Patent Publication Number: US-2007121971-A1

Title: Audio mixing device and audio mixing method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2005-347113, filed Nov. 30, 2005, the entire contents of which are incorporated herein by reference.  
     BACKGROUND  
      1. Field  
      One embodiment of the present invention relates to an audio mixing device used, for example, with an optical disk device, and improvement of an audio mixing method.  
      2. Description of the Related Art  
      As is well known, optical disks such as Digital Versatile Discs (DVDs) have been widespread as a digital recording medium in recent years. In addition, high reliability is required for an optical disk device reproducing this kind of optical disk.  
      Further, the DVD standard itself has been developed, and currently, the next generation DVD standard supporting high vision that is referred to as High Definition (HD) DVD or Blu-ray disk has been completed. Since the recording density of the next generation DVD standard is significantly increased over that of the current generation DVD, optical disk devices are also required to enhance their functions.  
      For example, an optical disk device supporting the next generation DVD standard may output a plurality of audio data, while mixing it, which is obtained from an optical disk, a network server, etc. However, the sampling frequency of all audio data needs to be matched for mixing of a plurality of audio data.  
      Thus, currently, the mixing is performed by matching a sampling frequency to the highest sampling frequency among a plurality of audio data, or by matching the sampling frequency of other audio data to one of the sampling frequencies of audio data selected based on the previously specified method.  
      However, in the above-mentioned means, when the sampling frequency of the audio data is to be matched with the sampling frequency, all of the sampling frequencies of the audio data to be mixed need to change their sampling frequency of audio data accordingly, during which time, audio output must be stopped.  
      Jpn. Pat. Appln. KOKAI Publication No. 2-277308 discloses that mixing is performed by converting a plurality of digital signals having different sampling frequencies into a digital signal having the same sampling frequency as a double oversampling digital filter; however, no concrete control method is described, and thus it is not suitable for practical use.  
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.  
       FIG. 1  is a block diagram showing one embodiment of the present invention, which is illustrated for explaining an optical disk device.  
       FIG. 2  is a diagram shown to explain a pickup used for an optical disk device in the same embodiment.  
       FIG. 3  is a block diagram shown to explain a specific example of an audio mixing part of an optical disk device in the same embodiment.  
       FIG. 4  is a flowchart shown to explain an audio mixing operation of an optical disk device in the same embodiment.  
       FIG. 5  is a diagram shown to explain the effects of an audio mixing operation for an optical disk device in the same embodiment. 
    
    
     DETAILED DESCRIPTION  
      Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, an audio mixing device comprising: an input part in which a plurality of audio data is input; a conversion part which converts the sampling frequency of all input audio data; a control part which controls such that the sampling frequency of the input audio data is converted into the preset reference sampling frequency for each conversion part; and a mixing part which mixes all audio data output from the conversion part by converting the sampling frequency into the reference sampling frequency; is provided.  
      The optical disk device associated with this embodiment has a configuration as shown in  FIG. 1  and  FIG. 2 . Regarding an optical disk  11 , although a user data recordable (or rewritable) optical disc or a read-only optical disk is targeted, in this example, it is explained as an optical disk including a recordable (or rewritable) next generation DVD.  
      The recordable or rewritable optical disk  11  includes, for example, a next generation DVD-RAM (Random Access Memory) using a blue laser beam with a wavelength of around 405 nm, DVD-RW (Rewritable), DVD-R (Recordable), etc., or current DVD-RAM, DVD-RW, DVD-R, etc. using a red laser beam with a wavelength of around 650 nm.  
      A land track and a groove track are spirally formed on the surface of the optical disk  11 . This optical disk  11  is rotating-driven by a spindle motor  12 . The rotating speed of this spindle motor  12  is controlled by a motor control circuit  13 .  
      Recording and reproducing of information for the optical disk  11  are performed with a pickup  14 . The pickup  14  is connected to a thread motor  15  through a gear. This thread motor  15  is controlled by a thread motor driver  17  connected to a data bus  16 . A permanent magnet (not shown) is provided in the fixed portion of the thread motor  15 . The pickup  14  is moved in the radial direction of the optical disk  11  by exciting a drive coil (not shown).  
      An object lens  18  is provided in the pickup  14  as shown in  FIG. 2 . The object lens  18  is movable in the focusing direction (optical axis direction of the lens) by driving with a drive coil  19 , and is also movable in the tracking direction (orthogonal direction to the optical axis of the lens) by driving a drive coil  20 , which can be track-jumped by moving the beam spot of a laser beam.  
      A modulation circuit  21  performs, for example, 8-14 modulation (Eight to Fourteen Modulation: FEM) for user data supplied from a host device  22  through an interface circuit  23  at information recording to generate EFM data. A laser control circuit  24  provides a writing signal to a semiconductor laser diode  25  based on EFM data supplied from the modulation circuit  21  at information recording (at mark forming).  
