JP2017152067A - Audio device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an audio device capable of reducing a load of processing when audio data high in sampling frequency is reproduced and also capable of reducing a consumption power.SOLUTION: An audio device 1 includes: a FFT analysis unit 14 for analyzing a frequency component of audio data to be inputted; a down sampling setting unit 16 and a down sampling processing unit 32 for performing down sampling processing for this audio data when reduction of the sampling frequency of the audio data is possible in a state that the frequency component to be reproduced is maintained based on an analysis result of the FFT analysis unit 14; and a digital-analogue conversion unit 36, an amplifier 40, and a speaker 42 for converting and outputting the data obtained by the down sampling processing into analogue audio signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an audio device that reproduces audio data corresponding to various sampling frequencies.

  2. Description of the Related Art Conventionally, there has been known an apparatus that determines a DVD or HD-DVD from medium management information and sets a sampling frequency corresponding to the determined medium type when digital-analog conversion is performed on read audio data. (For example, refer to Patent Document 1). In this way, by determining the resolution (sampling frequency) of the audio data recorded on the medium, the audio data recorded in, for example, a high resolution (hereinafter referred to as “high resolution”) format is converted into a high resolution format. It is possible to reproduce at a corresponding sampling frequency.

JP 2007-179624 A

  By the way, even if the audio data actually input to the audio device is in the high resolution format, not all frequency components that can be reproduced in the high resolution format are always included. For example, recently, audio data upsampling can be easily performed by using a personal computer application or the like. Therefore, it is possible to up-sample audio data (sampling frequency 44.1 kHz, quantization bit number 16 bits) recorded on a CD to create high-resolution audio data having a sampling frequency 96 kHz and quantization bit number 24 bits. it can. The reproduction of audio data having such a high resolution format is performed using an algorithm corresponding to the high resolution format. However, an audio signal to be actually reproduced does not include a high frequency component of 22.05 kHz or higher. Regardless, since playback is performed as high-resolution audio data, there is a problem that the processing load is heavy and power consumption is high.

  The present invention was created in view of the above points, and an object of the present invention is to reduce the processing load when reproducing audio data having a high sampling frequency and reduce power consumption. Is to provide.

  In order to solve the above-described problems, an audio device according to the present invention includes a frequency component analyzing unit that analyzes a frequency component of input audio data, and a frequency component to be reproduced based on the analysis result by the frequency component analyzing unit. If the sampling frequency of the audio data can be lowered while maintaining the data, downsampling processing means for downsampling the audio data, and the data obtained by the downsampling processing are converted into an analog audio signal. Output means for converting and outputting.

  Thus, when audio data recorded in a format with a high sampling frequency is actually lacking a reproducible high frequency component, this audio data is reproduced by lowering the sampling frequency, It is possible to reduce the processing load of reproduction and reduce power consumption.

  Further, it is desirable that the above-described frequency component analyzing means analyzes the frequency component for a predetermined section of the audio data. By analyzing the frequency components for some sections, the analysis process can be simplified and the processing time can be shortened.

  Further, the predetermined section described above is preferably a section including an audio signal whose signal level after reproduction is equal to or higher than a predetermined value. Thereby, the analysis accuracy of the frequency component can be improved.

  Further, the above-described downsampling processing means can perform audio data downsampling processing when the frequency twice the upper limit of the frequency component of the audio signal to be reproduced is lower than the sampling frequency of the audio data. desirable. As a result, the downsampling process can be performed only when the effect of reducing the processing load of the reproduction and reducing the power consumption can be obtained while maintaining the sound quality (frequency characteristics).

  Further, when the audio data sampling frequency described above is higher than the sampling frequency of the CD sound source, it is desirable to perform analysis by the frequency component analyzing means. A configuration for reproducing audio data having a sampling frequency of a CD sound source is common, and even if downsampling processing with a sampling frequency lower than this is performed, a great effect of reducing processing load and power consumption cannot be expected. On the other hand, with respect to the sampling frequency higher than the sampling frequency of the CD sound source, the higher the processing frequency, the larger the processing load and the power consumption. In this case, a large effect can be obtained by performing downsampling processing. it can.

It is a figure which shows the structure of the audio apparatus of one Embodiment. It is explanatory drawing in the case of performing a 1st downsampling process. It is explanatory drawing in the case of performing a 2nd downsampling process. It is a flowchart which shows the operation | movement procedure which reads and reproduces | regenerates the reproduction data of a music.

  An audio apparatus according to an embodiment to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of an audio apparatus 1 according to an embodiment. The audio device 1 is mounted on a vehicle, for example. 1, the audio apparatus 1 includes a control unit 10, an SD (Secure Digital) interface unit (SD I / F) 20, an audio processing unit 30, an amplifier 40, a display processing unit 50, and an operation unit 60.

