JP5002414B2 - Hearing sensitivity correction device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out band division of an audio signal without changing a cut-off frequency, reduce interference at a composite time of the divided audio signals, and add suitable loudness characteristics. <P>SOLUTION: A hearing sense correction apparatus 1 is provided with: a plurality of respective band filters 5 to 8 for dividing an audio signal into respective bands; a gain adjustment means 11, 12 to perform gain correction on the audio signal filter-processed by the respective band filters 5 to 8; filter means 3, 4 with composite processing means 15, 16 which perform composite processing of respective audio signals subjected to gain adjustment 11, 12; and a gain calculation means 2 which calculates gain values adjusted in the gain adjustment means 11, 12 for respective band filters 5 to 8. Filter characteristics of the respective band filters 5 to 8 are set so as not to generate interference when the audio signals filter-processed are composed. The gain calculation means 2 distributes the gain values for respective band kinds according to a number of installation of the filter means 3, 4. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an auditory sensitivity correction apparatus, and more particularly, to an auditory sensitivity correction apparatus that can add a loudness characteristic to an audio signal by combining the audio signal after filtering by band.

  A general audio playback device is provided with a volume control unit for adjusting the volume output from the speaker, and the user preferably adjusts the volume output from the speaker or the like by operating the volume control unit. It is possible to adjust.

  However, with a general volume control unit, the volume can be adjusted only by a certain amount (for example, about +6 dB to 12 dB), and a sound quality with sufficient loudness characteristics can be obtained when further adjustment is necessary. However, there is a problem that the request cannot be satisfied by operating the volume control unit.

In order to satisfy such a requirement, a loudness control device (auditory sensitivity correction device) that corrects auditory sensitivity with respect to the volume of output sound has been proposed (see, for example, Patent Document 1). The loudness control device divides the audio signal into low, mid, and high frequencies, and changes the gain of the low, mid, and high frequencies in conjunction with the amount of operation of the volume control unit. Signals are synthesized and output from a speaker or the like, and auditory sensitivity correction is performed.
JP 2000-197182 A (page 4-5, FIG. 1)

  By the way, in the above-described loudness control device, when signals for each of the divided sound ranges are combined, signal interference occurs due to a phase difference between the bands, and dip (distortion) occurs in the wavelength of the combined signal. There can be. When such a dip occurs, the above-described loudness control apparatus performs a process of smoothing the loudness characteristic by changing the cutoff frequency of the filter in accordance with the correction level.

  However, in order to change the cut-off frequency of the filter according to the level, it is necessary to provide a plurality of filter coefficients in the loudness control device, and thus there is a problem that means for storing a large amount of coefficient data is required. there were.

  In addition, when an IIR (infinite impulse response) filter is used as the band division filter, if the filter coefficient is changed while the audio signal is reproduced, the acoustic processing operation becomes unstable due to the coefficient changing during the feedback operation. There was a risk that the sound would be heard or an abnormal noise would occur.

  The present invention has been made in view of the above problem, and performs a band division by applying a filter process to an audio signal without changing a cutoff frequency, and synthesizes an audio signal for each divided band. It is an object of the present invention to provide an auditory sensitivity correction apparatus capable of adding a suitable loudness characteristic to output sound by reducing interference of signals in each band.

  In order to solve the above-described problems, an auditory sensitivity correction apparatus according to the present invention includes a plurality of band-by-band filters for dividing an audio signal for each band, and an audio signal divided for each band by the plurality of band-by-band filters. Are adjusted by the gain adjusting means, a filter means having a gain adjusting means for adjusting the gain for each audio signal, a synthesizing processing means for synthesizing each audio signal subjected to the gain adjustment, and the gain adjusting means. Gain calculating means for calculating a gain value for each band-based filter in accordance with a signal level of an audio signal or a volume level set by a user, and the band-by-band filter is filtered by each band-by-band filter. When the audio signal is synthesized by the synthesis processing means, no interference occurs in the synthesized audio signal. Filter characteristics of each band-specific filter are set, a plurality of the filter means are provided, the plurality of filter means are cascade-connected, and the gain calculating means is in accordance with the number of installed filter means to be cascade-connected. The gain value adjusted for each band-by-band filter is distributed for each band type of the band-by-band filter.