      In addition, the laser control circuit  24  provides the semiconductor laser diode  25  with a reading signal that is smaller than a writing signal at information reading.  
      The semiconductor laser diode  25  generates a laser beam in response to a writing signal supplied from laser control circuit  24 . The laser beam emitted from the semiconductor diode  25  is irradiated on the optical disk  11  through a collimating lens  26 , a half prism  27 , an optical system  28 , and the object lens  18 . Reflected light from the optical disk  11  is led to a photodetector  30  through the object lens  18 , the optical system  28 , the half prism  27 , and a condensing lens  29 .  
      The photodetector  30  comprises a photodetection cell divided in four, and supplies signals A, B, C, and D to a Radio Frequency (RF) amplifier  31 . The RF amplifier  31  supplies, for example, a tracking error signal TE corresponding to (A+D)−(B+C) to a tracking control part  32  by employing a push-pull method, and supplies, for example, a focus error signal FE corresponding to (A+C)−(B+D) to a focusing control part  33  by employing an astigmatism method.  
      Further, the RF amplifier  31  supplies, for example, a wobble signal WB corresponding to the (A+D)−(B+C) to a wobble PLL part/address detecting part  34 , and supplies a RF signal corresponding to (A+D)+(B+C) to a data reproducing part  35 .  
      The output signal of the focusing control part  33  is supplied to the drive coil  19  of the focusing direction. Thus, the laser beam is controlled so that it is always focused only on the recording film of the optical disk  11 . In addition, the tracking control part  32  generates a track driving signal in response to the tracking error signal TE, which is supplied to the drive coil  20  of the tracking direction.  
      By performing the above-mentioned focusing control and tracking control, the change of reflectivity from a pit, etc. formed on a track of the optical disk  11  in response to recorded information is reflected on a sum signal RF of output signals from the photodetection cell of the photodetector  30 . This signal is supplied to a data reproducing part  35 .  
      The data reproducing part  35  reproduces recorded data based on a reproducing clock signal from a PLL circuit  36 . In addition, the data reproducing part  35  comprises a function to measure the amplitude of the signal RF, and the measured value is read by a Central Processing Unit (CPU)  37 .  
      The pickup  14  is controlled by the thread motor  15  being controlled so that the object lens  18  is placed at the optimum position of the optical disk  11 , when the object lens  18  is controlled by the tracking control part  32 .  
      The motor control circuit  13 , the laser control circuit  24 , the focusing control part  33 , the tracking control part  32 , the data reproducing part  35 , the PLL circuit  36 , etc., can be composed on one LSI chip as a servo control circuit.  
      In addition, these circuit parts are controlled by the CPU  37  through the bus  16 . The CPU  37  controls this optical disk device comprehensively based on an operational command supplied from the host device  22  through the interface circuit  23  or operation information from an operation part (not shown).  
      Further, the CPU  37  uses a RAM  38  as an operation area, which performs a prescribed operation in accordance with a program recorded on a Read-only Memory (ROM)  39 .  
      Then, data reproduced in the data reproducing part  35  is provided for reproducing an image, a secondary image, and audios after error correction is conducted on the data by an error correcting circuit  40 .  
      Wherein, an audio mixing part  41  is connected to the bus  16 . This audio mixing part  41  enables outputting a plurality of digital audio data to the exterior of the optical disk device with the mixing. The plurality of digital audio data includes the digital audio data reproduced from the optical disk  11  and the digital audio data obtained from an external network server through the interface circuit  23 .  
       FIG. 3  shows a specific example of the audio mixing part  41 . That is, this audio mixing part  41  comprises a plurality of (there are three in the figure) audio input terminals  41   a ,  41   b , and  41   c.    
      In addition, this embodiment is explained assuming that audio data that becomes main audio reproduced from the optical disk  11  is supplied to the audio input terminal  41   a , audio data that becomes sub-audio obtained from an external network server is supplied to the audio input terminal  41   b , and audio data that becomes effect audio obtained from, for example, an external network server is supplied to the audio input terminal  41   c.    
      In the next generation DVD standard, three kinds of sampling frequencies (48, 96, and 192 kHz) of audio data that becomes main audio are specified, and three kinds of sampling frequencies (12, 24, and 48 kHz) of audio data that becomes sub-audio and effect audio are specified, respectively.  
      Then, the audio data supplied to the audio input terminal  41   a  is supplied to a sampling frequency conversion part  41   d . This sampling frequency conversion part  41   d  performs conversion of the sampling frequency for audio data to be input, output stop of audio data during conversion, and so on based on the control of a mixing control part  41   g.    
