction speed ratio representing a ratio of the reproduction speed of the output data to the speed of input data,
Based on the acquired reproduction speed ratio, the sizes of the input frame memory and the output frame memory, and the overlap ratio for the input data and the output data are determined, and the acquired reproduction speed ratio is “1”. A determination step for determining different frame sizes and overlap ratios in each of slow playback that is smaller than and fast playback that is larger than “1”;
Storing the input data sequentially supplied at the speed in an input buffer;
Data for the input hop size determined based on the size of the input frame memory and the overlap ratio for the input data is extracted from the input buffer and copied to the tail of the input frame memory, and the output frame A copy step of extracting data for an output hop size determined based on a frame size and an overlap ratio with respect to the output data from the head of the output frame and copying it to an output buffer;
A window function applying step for applying a window function to the data of the input frame memory;
An addition step of adding the data of the input frame memory subjected to the window function and the data after the data corresponding to the output hop size from the top of the data of the output frame memory;
A shift step of shifting the data of the added output frame memory to the left by the data of the output hop size, and shifting the data of the input frame memory to the left by the data of the input hop size;
An output step of sequentially outputting the data stored in the output buffer as the output data at the reproduction speed;
Is achieved by a data conversion program that causes a computer to execute.

  According to the present invention, it is possible to provide a data conversion apparatus and a data conversion program that can be realized with a simple configuration using the OLA method, and that solves sound quality degradation caused by discontinuities at the frame junctions. Become.

FIG. 1 is a diagram showing an outline of a data conversion apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the signal conversion unit and the storage unit used according to the present embodiment. FIG. 3 is a flowchart showing an example of a main flow executed in the data conversion apparatus according to the present embodiment. FIG. 4 is a flowchart illustrating an example of the switch processing according to the present embodiment. FIG. 5 is a diagram showing an outline of frame addition in the OLA system. FIG. 6 is a diagram showing an outline of frame addition at the time of slow reproduction. FIG. 7 is a diagram showing an outline of frame addition at the time of slow reproduction. FIG. 8 is a diagram illustrating an example of an input buffer, an input frame, an output frame, and an output buffer according to the present embodiment. FIG. 9 is a diagram illustrating another example of the input buffer, the input frame, the output frame, and the output buffer according to the present embodiment. FIG. 10 is a flowchart illustrating an example of data conversion processing according to the present embodiment. 11A is a diagram for explaining the data arrangement in the subframe of the input frame in step 1003 when i = 1, FIG. 11B is a diagram for explaining the data arrangement in the subframe, and FIG. It is a figure which shows the example of the input frame obtained by repeating a process. 12A to 12C are diagrams illustrating examples of input frames and output frames generated in steps 1005 to 1008.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing an outline of a data conversion apparatus according to an embodiment of the present invention. As shown in FIG. 1, a data conversion apparatus 10 according to this embodiment includes a CPU 11, an input unit 12, a display unit 13, a RAM 14, a ROM 15, a large-scale storage device 16, an input interface (I / F) 17, and a signal conversion. Section 18 and audio circuit 19.

  The input unit 12 includes keys and switches such as a playback speed setting switch and a numeric keypad. The display unit 13 includes, for example, a liquid crystal display device. The CPU 11 detects the switch operation of the input unit 12, determines the reproduction speed ratio based on the switch operation, starts the conversion process based on the switch operation, calculates the parameter used for the conversion process, transmits the parameter to the signal conversion unit 18, and inputs Various processes such as control of the I / F 17 are executed.

  The ROM 14 performs various processes executed by the CPU 11, for example, detection of a switch operation of the input unit 12, determination of a reproduction speed ratio based on the switch operation, activation of a conversion process based on the switch operation, calculation of parameters used for the conversion process, Processing programs such as transmission of parameters to the signal converter 18 and control of the input I / F 17 are stored. The RAM 15 is a data storage area for an input buffer that stores input data acquired by the input I / F 17, an output buffer that is read by the audio circuit 19, an input frame that temporarily stores data being processed, an output frame, and the like. I will provide a. The RAM 15 stores various parameters used in processing. The large-scale storage device 16 includes a hard disk device and a card-type storage device, and can store data input via the input I / F 17 and data converted by the signal conversion unit 18.