  According to the auditory sensitivity correction apparatus of the present invention, when the filter characteristics of the band-by-band filters provided in the filter unit combine the audio signals filtered by the band-by-band filters by the synthesis processing unit, interference between signals Is set so as not to occur, it is possible to suppress the interference of the signal subjected to the loudness correction. For this reason, it is possible to add an optimal loudness effect to the audio signal without causing any trouble such as distortion or noise in the sound.

  In addition, by considering (changing) the acoustic correction characteristics of each filter unit and connecting the respective filter units in combination by cascade connection, the cutoff frequency of the band-by-band filter as in the conventional loudness control device Thus, a smooth loudness characteristic can be added to the audio signal without changing the value. Further, since it is not necessary to vary the cutoff frequency individually, it is not necessary to store a large number of coefficient data.

  Furthermore, since the gain calculation means distributes and adjusts the gain value for adding the loudness effect according to the volume level or the level of the audio signal, the optimum and effective loudness according to the volume level or the level of the audio signal. The correction can be added to the audio signal, and music with good sound quality (loudness characteristics) can be provided to the listener.

  In particular, when an audio signal filtered using the band-by-band filter according to the present invention is synthesized, no interference occurs in the signal. For this reason, the gain calculation means distributes the gain value for each band type according to the number of installed filter means, thereby enabling effective gain adjustment without causing interference or the like during synthesis. As a result, an optimum loudness effect can be added to the audio signal.

  Moreover, it is preferable to use a high-pass filter or a low-pass filter that is a first-order IIR filter as the band-by-band filter of the above-described auditory sensitivity correction device.

  As described above, when a high-pass filter or a low-pass filter that is a first-order IIR filter is used as the band-by-band filter, the phase of the audio signal that has been subjected to the filter processing by the high-pass filter and the low-pass filter is kept within ± 90 degrees. Is possible. For this reason, even if the audio signals filtered by the respective filters are synthesized, it is possible to suppress the occurrence of interference in the synthesized audio signal, and a smooth loudness characteristic can be added to the audio signal.

  Furthermore, it is preferable to use a peaking filter that is a secondary IIR filter as the band-by-band filter of the above-described auditory sensitivity correction apparatus.

  As described above, when the peaking filter is used as the filter for the specific band of the band-specific filter, the audio signal subjected to the filtering process using the peaking filter and the filter for other bands, for example, the primary IIR Even when the audio signal that has been filtered by a high-pass filter or low-pass filter as a filter is synthesized, the occurrence of interference in the synthesized audio signal can be suppressed, and the audio signal is smooth. It becomes possible to add a loudness characteristic.

  In the loudness control apparatus according to the present invention, the filter characteristics of the band-by-band filters are set so that interference between signals does not occur when the audio signals filtered by the band-by-band filters are synthesized by the synthesis processing means. ing. For this reason, by using the auditory sensitivity correction device, it is possible to suppress the interference of the signal subjected to the loudness correction, and to add the optimum loudness effect to the audio signal without causing any distortion or noise in the sound. It becomes possible.

  Further, since the audio signal is subjected to loudness correction by connecting a plurality of filter means by cascade connection, the filter means is combined by considering (changing) the frequency characteristics of each filter means and combining the filter means. It is possible to perform a suitable loudness correction on the audio signal without changing the cutoff frequency every time.

  Furthermore, since the gain calculation means distributes and adjusts the gain value for adding the loudness effect according to the volume level or the level of the audio signal, the optimum and effective loudness according to the volume level or the level of the audio signal. The correction can be added to the audio signal, and music with good sound quality (loudness characteristics) can be provided to the listener.

  The hearing sensitivity correction apparatus according to the present invention will be described below.

  FIG. 1 is a block diagram showing a schematic configuration of an auditory sensitivity correction apparatus. The auditory sensitivity correction apparatus 1 includes a gain calculation unit (gain calculation unit) 2 and a plurality of cascaded loudness filter units (filter units) 3 and 4. In the auditory sensitivity correction apparatus 1 shown in the present embodiment, for the sake of convenience of explanation, a case where two loudness filter units 3 and 4 are connected as shown in FIG. 1 will be described as an example. The number is not limited to two, but may be configured by connecting three or more loudness filter units.

  The loudness filter units 3 and 4 are, as loudness filters, for performing gain adjustment on primary or secondary IIR filters (band-specific filters) 5 to 8 and audio signals filtered by the respective filters. The integrators (gain adjusting means) 11 to 14 and adders 15 (synthesizing means) 15 and 16 for synthesizing the audio signals whose gains have been adjusted in the integrators 11 to 14 are configured.

