JP5051116B2 - Digital audio amplifier - Google Patents

Description

  The present invention relates to a digital audio amplifier that processes a digitized audio signal.

  With the progress of digitalization of audio devices, various effects are applied to analog audio signals, digitalization such as filter processing, and digitalization of analog audio sources are progressing.

  Digitized analog source audio signals vary in level, making optimal settings difficult. In addition, in the case of an analog circuit, if the level of the signal being processed is too large, the gain setting is remotely saturated, so the distortion does not increase so much, but in the case of digital processing, the signal level is the number of quantization bits. If it exceeds the maximum value, the signal waveform will be clipped at the maximum value of the quantization bit number, resulting in a large waveform distortion and unpleasant sound quality. It was. On the other hand, if the signal gain is reduced by taking a margin, there is a problem that the signal / noise level ratio is not increased and the S / N ratio is deteriorated, which is optimal in a digital processing unit such as a DSP. It was required to set the gain.

  An object of the present invention is to provide a digital audio amplifier capable of setting an optimum digital gain corresponding to the level of an input audio signal.

The present invention provides a signal input unit for inputting a digital audio signal, a multiplying unit for multiplying the input digital audio signal by a gain parameter, and a level of the sampling bit number of the digital audio signal output from the multiplying unit. A detecting means for detecting whether or not a clip exceeding the maximum value has occurred, and a clip is generated through the predetermined digital audio signal based on the detection contents of the detecting means when the predetermined digital audio signal is input. Control means for determining the maximum value of the gain parameter not to be fixed and fixing the gain parameter to be supplied to the multiplication means to the determined value.

In the above invention, a signal output unit to which a recording device is connected is further provided, the signal input unit inputs the predetermined digital audio signal twice, and the control means receives the predetermined digital audio signal for the first time. When input, the value of the gain parameter is determined based on the detection content of the detection means, and when the predetermined digital audio signal is input for the second time, the gain parameter supplied to the multiplication means is determined. The signal output unit may output the predetermined digital audio signal, which is input for the second time and multiplied by a gain parameter by the multiplying means, to the recording device .

In the above invention, it further comprises processing means for performing predetermined processing on the digital audio signal output from the multiplication means, and the detection means includes the digital audio signal processed by the processing means and the input digital audio signal. You may make it detect the clip generation | occurrence | production of the signal which added the signal .

In the above invention, the control means reduces the value of the gain parameter supplied to the multiplication means in response to the detection means detecting the clip, and the detection means does not detect the clip continuously for a predetermined time. The normal mode operation for increasing the value of the gain parameter supplied to the multiplication means may be further performed .

  In the present invention, since a predetermined digital audio signal is input and a gain parameter is determined and fixed, when the same predetermined digital audio signal is input again, reproduction / recording can be performed with the best gain.

  Further, in another mode of operation of the control means, it is detected whether or not the level of the signal processed by the processing means has been clipped, and the detection result is reflected in the gain parameter value and fed back to the multiplication means of the input stage. . In this way, by determining whether the level of the processed signal is clipped, it is possible to determine the presence or absence of clipping regardless of the processing content, regardless of what kind of signal processing the processing means performs. By changing the gain parameter dynamically multiplied at the input stage according to the signal, it is possible to quickly cope with signal clipping. Also, if the occurrence of a clip is checked at a short interval (for example, every 2 ms), the clip can be quickly eliminated without causing the user to feel the clip almost.

  Also, when the clip does not occur for a predetermined time, the gain parameter value is increased, so that the digital audio signal can be processed at the optimum level on the spot, and the gain parameter reduced by the occurrence of the clip. If this value is not increased, a fixed gain parameter that is valid for the entire audio source can be determined. If this audio source is replayed using this gain parameter, clipping (distortion) is performed throughout the entire audio source. Playback that does not occur is possible.

  As described above, according to the present invention, a predetermined digital audio signal is input and a gain parameter is determined and fixed. Therefore, when the same predetermined digital audio signal is input again, the SN ratio is good with the best gain. An audio signal can be recorded and reproduced with a sound quality with little distortion. For example, an optimum gain can be set when an analog audio source is digitized and loaded into a storage medium.