  The input I / F 17 is connected to the microphone 20 and has an input terminal 21. The audio signal input from the microphone 20 is digitally converted at the input I / F 17 in accordance with an instruction from the CPU 11 and stored in the RAM 14 or the large-scale storage device 16 as digital input data. In the present embodiment, an audio signal from an audio device can be input via the input terminal 21, and digital input data can be stored in the RAM 14 or the large-scale storage device 16.

  The signal conversion unit 18 executes time expansion processing or time reduction processing based on input data, and generates output data in which the reproduction speed is converted. The configuration of the signal converter 18 and the processing executed in the signal converter 18 will be described later. The audio circuit 19 includes a D / A converter and an amplifier circuit (both not shown), converts the output data into an analog audio signal, amplifies it, and outputs an acoustic signal from the speaker 32.

  FIG. 2 is a block diagram showing the configuration of the signal conversion unit and the storage unit used according to the present embodiment. As shown in FIG. 2, the signal conversion unit 18 according to the present embodiment includes an input frame data generation unit 26, an interframe calculation unit 30, and an output buffer data generation unit 28. The input frame data generation unit 26 reads the input data stored in the input buffer 25 and stores the read input data at a predetermined position in the input frame 27. Further, the output buffer data generation unit 28 extracts predetermined data from the output frame 29 and stores it in the output buffer 31. The output data stored in the output buffer 31 is converted into an analog audio signal by the audio circuit 19 and output from the speaker 32.

  The inter-frame operation unit 30 performs data operations such as data shift in the input frame 27 and the output frame 29, applies a window function to the input frame 27, and adds the data value of the input frame to the data value of the corresponding output frame 29. For example, various processes relating to frames and inter-frame processes are executed.

FIG. 3 is a flowchart showing an example of a main flow executed in the data conversion apparatus according to the present embodiment. As shown in FIG. 3, when the power is turned on, the main flow starts, and the CPU 11 clears the input buffer 25 in the RAM 14, clears the input frame 27, clears the output frame 29, clears the output buffer 31, and various parameters. Execute initialization processing including clearing (step 301)
When the initialization process is completed, the processes after step 302 are repeatedly executed. In the switch process of step 302, it is determined whether or not a switch constituting the input unit 12 has been operated. If a switch operation has been performed, a process according to the operation is executed. FIG. 4 is a flowchart illustrating an example of the switch processing according to the present embodiment. As shown in FIG. 4, the CPU 11 determines whether the playback speed setting switch among the switches constituting the switch 12 is turned on (step 401). If YES is determined in step 401, the CPU 11 acquires the input playback speed ratio based on the operation of the numeric keypad or the operation of the “+ (plus)” key or the “− (minus)” key ( Step 402).

  The reproduction speed ratio indicates the reproduction speed of the converted output data when the speed of the input data is “1”. A reproduction speed ratio of “2” indicates that the output data is reproduced at twice the speed of the input data. A reproduction speed ratio of “0.5” indicates that data is reproduced at the output at half the speed of the input data. In the data conversion process described later, the “stretch ratio” is equivalent to the reciprocal of the reproduction speed ratio, that is, “1 / reproduction speed ratio”.

  Next, the CPU 11 determines the size of the input buffer 25 and the input frame 27, the overlap ratio, the size of the output frame 29, and the size of the output buffer 31 based on the reproduction speed ratio (step 403). In the present embodiment, input data is converted at a specified reproduction speed ratio within a reproduction speed ratio range of 0.5 to 2, and output data obtained by the conversion is output. In the present embodiment, the OLA method is adopted, and input data is converted and output data is acquired without complicated calculations.

  In the OLA method, input data is first divided into input frames of a predetermined size. Each frame is extracted so as to partially overlap, and the output data has a data value such that each frame partially overlaps. An overlap ratio is used as a parameter indicating the degree of overlap of the frames. The overlap ratio indicates how much the frame is shifted relative to the overall frame size. For example, if the overlap ratio is “4”, it means that the frame is shifted by ¼ of the frame size. The amount of frame shift at this time is referred to as a hop size.

