JPH0923127A - High frequency compensating device for audible sound signal and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency compensating device and its method capable of virtually compensating the high frequency of a sound signal of which frequency band is limited. SOLUTION: An analog sound outputted from an analog sound source 11 of which upper limit frequency is limited to 8kHz is sampled by an A/D converter 123 in a processing part at 16kHz corresponding to twice the upper limit frequency and the sampled signal is fetched as a digital signal. So-called zero order interpolation is applied to the center of the digital signal to obtain a 32kHz digital signal and low pass filtering processing for the 32kHz digital signal is executed. After applying envelope processing to a prescribed characteristic, the digital signal is restored to an analog sound at 32kHz through a D/A converter 124 and the analog sound is outputted from a speaker 14 through an amplifier 13. Consequently virtual high frequency compensation for a sound signal of which frequency band is limited can be attained by the processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audible audio signal high frequency compensating apparatus and apparatus, and more particularly to a high frequency compensating apparatus and method for performing virtual high frequency compensation for an audible audio signal whose frequency band is limited. Regarding

[0002]

2. Description of the Related Art Digital audio processing used in CDs and the like is currently widely used because it does not cause deterioration of sound quality during recording, duplication and reproduction of audio signals.

[0003]

However, since the frequency is limited to a predetermined band in digital voice processing,
Out-of-band high-frequency audible audio is removed. Therefore, it is inevitable that a shortage of high frequencies will occur during reproduction. The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-frequency compensating apparatus and method capable of virtually performing high-frequency compensation on an audible audio signal having a limited frequency band. And

[0004]

According to a first aspect of the present invention, there is provided a high frequency compensating device for an audible audio signal, wherein an analog signal whose band is limited at a predetermined upper limit frequency is output at an integer multiple of 2 or more of the predetermined upper limit frequency. A sampling means for sampling at a certain sampling frequency and converting it into a digital signal, and a digital signal output from the sampling means are interpolated at an interpolation frequency which is a frequency that is an integer multiple of 2 or more of the sampling frequency, and an interpolated digital signal is output. An interpolating means, a removing means for removing a frequency band component having a frequency higher than a sampling frequency of the interpolating digital signal output from the interpolating means to output a low-frequency digital signal, and an envelope of the low-frequency digital signal output from the removing means are predetermined. Equalizer means for forming a digital envelope signal by shaping it into an envelope of Comprising a restoring means for restoring the analog signal forming a digital signal which is output from the riser means interpolating frequencies, the.

According to a second aspect of the audible voice signal high frequency compensating method, an analog signal whose band is limited at a predetermined upper limit frequency is sampled at a sampling frequency which is an integral multiple of 2 or more of the predetermined upper limit frequency. Of the sampling frequency between the digital signal generated in the sampling step and the digital signal generated in the sampling step.
A low-frequency digital signal is obtained by interpolating at an interpolation frequency that is an integer multiple of the above frequency and outputting an interpolated digital signal, and removing the frequency band component above the sampling frequency of the interpolated digital signal generated in the interpolation step. The removal stage that outputs, the equalizer stage that shapes the envelope of the low-frequency digital signal generated in the removal stage into a predetermined envelope and outputs the shaped digital signal, and the shaped digital signal that is generated by the equalizer stage are analogized at the interpolation frequency. A restoration stage for restoring the signal.

[0006]

1 is a block diagram of an embodiment of the present invention, in which an analog audio signal output from an analog sound source (eg, cassette tape recorder) 11 is processed by a processing section 12.
Is input to, and virtual high frequency compensation is performed. The processing unit 12 is mainly composed of a DSP (digital signal processor) 121, a memory 122, an A / D converter 12
3, a D / A converter 124 and a control microcomputer 125.

The processing unit 12 performs high frequency compensation, restores an analog signal, amplifies it by an amplifier 13, and outputs it as sound from a speaker 14. FIG. 2 is a flowchart of a processing routine executed by the processing unit 12, which is executed as an interrupt process at every predetermined timing. FIG. 3 is a frequency spectrum diagram of the processed waveform at each stage, where the horizontal axis represents frequency and the vertical axis represents power.