  The control unit 10 controls the entire audio apparatus 1. Details of the control unit 10 will be described later. The SD interface unit 20 is for inputting and outputting signals to and from an SD memory card 22 as an external recording medium, and includes an SD card slot and an SD host controller. The SD memory card 22 stores music information including reproduction data and various attribute information for each of a plurality of music. For example, the attribute information includes music artist, title, composer, recorded album, album artist, release date, playback data format (for example, WAV, MP3, etc.), sampling frequency, quantization bit number, etc. Is included.

  The audio processing unit 30 is for reproducing music using reproduction data (audio data) read from the SD memory card 22 by the control unit 10, and performs an audio signal by performing a decoding process for each data format. Is output. This audio signal is amplified by the amplifier 40 and output from the speaker 42. In practice, audio signals having two or more channels are reproduced and output. In the configuration shown in FIG. 1, one amplifier 40 and one speaker 42 are shown in a simplified manner. .

  The display processing unit 50 is for displaying an operation screen for selecting a music or playlist to be played back and information (attached information) about the music being played back, and these images created by the control unit 10. Is displayed on the display device 52 composed of an LCD or the like.

  The operation unit 60 is for accepting various operations by the user, and includes various switches and operation knobs. Note that the operation unit 60 may be configured by using a touch panel arranged on the screen of the display device 52, or the operation unit 60 may be configured by using a remote control unit or the like.

  Next, details of the control unit 10 and the audio processing unit 30 will be described. As shown in FIG. 1, the control unit 10 includes a reproduction music selection unit 12, an FFT (Fast Fourier Transform) analysis unit 14, a downsampling setting unit 16, and a reproduction processing unit 18.

  The playback music selection unit 12 selects a music to be played back in accordance with a user instruction using the operation unit 60. For example, the user selects an album name including a plurality of songs, selects an artist name corresponding to the plurality of songs, or selects a playlist name that specifies a playlist for which the playback order is specified in advance. For example, it is possible to designate a plurality of songs as playback targets, or to designate one or more songs directly from the song list.

  The FFT analysis unit 14 performs an FFT analysis process on the audio data corresponding to the music selected as the reproduction target by the reproduction music selection unit 12 and analyzes the frequency component. For example, the analysis of the frequency component is performed by extracting a predetermined section necessary for the frequency component analysis from all the sections to be reproduced. In addition, from the predetermined section, a section including an audio signal whose signal level after reproduction is equal to or higher than a predetermined value is extracted.

  The down-sampling setting unit 16 performs the reproduction when the sampling frequency of the reproduction data to be reproduced can be lowered based on the analysis result by the FFT analysis unit 14 while maintaining the frequency component to be reproduced. Perform settings for downsampling processing on data. For example, when the frequency twice the upper limit value of the frequency component of the reproduction data is lower than the sampling frequency of the reproduction data, it is determined that the sampling frequency of the reproduction data can be lowered.

  In this embodiment, for example, when the upper limit value of the frequency component actually included in the high-resolution format music having a sampling frequency of 192 kHz or 96 kHz is 22.05 kHz or less (below the sound quality of the CD sound source), the sampling frequency is set. A downsampling process (first downsampling process) is performed to lower the frequency to 44.1 kHz. Further, when the upper limit value of the frequency component actually included in the high-resolution format music having a sampling frequency of 192 kHz is between 22.05 kHz and 48 kHz, a downsampling process for reducing the sampling frequency to 96 kHz (second downsampling) Process). The downsampling setting unit 16 determines whether or not to perform the downsampling process, and if so, sets whether to perform the first or second downsampling process.

  The playback processing unit 18 creates an operation screen for the user to instruct playback start / playback stop, volume / sound quality, etc. for playback of the music selected by the playback music selection unit 12, and displays the contents of these instructions as audio. This is set for the processing unit 30 and the amplifier 40.

  As shown in FIG. 1, the audio processing unit 30 includes a decoding processing unit 32, a downsampling processing unit 34, and a digital-analog (D / A) conversion processing unit 36. The audio processing unit 30 is configured using, for example, a DSP (digital signal processor).

  The decoding processing unit 32 performs predetermined decoding processing corresponding to the format on the reproduction data of the music selected as the reproduction target by the reproduction music selection unit 12 and instructed to start reproduction by the reproduction processing unit 18. For example, in the case of a compression format such as MP3, a process of converting the compressed data into PCM (pulse code modulation) data which is an uncompressed format is performed.

  The downsampling processing unit 34 performs either the first or second downsampling processing on the audio data output from the decoding processing unit 32 in accordance with an instruction from the downsampling setting unit 16. In addition, this downsampling process is abbreviate | omitted when a downsampling process is not required. Further, both the first and second downsampling processes are performed by the downsampling processing unit 34, but two downsampling processing units are provided for the first downsampling process and the second downsampling process. You may do it.