  Specifically, when a first-order IIR filter is used as the loudness filter, a low-pass filter (hereinafter referred to as “LPF”) or a high-pass filter (hereinafter referred to as “HPF”) is used. In the case where a secondary IIR filter is used, a peaking filter is applied.

  When LPF or HPF is used as the first-order IIR filter, or when a peaking filter is used as the second-order IIR filter, the phase change of the filtered audio signal in each band is within ± 90 degrees at the maximum. Can fit. Therefore, even when gains of respective bands (for example, a low frequency band and a high frequency band) are synthesized for all frequencies, there is a feature that the possibility of causing interference in the synthesized audio signal is low.

  For example, when a primary IIR filter is used as the loudness filter of the loudness filter unit 3, an LPF (for example, a Butterworth filter) 5 having a cutoff frequency of 90 Hz, and an HPF (for example, a Butterworth filter) 6 having a cutoff frequency of 9 kHz, FIG. 2 shows the amplitude characteristics of the filter and FIG. 3 shows the phase characteristics when the gain is set to 10 dB.

  In this way, when LPF5 or HPF6 is used as the first-order IIR filter and the phase characteristics of the frequency for each band and the synthesized frequency are determined from FIG. The phase difference is within ± 90 degrees, and even if the frequencies of the respective bands are synthesized, as is clear from the amplitude characteristics shown in FIG. Can be synthesized. Therefore, by considering (adjusting / changing) the filter characteristics of the LPF 5 and the HPF 6 in accordance with the desired loudness characteristics and combining the gains of the respective bands, a suitable loudness characteristic can be obtained with almost no interference. It becomes possible.

  In the auditory sensitivity correction apparatus 1 according to the present invention, a filter characteristic that can be synthesized without interference even when the frequencies of the respective bands are synthesized is used as a loudness filter. For this reason, a filter having a filter characteristic that causes interference when the frequencies of the respective bands are combined cannot be used as a loudness filter.

  For example, as a secondary IIR filter, an LPF with a cutoff frequency of 90 Hz (for example, a Butterworth filter) and an HPF with a cutoff frequency of 9 kHz (for example, a Butterworth filter) are used, and the gain of each filter is 10 dB. The amplitude characteristic is shown in FIG. 4, and the phase characteristic is shown in FIG.

  Looking at the phase characteristics shown in FIG. 5, the phase difference between the low and high frequencies is ± 180 degrees at the maximum, and by synthesizing the frequencies of each band, it is clear from the amplitude characteristics shown in FIG. A dip due to interference occurs. As described above, when LPF and HPF are used in the secondary IIR filter, the phase difference becomes ± 90 degrees or more. Therefore, when the secondary IIR filter is used, a peaking filter is used. By using the peaking filter as a secondary IIR filter, it is possible to avoid interference of the synthesized frequency.

  For example, when a second-order IIR filter is used as the loudness filter of the loudness filter unit 4, the low frequency is centered by using the peaking filter 7 having a center frequency of 40 Hz and a selectivity Q of 1, as shown in FIG. It is possible to perform the filtering process. In the present embodiment, the peaking filter 7 is used as a low-pass filter centered on a low-frequency, but the peaking filter is not necessarily limited to use as a low-pass filter. It can also be used as a filter for a high frequency band or a high frequency band.

  Furthermore, in the auditory sensitivity correction apparatus 1 according to the present embodiment, a primary IIR filter is used as the loudness filter of the loudness filter unit 4 in addition to the peaking filter 7 described above. Fig. 5 shows the amplitude characteristics of a filter when an HPF (for example, a Butterworth filter) 8 having a cutoff frequency of 12 kHz is used as a primary IIR filter and a gain for the peaking filter 7 and the HPF 8 is 10 dB. It is shown in FIG. FIG. 7 shows a total loudness characteristic in which the above-described loudness filter unit 3 and loudness filter unit 4 are cascade-connected.

  As described above, in the loudness filter unit 3, interference of the synthesized frequency can be prevented by using the LPF 5 and the HPF 6 as the primary IIR filter, and in the loudness filter unit 4, By using the peaking filter 7 as the IIR filter and using the HPF 8 as the primary IIR filter, it is possible to prevent interference of the synthesized frequency.

  Further, by connecting the loudness filter unit 3 and the loudness filter unit 4 capable of preventing interference by cascade connection, and synthesizing the frequencies of the audio signals filtered by the respective loudness filter units 3 and 4, As a whole, a desired loudness characteristic can be obtained with almost no interference.