  When the frames are superimposed and added, a window function is applied to the frames, and the data subjected to the window function is added. For example, a Hanning window can be used as the window function. If the hop size related to the input data is equal to the hop size related to the output data, the amplitude increases by the overlapped amount, but the original waveform shape is maintained. In addition, if the hop size related to the output data is larger than the hop size related to the input data, the time extension processing is performed, and as a result, so-called slow playback is performed in which the playback speed is slow. On the other hand, if the hop size related to the output data is smaller than the hop size related to the input data, the time shortening process is executed, and as a result, so-called fast playback is achieved in which the playback speed is increased.

  FIG. 5 is a diagram showing an outline of frame addition in the OLA system, and FIG. 6 is a diagram showing an outline of frame addition in slow reproduction. In FIG. 6, since the hop size related to the output data (shown as “HOPSIZE ′” in FIG. 6) is larger than the hop size related to the input data (shown as “HOPSIZE” in FIG. 6), the size of the output frame is also larger than that of the input frame. growing. Further, at the time of superposition, the frame to be superposed moves in the direction of the arrow according to the hop size “HOPSIZE ′” related to the output data.

  If the frame size and overlap ratio are not set appropriately when frames are superimposed, the sound quality deteriorates in both slow playback and fast playback. For example, as shown in FIG. 7, when the overlap ratio is set to “2” which is the minimum value and the slow reproduction is performed after performing the time extension processing, the level of the data value can be kept constant by frame addition. There is a problem that the amplitude does not fluctuate (see the broken line in FIG. 7). In addition, the small overlap ratio has the problem that the discontinuity at the junction point, that is, the discontinuity of the data where the plurality of waveforms are overlapped, cannot be solved by the overlap. It was.

  On the other hand, by increasing the overlap ratio, the discontinuity at the junction point is reduced, but another problem as described below arises. As the overlap ratio is increased, the number of overlapping frames increases. Therefore, the effect of the comb filter is applied in multiple, and as a result, the sound quality is greatly changed. Even when the frame size is increased, the overlapping portion becomes larger, so that the effect of the comb filter is excessively increased.

  The present applicant has found that the overlap ratio is “2” or more in both slow reproduction and fast reproduction by the OLA method, and that the smallest possible value is desirable. In addition, when the overlap ratio is “2”, in the slow reproduction by the time extension process, the problem of the amplitude fluctuation and the problem of discontinuity occur. However, as long as the fast reproduction by the time reduction process, the overlap ratio is It has been found that there is no problem even with the minimum value “2”.

  In the slow reproduction, it is desirable that the overlap ratio is larger than “2” so that the problem of discontinuity does not occur as described above. Further, it has been found that the overlap ratio is preferably “3” or “4” in consideration of the influence of the comb filter effect. In consideration of the ease of processing, in this embodiment, the overlap ratio in slow playback is set to “4”.

  The frame size is preferably determined in consideration of the influence of the comb filter effect. When the overlap ratio is “2”, the applicant of the present invention is about 1/5 of the number of samples corresponding to the sampling frequency, and when the overlap ratio is “4”, 1 / of the number of samples corresponding to the sampling frequency. It was found that about 10 is appropriate. FIG. 8 is a diagram illustrating an example of an input buffer, an input frame, an output frame, and an output buffer according to the present embodiment. The example shown in FIG. 8 shows an example when the playback speed ratio R is slow playback smaller than “1”.

  In this embodiment, the sampling frequency is 44.1 KHz (44,100 Hz), and the sizes (frame sizes) of the input buffer 801 and the input frame 802 are both “4096”. The overlap ratio is “4”, and the size of the subframe corresponding to the value obtained by dividing the frame size by the overlap ratio is “1024” (see reference numeral 811). Although the frame size is strictly different from 1/10 of the sampling frequency, a value closest to “4410”, which is 1/10 of the sampling frequency, among powers of 2 is adopted for the convenience of processing.

  Further, the output frame 803 according to the present embodiment has a subframe 831 having a size (1024 / R) obtained by dividing the size of the subframes of the input buffer 801 and the input frame 802 by the reproduction speed ratio at the head thereof. In addition, after the first subframe 831, four subframes (for example, reference numeral 832) having the same size as the subframes of the input buffer 801 and the input frame 802 are arranged.