  A digital audio amplifier according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a hardware block diagram of a digital audio amplifier according to an embodiment of the present invention. FIG. 2 is a functional block diagram around the DSP 17 of the digital audio amplifier.

  In FIG. 1, the control system of this digital audio amplifier has the same configuration as a computer in which a CPU 10 and each functional unit are connected by a bus. The CPU 10 that controls the operation of the entire apparatus includes a ROM 11, a RAM 12, a flash ROM 13, a display device 14, a panel user interface 15, a remote control receiving unit 16, a DSP 17, a tuner 18, a voice input control unit 19, and a voice output control via a bus. The unit 20 and the UDB interface 21 are connected.

  The ROM 11 stores a basic program for this apparatus. The RAM 12 stores various setting contents that define the operation of the apparatus. The RAM 12 is composed of an SRAM capable of battery backup, and the setting contents are retained even after the power switch is turned off. The flash ROM 13 stores an operation program for this apparatus. Since the flash ROM 13 can be rewritten, the operation program can be upgraded. This version upgrade is performed by another personal computer 3 connected via the USB interface 21. The display device 14 includes an LED matrix display provided on the front panel of the apparatus. The panel user interface 15 includes various button switches on the front panel of the apparatus. The remote control receiver 16 demodulates the infrared code signal sent from the infrared remote controller 2 attached to the apparatus and inputs it to the CPU 10.

The DSP 17 is a processing unit for forming various sound fields by performing filter processing on an input audio signal (digital audio signal). As the sound field to be formed, HALL which forms a sound field of a medium hall level, JAZZ which forms a sound field like a live house, CHURCH which forms a sound field having reverberation like a church, and a sound field for games GAME that forms a sound field, MOVIE that forms a realistic sound field suitable for movies, LIVE that forms a sound field with live feeling, and VDD that forms a three-dimensional virtual sound field.
These sound fields can be selected by the personal computer 3 connected via the USB interface 21.

  4 and 5 are diagrams showing a control screen of a digital audio amplifier control program executed by the personal computer 3. FIG. In FIG. 4A, a button group 40 for selecting a sound field formed by the DSP multiplication and addition processing unit 33, a parameter setting screen 41 for setting parameters of the selected sound field, and an analog for setting the gain of the amplifier 22. Volume 43 and the like are displayed. In FIG. 5B, a sound field selection button group 40 and an equalizer screen 41 'for collating the frequency characteristics of the audio signal are displayed. The sound field is selected by clicking any one of the button group 40, and the selection data is transmitted from the personal computer 3 to the digital audio amplifier 1. Further, by operating the sound field forming (reverberation) parameters and the knobs of each frequency band on the setting screens 41 and 41 ', the change data is transmitted from the personal computer 3 to the digital audio amplifier 1, and the reverberation characteristics and frequency characteristics are transmitted. Will be changed as such. In the digital audio amplifier 1, these data are input from the CPU 10 to the DSP 17.

  When the SETUP 42 button provided at the upper right of the screens of FIGS. 4A and 4B is turned on, a detailed setting screen shown in FIG. 5 is displayed. A slider 44 for controlling the digital volume is displayed therein, and the gain of the digital audio signal in the DSP 17 can be set by operating this slider. However, in the digital gain automatic control function described below in this embodiment, the setting by the user is ignored, and the CPU 10 automatically sets the gain according to the level of the input signal. The set gain is input from the digital audio amplifier 1 (CPU 10) to the personal computer 3, and the personal computer 3 controls the position of the slider 44 in accordance with the input gain.

  In FIG. 1, a tuner 18 receives FM / AM broadcast and inputs the received signal to the audio input control unit 19. As for the reception frequency, the frequency of about 40 broadcasting stations is stored in the battery-backed RAM 12. This frequency can be stored by automatically selecting stations that can be scanned and received, or can be input from the personal computer 3.

  The voice input control unit 19 includes three analog systems (PC IN, AUX1 IN, AUX2 IN) and three digital systems (USB, COAX IN, OPT IN) as input terminals, and any one input terminal is selected by an input selector. Are selected and output to the subsequent stage. The input selector is switched by an input selection signal input from the CPU 10. The CPU 10 inputs an input selection signal to the voice input control unit 19 in accordance with selection inputs from the panel user interface 15 (panel switch), the remote controller 2, the personal computer 3, and the like. When an analog input terminal is selected by the input selector, an audio signal input from the terminal is converted into a digital audio signal by an AD converter and then output to a subsequent stage. When a digital input terminal is selected by the input selector, the digital audio signal input from the terminal is output to the subsequent stage as it is.