  In particular, parameters such as the cut-off frequency of each of the loudness filter units 3 and 4 can be arbitrarily set independently in advance. Therefore, by appropriately setting the parameters, a desired loudness characteristic can be easily and easily set. It can be obtained effectively.

  In the present embodiment, the case where the auditory sensitivity correction apparatus 1 is configured by cascading two loudness filter units 3 and 4 will be described. However, the above-described interference can be prevented. A more effective loudness characteristic can be obtained by cascading a plurality of (three or more) loudness filter units.

  Next, the gain calculation unit 2 will be described. The gain calculation unit 2 calculates a low-frequency gain and a high-frequency gain of the signal according to the volume level of a volume adjustment unit (not shown) set and operated by the user or according to the level of the audio signal. Have a role to play.

  FIG. 8 shows a gain correction amount calculated according to the volume level adjusted by the volume adjustment unit and the level of the audio signal. As shown in FIG. 8, when the level is 0 dB, the gain of each filter unit is 0 dB for both low and high frequencies, and when the level is −30 dB, the low frequency gain is 24 dB and the high frequency gain. The gain correction (gain adjustment) is performed so that becomes 20 dB.

  The gains of the band-by-band filters that have been gain-corrected as shown in FIG. 8 are distributed in correspondence with the number of band-by-band filters that are set, and correction processing is performed by the integrators 11 and 12 shown in FIG. Done. For example, as shown in the present embodiment, when two loudness filter units 3 and 4 are connected, the high-pass filters (HPF6 and HPF8) and the low-pass filters (LPF5 and The corrected gain is distributed evenly to the peaking filter 7).

  When the level is −30 dB, as shown in FIG. 8, the low-frequency gain is 24 dB and the high-frequency gain is 20 dB. For this reason, when these gains are evenly distributed, the correction gains of the low-pass filters (LPF5 and peaking filter 7) are 12 dB, and the correction gains of the high-pass filters (HPF6 and HPF8) are 10 dB. It becomes.

  Under these conditions, white noise and pink noise are set as audio signals, and the output frequency characteristics of the auditory sensitivity correction apparatus 1 when the noise levels are set to 0 dB, −12 dB, −24 dB, and −36 dB are shown in FIG. 10, 11, and 12.

  FIG. 9 shows frequency characteristics of white noise that is not subjected to loudness correction using the auditory sensitivity correction apparatus 1, and FIG. 10 shows frequency characteristics of white noise that is subjected to loudness correction using the auditory sensitivity correction apparatus 1. Is shown. FIG. 11 shows the frequency characteristics of pink noise that is not subjected to loudness correction using the auditory sensitivity correction apparatus 1, and FIG. 12 is the pink noise frequency characteristic that is subjected to loudness correction using the auditory sensitivity correction apparatus 1. The frequency characteristics are shown.

  As is apparent from the frequency characteristics shown in FIGS. 9 to 12, by correcting the audio signal using the auditory sensitivity correction apparatus 1, a low frequency gain and a high frequency gain are obtained according to each band. And the combined audio signal can be prevented from interfering with each other, and a loudness effect can be added without causing a dip in the signal.

  As described above, in the auditory sensitivity correction apparatus 1 according to the present embodiment, the auditory sensitivity correction apparatus 1 is configured by a plurality of cascaded loudness filter units 3 and 4, and each loudness filter unit 3 and 4 is A plurality of loudness filters 5 to 8 for performing filter processing for each different band are provided, and a filter that does not cause interference even when the audio signals of the respective filtered bands are combined is used as the loudness filter. As a result, it is possible to add an optimum loudness effect to the audio signal without causing any distortion or noise in the sound.

  In addition, by distributing and adjusting the gain for adding the loudness effect according to the volume level of the volume control unit or the level of the audio signal, the optimum loudness correction according to the level of the volume control unit or the audio signal level Thus, it is possible to provide music with a good sound quality (loudness characteristic) to the listener.