  The output buffer 804 according to the present embodiment is composed of four subframes (see, for example, reference numeral 841) whose size is the same as that of the first subframe 831 of the output frame (that is, 1024 / R).

  FIG. 9 is a diagram illustrating another example of the input buffer, the input frame, the output frame, and the output buffer according to the present embodiment. The example shown in FIG. 9 shows an example in the case of fast playback where the playback speed ratio R is larger than “1”. The sizes of the input buffer 901 and the input frame 902 at the time of fast reproduction are originally “8192”. The overlap ratio is “2”, and the size of the subframe is “4096”.

  The size of the head subframe 931 of the output frame 903 is a size (4096 / R) obtained by dividing the sizes of the subframes of the input buffer 901 and the input frame 902 by the reproduction speed ratio. Further, behind the first subframe 931, two subframes (for example, reference numeral 932) of the same size as the subframes of the input buffer 901 and the input frame 902 are arranged. In addition, the output buffer 904 according to the present embodiment is composed of two subframes (for example, see reference numeral 941) whose size is the same as that of the first subframe 931 of the output frame (that is, 4096 / R).

  In the present embodiment, the size of the input buffer and the input frame when the reproduction speed ratio is larger than “1”, the set of overlap ratios, and the input buffer and the input buffer when the reproduction speed ratio is smaller than “1”. The size of the input frame and the set of overlap ratios are stored in the RAM 14. Therefore, in step 402 of the switch process, the playback speed ratio is acquired, and in step 403, the size of the input buffer and the input frame and the set of overlap ratios corresponding to the playback speed ratio are acquired.

  When the playback speed ratio is smaller than “1”, that is, in the case of slow playback, the input buffer, the input frame, the output frame, and the data area for the output buffer having the sizes shown in FIG. (Step 404). For example, if the playback speed ratio is “0.8”, the size of the first subframe (see reference numeral 831) of the output frame 803 and the subframe of the output buffer 804 (see reference numeral 841) is “1280”. The frame size of the buffer 804 is “5120”. On the other hand, when the reproduction speed ratio is larger than “1”, that is, in the case of fast reproduction, the input buffer, the input frame, the output frame, and the data area for the output buffer having the sizes shown in FIG. (Step 404). After step 404, another switch process is executed (step 405).

  After the switch process, the CPU 11 and the input I / F 21 execute a data input process (step 303). In the data input process, the CPU 11 refers to a timer (not shown) to determine whether it is a data input timing. If the input timing has arrived, the CPU 11 determines that the input I / F 17 is input. Is instructed to store the input data in the input data buffer 25. The input I / F 17 sequentially stores the input data in the input data buffer. When all the data temporarily stored in the input I / F 17 is stored in the input data buffer, the data input process ends.

  After the data input process, the signal conversion unit 18 executes the data conversion process according to an instruction from the CPU 11 (step 304). FIG. 10 is a flowchart illustrating an example of data conversion processing according to the present embodiment. As shown in FIG. 10, the signal conversion unit 18 initializes a parameter i for specifying a subframe (step 1001).

  Next, the signal converter 18 determines whether or not the parameter i is larger than the overlap ratio (step 1002). When it is determined No in step 1002, the signal conversion unit 18 (input frame data generation unit 26) copies the i-th subframe of the input buffer to the last subframe of the input frame (step 1003). FIG. 11A is a diagram for explaining the data arrangement in the subframe of the input frame in step 1003 when i = 1 and FIG. 11B is the case when i = 2. When data of In (T), In (T + 1), In (T + 2), and In (T + 3) are stored in the input frame 1100 from the first subframe, they are shown in FIGS. As described above, the data of the first and second subframes are stored in the last subframe of the input frame 1110.

  As will be described later, in step 1007, the subframes of the input frame are shifted. Therefore, by repeating step 1002, subframes In (t-3), In (t-2), In (t-1), and In (t) are stored from the beginning in the input frame.

  Next, the signal converter 18 (output buffer data generator 28) copies the first subframe of the output frame to the i-th subframe of the output buffer (step 1004). As will be described later, since the subframes of the output frame are shifted in step 1008, in step 1004, data corresponding to the subframe of the i-th output buffer is arranged in the first subframe.