      Then, the audio data supplied to the audio input terminal  41   b  is supplied to a sampling frequency conversion part  41   e . This sampling frequency conversion part  41   e  executes conversion of the sampling frequency for audio data to be input, output stop of audio data during conversion, and so on based on the control of a mixing control part  41   g.    
      Then, the audio data supplied to the audio input terminal  41   c  is supplied to a sampling frequency conversion part  41   f . This sampling frequency conversion part  41   f  executes conversion of sampling frequency for audio data to be input, output stop of audio data during conversion, and so on based on the control of a mixing control part  41   g.    
      Wherein, the mixing control part  41   g  selectively controls each sampling frequency conversion part  41   d ,  41   e , and  41   f  based on a control signal from the CPU  38  supplied through a control terminal  41   h.    
      That is, the mixing control part  41   g  controls sampling frequency conversion so that the sampling frequency of audio data to be input becomes a preset reference sampling frequency (e.g., 96 kHz) for each sampling frequency conversion part  41   d ,  41   e , and  41   f.    
      In this case, when the sampling frequency of audio data to be input is changed for each sampling frequency conversion part  41   d ,  41   e , and  41   f , the mixing control part  41   g  controls so that it converts the changed sampling frequency to the reference sampling frequency; however, it controls to stop the output of audio data during conversion, and to resume outputting audio data after the change to the reference sampling frequency is completed.  
      Then, all audio data having the reference sampling frequency output from each sampling frequency conversion part  41   d ,  41   e , and  41   f  is supplied to a mixing part  41   i  to conduct mixing, and is led externally from an audio output terminal  41   j.    
      In the above-mentioned configuration, the audio mixing operation will now be explained with reference to the flowchart shown in  FIG. 4 . That is, when this operation is started (block S 1 ), CPU  37  sets the reference sampling frequency in block S 2 .  
      This reference sampling frequency may be preset fixedly, or may be set, if desired, in consideration of the amount of audio data to be processed and the processing capacity of the audio mixing part  41 . In addition, it may also be possible that a plurality of reference sampling frequency types are prepared in advance so that a user can select any of the reference sampling frequency types.  
      Next, in block S 3 , CPU  37  obtains the sampling frequency of all audio data to be mixed, that is, all audio data supplied to the audio input terminal  41   a ,  41   b , and  41   c . This information can be obtained from information of an image and audio obtained from a network server or obtained from management information and information of an image and audio recorded on the optical disk  11 .  
      Then, in block S 4 , CPU  37  calculates a conversion rate to convert the sampling frequency into the reference sampling frequency for all audio data supplied to the audio input terminals  41   a ,  41   b , and  41   c  respectively, and supplies it to the mixing control part  41   g . When the reference sampling frequency is 96 kHz and the sampling frequency of audio data is 48 kHz, this conversion rate is calculated as 96/48=2.  
      Then, in block S 5 , the mixing control part  41   g  sets the conversion rate for all audio data supplied from CPU  37  to the corresponding sampling frequency conversion parts  41   d ,  41   e , and  41   f  respectively. Thereby, each sampling frequency conversion part  41   d ,  41   e , and  41   f  convert the input sampling frequency of the audio data into the reference sampling frequency to output.  
      In this case, if the conversion rate is 2 as described above, upsampling that doubles the sampling frequency of the audio data is performed. Whereas, if the reference sampling frequency is lower than the sampling frequency of the audio data, since the conversion rate will be zero to one, downsampling that lowers the sampling frequency of the audio data will be performed.  
      And, when the audio data that is converted into the reference sampling frequency is output from each sampling frequency conversion part  41   d ,  41   e , and  41   f , in block S 6 , the mixing part  41   i  outputs all audio data with mixing, and thus audio reproduction is started.  
      Then, in block S 7 , CPU  37  determines whether the audio reproduction is completed, and when it is determined that it is finished (YES), the audio mixing operation is finished (block S 13 ).  
      However, in block S 7 , when it is determined that the audio reproduction is not finished (NO), in block S 8 , CPU  37  determines whether there is any change in the sampling frequency of all audio data supplied to the audio input terminal  41   a ,  41   b , and  41   c . This determination can be performed based on information indicating the sampling frequency of all audio data explained in block S 3  previously.  
      And, in block S 8 , when it is determined that there is no change in the sampling frequencies of all audio data (NO), CPU  37  returns to the process in block s 7 .  
      However, in block S 8 , when it is determined that there is change in any of the sampling frequencies of all audio data (YES), in block S 9 , CPU  37  controls the mixing control part  41   g  so that the audio data in which the sampling frequency is changed is excluded from the mixing target. Thereby, the mixing control part  41   g  controls so that the sampling frequency conversion part  41   d ,  41   e , or  41   f  corresponding to the audio data in which the sampling frequency is changed stops the output of audio data.  