  The auditory sensitivity correction apparatus according to the present invention has been described in detail with reference to the drawings. However, the auditory sensitivity correction apparatus according to the present invention is not limited to the above-described embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the auditory sensitivity correction apparatus 1 shown in the present embodiment, a low-pass filter and a high-pass filter are first-order IIR filters as the loudness filter of the loudness filter unit 3, and the loudness filter of the loudness filter unit 4 is used. The secondary IIR filter is used as the low-pass filter and the primary IIR filter is used as the high-pass filter. The combination of the high-pass filter and the low-pass filter is the combination according to the above-described embodiment. It is not limited. For example, the low-pass filter of the loudness filter unit 4 may use a combination of an LPF as a primary IIR filter and a high-pass filter using a peaking filter as a secondary IIR filter. Furthermore, the filter used for the loudness filter unit is not necessarily limited to the IIR filter, and an FIR filter or the like may be used.

It is the block diagram which showed schematic structure of the auditory sensitivity correction apparatus which concerns on this Embodiment. A first-order IIR filter is used as a loudness filter according to the present embodiment, an LPF with a cut-off frequency of 90 Hz and an HPF with a cut-off frequency of 9 kHz are used, and the amplitude characteristics of the filter are each 10 dB. FIG. Using a first-order IIR filter as a loudness filter according to the present embodiment, using an LPF with a cut-off frequency of 90 Hz and an HPF with a cut-off frequency of 9 kHz, and a gain of 10 dB respectively, the phase characteristics of the filter FIG. It is the figure which showed the amplitude characteristic of the filter when using a secondary IIR filter as a loudness filter, using LPF with a cut-off frequency of 90 Hz and HPF with a cut-off frequency of 9 kHz, and setting the gain to 10 dB. It is the figure which showed the phase characteristic of the filter at the time of using a secondary IIR filter as a loudness filter, using LPF with a cut-off frequency of 90 Hz and HPF with a cut-off frequency of 9 kHz, and setting the gain to 10 dB. A second-order IIR filter as a loudness filter, using a peaking filter 7 having a center frequency of 40 Hz and a selectivity Q of 1 as a low-pass filter, and a first-order IIR filter having an cutoff frequency of 12 kHz HPF. It is a figure which shows the amplitude characteristic of a filter when it uses as a filter for high regions, and a gain is 10 dB, respectively. It is the figure which showed the total loudness characteristic at the time of connecting the loudness filter part 3 and the loudness filter part 4 which concern on this Embodiment in cascade. In the gain calculation part which concerns on this Embodiment, it is the figure which showed the gain correction amount calculated according to the level adjusted in a volume adjustment part, and the level of an audio signal. The frequency characteristic of the white noise which has not performed the loudness correction using the auditory sensitivity correction apparatus according to the present embodiment is shown. The frequency characteristic of the white noise which performed the loudness correction using the auditory sensitivity correction apparatus which concerns on this Embodiment is shown. The frequency characteristic of the pink noise which has not performed the loudness correction using the auditory sensitivity correction apparatus according to the present embodiment is shown. The frequency characteristic of the pink noise which performed the loudness correction | amendment using the auditory sensitivity correction apparatus which concerns on this Embodiment is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Auditory sensitivity correction apparatus 2 ... Gain calculation part (gain calculation means)
3, 4 ... Loudness filter section (filter means)
5 ... LPF (band-based filter, low-pass filter)
6, 8 ... HPF (band-based filter, high-pass filter)
7 ... Peaking filter (band-based filter)
11-14 ... integrator (gain adjustment means)
15, 16 ... Adder (combining processing means)

Claims (3)

A plurality of band-by-band filters for dividing the audio signal into bands;
Gain adjusting means for performing gain adjustment for each audio signal with respect to the audio signal divided for each band by the plurality of band-by-band filters;
Filter means having synthesis processing means for synthesizing each audio signal for which gain adjustment has been performed;
Gain calculating means for calculating a gain value adjusted by the gain adjusting means for each filter according to the band according to a signal level of an audio signal or a volume level set by a user;
The band-by-band filter has a filter characteristic of each band-by-band filter so that interference does not occur in the synthesized audio signal when the audio signal filtered by the band-by-band filter is synthesized by the synthesis processing means. ,
A plurality of the filter means are provided, and the plurality of filter means are cascade-connected,
The gain calculating means distributes the gain value adjusted for each band-by-band filter according to the number of the filter means installed in cascade, for each band type of the band-by-band filter. Sensitivity correction device.   The auditory sensitivity correction apparatus according to claim 1, wherein a high-pass filter or a low-pass filter is used as the first-order IIR filter for the band-by-band filter.   The hearing sensitivity correction apparatus according to claim 1, wherein a peaking filter is used as the secondary IIR filter for the band-by-band filter.

Images