  The digital-analog conversion processing unit 36 converts the audio data output from the decoding processing unit 32 or the downsampling processing unit 34 into an analog audio signal. The converted audio signal is amplified by the amplifier 40 and output from the speaker 42.

  The FFT analysis unit 14 described above corresponds to the frequency component analysis unit, the downsampling setting unit 16 and the downsampling processing unit 34 correspond to the downsampling processing unit, and the digital-analog conversion processing unit 36, the amplifier 40, and the speaker 42 correspond to the output unit. .

  The audio apparatus 1 of the present embodiment has such a configuration, and the operation thereof will be described next.

  FIG. 2 is an explanatory diagram when the first downsampling process is performed. Even if the sampling frequency of the reproduction data is 192 kHz, the frequency component of the audio signal is not necessarily included up to the Nyquist frequency of 96 kHz. In the example shown in FIG. 2A, a case where the sampling frequency is 192 kHz and a frequency component higher than 22.05 kHz is not actually included is shown.

  Similarly, just because the reproduction data sampling frequency is 96 kHz, the frequency component of the audio signal is not necessarily included up to the Nyquist frequency of 48 kHz. In the example shown in FIG. 2B, a case where the sampling frequency is 96 kHz and a frequency component higher than 22.05 kHz is not actually included is shown.

  In such a case, a first down-sampling process with a sampling frequency of 44.1 kHz is performed on these reproduction data. FIG. 2C shows the frequency component of the audio signal after the first downsampling process. As is apparent from FIGS. 2A to 2C, the frequency components of the audio signal before and after the first downsampling process are the same, and the sampling frequency is lowered to 44.1 kHz while maintaining the sound quality. Is possible.

  FIG. 3 is an explanatory diagram when the second down-sampling process is performed. Even if the sampling frequency of the reproduction data is 192 kHz, the frequency component of the audio signal is not necessarily included up to the Nyquist frequency of 96 kHz. In the example shown in FIG. 3A, a case where the sampling frequency is 192 kHz and a frequency component higher than 48 kHz is not actually included is shown.

  In such a case, a second down-sampling process with a sampling frequency of 96 kHz is performed on these reproduction data. FIG. 3B shows the frequency components of the audio signal after the second downsampling process. As is clear from FIGS. 3A and 3B, the frequency components of the audio signal before and after the second downsampling process are the same, and the sampling frequency can be lowered to 96 kHz while maintaining the sound quality. It becomes.

  FIG. 4 is a flowchart showing an operation procedure for reading and reproducing the reproduction data of the music. The reproduction processing unit 18 determines whether reproduction is instructed by the user (step 100). If reproduction is not instructed, a negative determination is made, and this determination operation is repeated. When playback is instructed, an affirmative determination is made in the determination of step 100, and a series of playback operations is started.

  First, the FFT analysis unit 14 extracts a part (predetermined section) of the reproduction data of the music to be reproduced (step 102) and analyzes the frequency component of the reproduction data (step 104). Further, the downsampling setting unit 16 determines whether or not the downsampling process for lowering the sampling frequency of the audio data to be played back is possible based on the analysis result while maintaining the frequency component to be played back. (Step 106). If yes, an affirmative determination is made, and then the downsampling processing unit 16 sets the first or second downsampling process (step 108).

  Next, the decoding processing unit 32 performs decoding processing corresponding to the format on the reproduction data of the music to be reproduced (step 110), and the downsampling processing unit 34 sets the contents set by the downsampling setting unit 16 The first or second downsampling process is performed according to (step 114). The audio data after the downsampling processing is converted into an analog audio signal by the digital-analog conversion processing unit 36, amplified by the amplifier 40, and output from the speaker 42 (step 116).

  If the sampling frequency of the audio data to be reproduced cannot be lowered and a negative determination is made in step 106, after the decoding processing by the decoding processing unit 32 is performed (step 112), analog Are amplified and output from the speaker 42 (step 116).

  As described above, in the audio apparatus 1 according to the present embodiment, when the high-resolution audio data is recorded in the high sampling frequency format and the high frequency component that can be actually reproduced is missing, the sampling frequency When the audio data is reproduced with lowering, the processing load of reproduction can be reduced and the power consumption can be reduced.

  In addition, by analyzing the frequency components for some predetermined sections instead of the entire audio data to be reproduced, the analysis process can be simplified and the processing time can be shortened. In particular, the analysis accuracy of the frequency component can be improved by setting this predetermined section as a section including an audio signal whose signal level after reproduction is a predetermined value or more.