  After step 1004, the signal conversion unit 18 (interframe calculation unit 30) performs a Hanning window on the input frame (step 1005). Next, the signal processing unit 18 adds the data value of the input frame subjected to the Hanning window and the corresponding data value after the second subframe of the output frame (step 1006). As shown in FIG. 12A, in step 1005, the input frame 1200 is applied to the Hanning window 1202, and an input frame 1203 in which the data value subjected to the Hanning window is stored is obtained. Also, as shown in FIG. 12B, in step 1006, the k-th subframe (k = 1 to 4) of the input frame 1203 storing the data value subjected to the Hanning window, and the output frame 1204 Corresponding data values are added so that the (k + 1) th subframe overlaps.

  After step 1006, the signal conversion unit 18 (input frame data generation unit 26) shifts the data value of the input frame to the left (first side) by one subframe (step 1007). Thereby, the kth subframe (k = 2 to 4) in step 1006 becomes the (k−1) th subframe after step 1007, respectively. The first subframe in step 1006 is discarded. Further, in the next step 1003, the subframe of the input buffer is copied to the fourth subframe of the input frame. In step 1006, for example, the data value “0” may be stored.

  Further, the signal conversion unit 18 (output data buffer data generation unit 28) shifts the data value of the output frame to the left (first side) by the first subframe of the output frame (step 1008). As shown in FIG. 12C, in the output frame 1205 after the process of step 1008, the second to fourth subframes of the output frame 1204 before the process of step 1008 are sequentially stored from the beginning. Is done. In step 1008, the signal conversion unit 18 stores “0” in a predetermined amount of data value at the end (data value corresponding to the size of the first subframe of the output frame: reference numeral 1206).

  After step 1009, the signal converter 18 increments the parameter i (step 1009) and returns to step 1002.

  By the data conversion process shown in FIG. 10, an output buffer including a plurality of subframes (four subframes in slow reproduction) is generated. In the data stored in the output buffer, the data value of the input frame is overlaid based on the number of subframes (overlap ratio: “4” in slow playback). When the playback speed ratio is “0.8”, the hop size of the output buffer is 1 / 0.8 = 1.2 times the hop size of the input frame, and the playback speed is 0.8 times. The time extension process is realized.

  11 and 12, in the data conversion process, an example of generating the output buffer data by the time expansion process for the slow reproduction has been described. However, by the time reduction process for the fast reproduction. Of course, the same can be achieved except that the overlap ratio, input buffer size, input frame size, output frame size, output buffer size, and the size of each subframe are different. No.

  After the data conversion process (step 304 in FIG. 3), the CPU 11 executes a data output process (step 305). In the data output process, the CPU 11 refers to a timer (not shown) to determine whether it is the data output timing, and when the output timing has arrived, the CPU 11 outputs the output data of the RAM 14. Predetermined data is read from the buffer and output to the audio circuit 19. The audio circuit 19 converts the received data into an analog signal, amplifies it, and outputs it to the speaker 22.

  According to the present embodiment, when the time extension process is to be executed, that is, in the case of slow playback, and when the time reduction process is to be executed, that is, in the case of fast playback, the frame size, hop size, The parameters including the wrap ratio are switched, and the data conversion process is executed using the optimum parameters for each. As a result, it is possible to realize fast reproduction and slow generation while suppressing deterioration in sound quality while ensuring simplicity of processing.

  In the present embodiment, the CPU 11 determines the overlap ratio so that the overlap ratio during slow playback is larger than the overlap ratio during fast playback. This is because a problem of discontinuity at the junction of frames is likely to occur during slow reproduction. By increasing the overlap ratio, it is possible to prevent noise caused by the discontinuity.

  In particular, the CPU 11 determines the overlap ratio during slow playback as “3” or “4”, particularly “4” for ease of processing, and determines the overlap ratio during fast playback as “2”. . The overlap ratio “2” in fast reproduction is the minimum value of the overlap ratio as an integer. However, in the case of fast reproduction, even if the minimum value is applied, the sound quality does not deteriorate so much. In addition, this makes it possible to simplify processing by minimizing the number of overlaps during fast playback.