      Next, in block S 10 , CPU  37  obtains information indicating the sampling frequency, and calculates a conversion rate to convert the sampling frequency into the reference sampling frequency for the audio data in which the sampling frequency is changed, and supplies it to the mixing control part  41   g.    
      Then, in block S 11 , the mixing control part  41   g  set the conversion rate supplied from CPU  37  to the corresponding sampling frequency conversion parts  41   d ,  41   e ,  41   f  respectively. Thereby, corresponding sampling frequency conversion parts  41   d ,  41   e , and  41   f  convert the input sampling frequency of the audio data into the reference sampling frequency to output.  
      Then, in block S 12 , CPU  37  controls the mixing control part  41   g  so that the audio data converted into the reference sampling frequency is a mixing target, and shifts to the process in block S 7 . Thereby, the mixing control part  41   g  controls so that it cancels the output stop of the audio data for corresponding sampling frequency conversion part  41   d ,  41   e , or  41   f , and thus the audio data is mixed.  
      The effects of the above-mentioned audio mixing operation are explained in detail with reference to  FIG. 5 . In  FIG. 5 , the audio data which is supplied to the audio input terminal  41   a  is referred to as the first audio data, the audio data which is supplied to the audio input terminal  41   b  is referred to as the second audio data, and the audio data which is supplied to the audio input terminal  41   c  is referred to as the third audio data.  
      It is assumed that the reference sampling frequency is set to 96 kHz, and before time t 1 , the sampling frequency of the first audio data is 48 kHz, the sampling frequency of the second audio data is 12 kHz, and the sampling frequency of the third audio data is 12 kHz.  
      In this case, the first audio data is double upsampled with the sampling frequency conversion part  41   d  and is converted into the reference sampling frequency. The second audio data is eightfold upsampled with the sampling frequency conversion part  41   e  and is converted into the reference sampling frequency. The third audio data is eightfold upsampled with the sampling frequency conversion part  41   f  and is converted into the reference sampling frequency.  
      In the above-mentioned state, it is assumed that the sampling frequency of the second audio data is changed to 24 kHz at time t 1 . In this process, the output of the second audio data is stopped by the sampling frequency conversion part  41   e , and then it is output after being fourfold upsampled and converted into the reference sampling frequency.  
      That is, the second audio data is not output during processing to convert the changed sampling frequency into the reference sampling frequency, and meanwhile, the first and third audio data are continuously output. Consequently, the output of the mixed audio data is continued, and thereby, stopping of the audio output can be prevented.  
      In addition, it is assumed that the sampling frequency of the third audio data is changed to 48 kHz at time t 2 . In this process, the output of the third audio data is stopped by the sampling frequency conversion part  41   f , and then it is output after being double upsampled and converted into the reference sampling frequency.  
      That is, the third audio data is not output during processing to convert the changed sampling frequency into the reference sampling frequency, and meanwhile, the first and second audio data are continuously output. Consequently, the output of the mixed audio data is continued, and thereby, stopping of the audio output can be prevented.  
      Further, it is assumed that the sampling frequency of the second audio data is changed to 48 kHz at time t 3  and the sampling frequency of the third audio data is simultaneously changed to 24 kHz. In this process, the output of the second audio data is stopped by the sampling frequency conversion part  41   e , and then it is output after being double upsampled and converted into the reference sampling frequency. Moreover, the output of the third audio data is stopped by the sampling frequency conversion part  41   f , and then it is output after being fourfold upsampled and converted into the reference sampling frequency.  
      That is, the second and third audio data are not output during processing to convert the changed sampling frequency into the reference sampling frequency, and meanwhile, the first audio data is continuously output. Consequently, the output of the mixed audio data is continued, and thereby, stopping of the audio output can be prevented.  
      However, as shown at time t 4 , when the sampling frequencies of the first to the third audio data are simultaneously changed, since the first to the third audio data are not output while they are converted into the reference sampling frequency in the sampling frequency conversion part  41   d  to  41   f , only in this case, the audio output is stopped. However, since it is a rare possibility that the sampling frequencies of the first to the third audio data are simultaneously changed, there is no problem with practical use.  
      According to the above-mentioned embodiment, since it is intended to match the sampling frequency of the first to the third audio data to be mixed to the preset reference sampling frequency, if any of the sampling frequencies of the audio data are changed, the output of the other audio data is continued, and thus, stopping of the audio output can be prevented as much as possible.  
      In addition, in the above-mentioned embodiment, although the number of the audio data to be mixed is of three kinds, it is not limited to this, and the present invention can also be applied in the case of mixing of four or more kinds of audio data.  
      While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.