  The audio output control unit 20 includes a DA converter and outputs digitally processed audio signals from a plurality of systems. As output terminals, an analog output terminal with a subwoofer terminal, digital USB, OPT OUT, and the like are provided, and an output audio signal can be taken out from each terminal. Further, an analog audio amplifier 22 is connected to the audio output control unit 20, and a speaker terminal which is an output terminal of the audio amplifier 22 is also provided on the back of the apparatus. The gain of the audio amplifier 22, that is, the analog volume can be set by an analog volume encoder (not shown) provided on the front panel and the volume slider 43 at the left end of the control screen in FIG. The speaker 5 is connected to the speaker terminal of the audio amplifier 22. The audio input control unit 19 and the audio output control unit 20 are connected to another audio device 4 such as a DVD player or an MD deck.

  As described above, the personal computer 3 is connected to the USB terminal 21. The personal computer 3 inputs and outputs digital audio signals via the USB terminal 21 and controls the digital audio amplifier by setting software operating on the personal computer 3.

  FIG. 2 is a functional block diagram near the DSP 17. The digital gain automatic control function of this digital audio amplifier will be described with reference to this functional block diagram. The analog audio signal input from the analog input terminal is converted into a digital audio signal by the AD converter 31 and then input to the DSP 17. The AD converter 31 is included in the voice input control unit 19 as described above. The digital audio signal input from the digital input terminal is input directly to the DSP 17.

  In the DSP 17, the input signal (digital audio signal) is input to the coefficient multiplier 32 and multiplied by a coefficient (gain parameter). This coefficient determines the gain of the digital audio signal in the DSP 17 and is a parameter corresponding to a gain in the range of −24 dB to +18 dB. This coefficient is input from the coefficient calculation unit 36. The coefficient calculation unit 36 is realized by a program executed by the CPU 10.

  The digital audio signal multiplied by the coefficient by the coefficient multiplication unit 32 is input to the addition unit 34 and the DSP multiplication / addition processing unit 33. The DSP multiplication / addition processing unit 33 is a processing unit that performs various filter processes, which are so-called DSP processes, forms the various sound fields in the digital audio signal, and equalizes the frequency characteristics. The DSP power addition processing unit 33 outputs the digital audio signal subjected to this processing to the addition unit 34. The adder 34 adds the digital audio signal directly input from the coefficient multiplier 32 and the digital audio signal processed by the DSP power addition processor 33.

  The added digital audio signal is output as an output signal to the audio output control unit 20 and also input to the clip detection unit 35. The clip detection unit 35 determines whether a clip (overflow) has occurred because the level of the digital audio signal exceeds the number of sampling bits (dynamic range in digital processing). The clip detection unit 35 notifies the coefficient calculation unit 36 of the presence or absence of this clip every 2 ms. Based on the presence / absence of clipping, the coefficient calculation unit 36 increases / decreases the coefficient (gain parameter) so that the output of the digital audio signal becomes the maximum level in a range where clipping is not performed. The coefficient obtained in this way is input to the coefficient multiplier 32.

  If the digital audio signal is fixedly processed with the set coefficient (gain parameter) without using the digital gain automatic control function, the functions of the clip detection unit 35 and the coefficient calculation unit 36 may be stopped. .

  FIG. 3 is a flowchart showing the coefficient calculation processing operation in the digital gain automatic control function of the CPU 10. At the start of operation, the coefficient is first initialized to a default value. The default value is, for example, a parameter corresponding to the maximum +18 dB.

  Then, the clip detection result of the clip detector 35 is captured (s2), and it is determined whether the digital audio signal processed by the DSP 17 is clipped, that is, overflowed (s3). In the case of clipping, the coefficient (gain parameter) is lowered by 1 dB and notified to the coefficient multiplier 32 (s4), and the count of the non-clip time counter that continuously counts the time when no clipping occurs is reset. (S5). When the personal computer 3 is displaying the screen of FIG. 5, the gain parameter is transmitted to the personal computer 3 and the display of the slider 44 is changed to the left by one level (s6). After waiting for 2 milliseconds after the above processing (s7), the process returns to s2.