  Further, the CPU 11 determines the frame sizes of the input buffer and the input frame based on the sampling frequency and the playback speed ratio so that the frame size during the slow playback is smaller than the frame size during the fast playback. . This is also because the sound quality does not deteriorate so much during slow playback even with a larger frame size.

  In particular, the CPU 11 sets the frame size of the input buffer and the input frame to a number corresponding to 1/10 of the sampling frequency of the input data at the time of slow playback, and sampling of the input data at the time of fast playback. A number corresponding to 1/5 of the frequency is determined to be a number belonging to a predetermined range. For example, when the sampling frequency is 44.1 KHz (44100 Hz), the frame size is set to “4096” during slow playback, and the frame size is set to “8192” during fast playback.

  The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

10 Data converter 11 CPU
12 Input unit 13 Display unit 14 RAM
15 ROM
16 Large-scale storage device 17 Input I / F
DESCRIPTION OF SYMBOLS 18 Signal conversion part 19 Audio circuit 25 Input buffer 26 Input frame data generation part 27 Input frame 28 Output buffer data generation part 29 Output frame 30 Inter-frame calculating part 31 Output buffer

Claims (4)

Playback speed ratio acquisition means for acquiring a playback speed ratio representing a ratio of the playback speed of the output data to the speed of input data;
Determining means for determining a size of each of the input frame memory and the output frame memory and an overlap ratio for each of the input data and the output data based on the acquired reproduction speed ratio;
Storage means for storing the input data sequentially supplied at the speed in an input buffer;
Data for the input hop size determined based on the size of the input frame memory and the overlap ratio for the input data is extracted from the input buffer and copied to the tail of the input frame memory , and the output frame Copy means for extracting data for an output hop size determined based on a frame size and an overlap ratio with respect to the output data from the head of the output frame and copying it to an output buffer;
Window function applying means for applying a window function to the data of the input frame memory ;
An adding means for adding the data of the input frame memory subjected to the window function and data after the data corresponding to the output hop size from the top of the data of the output frame memory ;
Shift means for shifting the data of the output frame memory added by the adding means to the left by the data of the output hop size and shifting the data of the input frame memory to the left by the data of the input hop size;
Output means for sequentially outputting the data stored in the output buffer as the output data at the reproduction speed;
Have
The determining means determines different frame sizes and overlap ratios in each of slow playback where the acquired playback speed ratio is smaller than “1” and fast playback where the acquired playback speed ratio is larger than “1”. A data conversion device configured as described above. Said determining means that the overlap ratio for the input data when said slow reproduction is the so greater than the overlap ratio for the input data when the fast playback, determines an overlap ratio with respect to the input data The data conversion device according to claim 1, wherein The determining means determines an overlap ratio with respect to the input data at the time of the slow reproduction as “3” or “4”, and an overlap ratio with respect to the input data at the time of the fast reproduction as “2”. The data conversion device according to claim 2. A reproduction speed ratio obtaining step for obtaining a reproduction speed ratio representing a ratio of the reproduction speed of the output data to the speed of the input data;
Based on the acquired reproduction speed ratio, the sizes of the input frame memory and the output frame memory, and the overlap ratio for the input data and the output data are determined, and the acquired reproduction speed ratio is “1”. A determination step for determining different frame sizes and overlap ratios in each of slow playback that is smaller than and fast playback that is larger than “1”;
Storing the input data sequentially supplied at the speed in an input buffer;
Data for the input hop size determined based on the size of the input frame memory and the overlap ratio for the input data is extracted from the input buffer and copied to the tail of the input frame memory, and the output frame A copy step of extracting data for an output hop size determined based on a frame size and an overlap ratio with respect to the output data from the head of the output frame and copying it to an output buffer;
A window function applying step for applying a window function to the data of the input frame memory;
An addition step of adding the data of the input frame memory subjected to the window function and the data after the data corresponding to the output hop size from the top of the data of the output frame memory;
A shift step of shifting the data of the added output frame memory to the left by the data of the output hop size, and shifting the data of the input frame memory to the left by the data of the input hop size;
An output step of sequentially outputting the data stored in the output buffer as the output data at the reproduction speed;
Data conversion program that causes a computer to execute.

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