  Also, if the frequency that is twice the upper limit of the frequency component of the audio signal to be played is lower than the sampling frequency of the audio data, the audio quality is downsampled to maintain the sound quality (frequency characteristics). However, the downsampling process can be performed only when an effect of reducing the processing load of reproduction and reducing power consumption can be obtained.

  Further, when the sampling frequency of the audio data is higher than the sampling frequency (44.1 kHz) of the CD sound source (in the case of 192 kHz or 96 kHz), the FFT analysis processing by the FFT analysis unit 14 is performed. A configuration for reproducing audio data having a sampling frequency of a CD sound source is common, and even if downsampling processing with a sampling frequency lower than this is performed, a great effect of reducing processing load and power consumption cannot be expected. On the other hand, with respect to the sampling frequency higher than the sampling frequency of the CD sound source, the higher the processing frequency, the larger the processing load and the power consumption. In this case, a large effect can be obtained by performing the downsampling processing. it can.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention. For example, in the above-described embodiment, one of the two types of downsampling processing (first and second downsampling processing) is performed, but the high-resolution format has two types (192 kHz, 96 kHz) or more sampling frequencies. 3 may be subjected to three types of down-sampling processing including those sampling frequencies.

  In the above-described embodiment, the downsampling process for converting the sampling frequency of the CD sound source to 44.1 kHz is performed, but the frequency that is twice the upper limit of the frequency component of the audio signal to be reproduced is 44. If it is lower than 1 kHz, a down-sampling process for converting to a sampling frequency lower than 44.1 kHz may be performed.

  In the above-described embodiment, the frequency component of the audio signal to be played back is acquired by the FFT analysis process, but other methods may be used. For example, using a first bandpass filter having a passband of 44.1 to 96 kHz and a second bandpass filter having a passband of 96 to 192 kHz, the presence or absence of each passband component is checked. Also good. When the outputs of the first and second bandpass filters are both 0 (including the case of almost 0) for the decoded data corresponding to a predetermined section of the audio data, the first downsampling process is performed. When only the output of the second bandpass filter is 0 (including the case of almost 0), the second downsampling process is performed.

  Further, the user may be notified of whether or not the downsampling process is performed. For example, when a predetermined logo mark is turned on when a high-resolution format music is played back, the sampling frequency of the audio data to be played back is lowered to 44.1 kHz, which is the same as the CD sound source, by performing the first downsampling process. In some cases, the logo mark display is changed from the lit state to the unlit state, or a specific display is provided to inform the user that the sound quality is not high and the downsampling process has been performed separately from the logo mark. May be.

  In the above-described embodiment, audio data or the like of music recorded on the SD memory card 22 is read and a predetermined reproduction operation including downsampling processing is performed. However, other memory cards such as a USB memory card are used. Read audio data of music recorded on CD, DVD, hard disk device, etc., receive it from a server connected to the Internet, or acquire audio data of music distributed from a broadcasting station, etc. The reproduction operation may be performed.

  As described above, according to the present invention, when audio data recorded in a high sampling frequency format is actually missing a reproducible high frequency component, the sampling frequency is lowered and the audio data is recorded. By reproducing data, it is possible to reduce the processing load of reproduction and reduce power consumption.

DESCRIPTION OF SYMBOLS 1 Audio apparatus 10 Control part 12 Playback music selection part 14 FFT analysis part 16 Downsampling setting part 18 Playback processing part 20 SD interface part (SD I / F)
22 SD memory card 30 Audio processing unit 32 Decoding processing unit 34 Downsampling processing unit 36 Digital-analog conversion processing unit 40 Amplifier 42 Speaker 50 Display processing unit 60 Operation unit 52 Display device

Claims (5)

Frequency component analysis means for analyzing the frequency component of the input audio data;
Based on the analysis result by the frequency component analysis means, downsampling processing is performed on the audio data when it is possible to reduce the sampling frequency of the audio data while maintaining the frequency component to be reproduced. Downsampling processing means;
Output means for converting the data obtained by the downsampling processing into an analog audio signal and outputting the analog audio signal;
An audio device comprising: In claim 1,
The audio device according to claim 1, wherein the frequency component analyzing means analyzes a frequency component for a predetermined section of the audio data. In claim 2,
The audio device according to claim 1, wherein the predetermined section is a section including an audio signal having a signal level after reproduction of a predetermined value or more. In any one of Claims 1-3,
The down-sampling processing means performs the down-sampling processing of the audio data when a frequency twice the upper limit value of the frequency component of the audio signal to be reproduced is lower than the sampling frequency of the audio data. An audio device. In any one of Claims 1-4,
An audio apparatus characterized in that the frequency component analysis means performs analysis when the sampling frequency of the audio data is higher than the sampling frequency of a CD sound source.

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