  On the other hand, if it is determined in s3 that no clipping has occurred, the non-clip time counter is incremented (s8). When the count value of the non-clip time counter becomes 5 seconds or more (s9), if the gain is too low, the coefficient is increased by 1 dB and notified to the coefficient multiplier 32 (s10). Proceed to s5.

  As described above, by controlling the coefficient to the maximum value within the range where the audio signal is not clipped in the DSP 17 as the digital processing unit, it is possible to perform the audio signal processing with no distortion in sound quality and good SN ratio.

  In this embodiment, the presence / absence of a clip is determined for the signal added by the adder 34. However, the presence / absence of a clip may also be determined for the signal processed by the DSP power addition processor 33.

  In this embodiment, when a signal with a low level continues, control is performed so that the coefficient is increased by the processing of s3 → s8, s9, and s10. This is suitable for watching a DVD or the like in real time. ing. On the other hand, if you need to fix the coefficient, such as when recording the audio source of analog media to other media, play the audio source once to determine the coefficient, then fix the coefficient and then Play and record the. In this case, the processing of s8, s9, and s10 is not performed in order to determine a (maximum) coefficient that does not clip through the entire source.

Hardware block diagram of a digital audio amplifier according to an embodiment of the present invention Functional block diagram around the DSP of the digital audio amplifier A flowchart showing the operation of the CPU of the digital audio amplifier The figure which shows the example of the control screen of the personal computer which is connected to the same digital audio amplifier The figure which shows the example of the control screen of the personal computer which is connected to the same digital audio amplifier

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Digital audio amplifier, 2 ... Remote control, 3 ... Personal computer, 4 ... Other audio equipment, 5 ... Speaker,
DESCRIPTION OF SYMBOLS 10 ... CPU, 11 ... ROM, 12 ... RAM, 13 ... Flash ROM, 14 ... Display device, 15 ... Panel user interface, 16 ... Remote control receiving part, 17 ... DSP, 18 ... Tuner, 19 ... Audio input control part, 20 ... Audio output control unit, 21 ... USB interface, 22 ... Analog amplifier,
DESCRIPTION OF SYMBOLS 31 ... AD converter, 32 ... Coefficient multiplication part, 33 ... DSP multiplication addition process part, 34 ... Addition part, 35 ... Clip detection part, 36 ... Coefficient calculation part, 37 ... DA converter,
40 ... sound field selection button, 41 ... equalizer screen, 42 ... (software-like) analog volume, 43 ... SETUP button, 44 ... slider (of digital volume)

Claims (4)

A signal input unit for inputting a digital audio signal;
Multiplication means for multiplying an input digital audio signal by a gain parameter;
Detection means for detecting whether or not a clip whose level exceeds the maximum value of the number of sampling bits has occurred in the digital audio signal output from the multiplication means;
Based on the detection contents of the detection means when a predetermined digital audio signal is input, a maximum value of the gain parameter that does not cause clipping through the predetermined digital audio signal is determined, and a gain parameter supplied to the multiplication means is determined. Control means for fixing to the determined value;
Digital audio amplifier with A signal output unit to which a recording device is connected;
The signal input unit inputs the predetermined digital audio signal twice,
Wherein, when said predetermined digital audio signal is input to the first time, indexing the value of the gain parameter based on the detected result of said detecting means, said predetermined digital audio signal is input to the second time The gain parameter supplied to the multiplication means is fixed to the determined value,
2. The digital audio amplifier according to claim 1, wherein the signal output unit outputs the predetermined digital audio signal input for the second time and multiplied by a gain parameter by the multiplying unit to the recording device. Processing means for performing predetermined processing on the digital audio signal output from the multiplication means;
3. The digital audio amplifier according to claim 1, wherein the detection unit detects clip generation of a signal obtained by adding the digital audio signal processed by the processing unit and the input digital audio signal. The control means reduces the value of the gain parameter supplied to the multiplication means in response to the detection means detecting the clip, and when the detection means does not detect the clip continuously for a predetermined time, the multiplication means further digital audio amplifier according to any one of claims 1 to 3 performs a normal mode operation to increase the value of the supplied gain parameters.

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