FIG. 3A is a frequency spectrum diagram of the analog audio signal output from the analog sound source 11.
It is assumed that the upper limit of the frequency band is limited to 8 KHz. In step 21, the analog audio signal is sampled at 16 KHz, which is a frequency double the upper limit frequency of 8 KHz, and is taken into the processing unit 12. 16KH in Fig. 3 (B)
It is a frequency spectrum figure of the analog audio signal of the audio signal after sampling by z, and a folding component is generated in addition to the original frequency band of 8 KHz.

In step 22, so-called zero-order interpolation is performed to add a zero signal to the center of the signal sampled at 16 KHz. Next, in step 23, 16 KHz
High-frequency removal processing with a cut-off frequency of 16 KHz
The above folding components are removed. FIG. 4 is an explanatory diagram of zero-order interpolation, in which the horizontal axis represents time and the vertical axis represents amplitude.

That is, FIG. 4A shows a 16 KHz signal, which exists every 62.5 μsec. FIG. 4B shows the signal after the zero-order interpolation, and the zero signal is inserted between the signals every 62.5 μsec, so that it becomes an apparent sampling signal of 32 KHz. FIG. 4C shows the signal after the high frequency removal processing, and processing for smoothing the waveform in the time domain is performed.

Further, in step 24, an equalizing process for shaping a frequency into a predetermined envelope to obtain a predetermined sound quality is performed, and in step 25, D / A conversion is performed at 32 KHz to obtain a high-frequency-compensated analog audio signal. Output and end this process. It should be noted that in the above embodiment, the analog audio signal is set to the upper limit frequency of 2
Although the A / D conversion is performed at the double frequency, the A / D conversion may be performed at the triple frequency or more.

Although the cutoff frequency of the low-pass filtering process is twice the upper limit frequency, the cutoff frequency can be three times or more. Further, although the interpolation frequency and the D / A conversion frequency are set to four times the upper limit frequency, it is also possible to set the interpolation frequency and the D / A conversion frequency to twice or more the A / D conversion frequency.

[0013]

According to the audible voice signal high-frequency compensating apparatus of the first aspect and the audible voice signal high-frequency compensating method of the second aspect, the virtual signal for the analog signal whose frequency band is limited is virtually calculated. In addition, it becomes possible to compensate for high frequencies above the upper limit frequency.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a flowchart of a processing routine.

FIG. 3 is a frequency spectrum diagram of a processed waveform.

FIG. 4 is an explanatory diagram of zero-order interpolation.

[Explanation of symbols]

 11 ... Analog sound source 12 ... Processing unit 13 ... Amplifier 14 ... Speaker

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Claims (2)

[Claims] 1. Sampling means for sampling an analog signal having a band limited at a predetermined upper limit frequency at a sampling frequency which is a frequency that is an integer multiple of 2 or more of the predetermined upper limit frequency and converting the sampled digital signal into a digital signal. Interpolating means for interpolating the digital signals output from the interpolating digital signal by an interpolating frequency which is a frequency that is an integer multiple of 2 or more of the sampling frequency, and a sampling frequency of the interpolating digital signal output from the interpolating means or more. Removing means for removing the frequency band component of to output a low-frequency digital signal, and equalizer means for shaping the envelope of the low-frequency digital signal output from the removing means into a predetermined envelope and outputting a shaped digital signal, A shaped digital signal output from the equalizer means. The high-frequency compensating apparatus of an audible sound signal comprising a restoring means for restoring into an analog signal, the interpolation frequency. 2. A sampling step of sampling an analog signal of which band is limited at a predetermined upper limit frequency at a sampling frequency which is an integral multiple of 2 or more of the predetermined upper limit frequency and converting the sampled digital signal into a digital signal. An interpolation step of outputting an interpolated digital signal by interpolating between the digital signals generated in 1. with an interpolation frequency that is an integer multiple of 2 or more of the sampling frequency; and a sampling frequency of the interpolated digital signal generated in the interpolation step or more A removing step of removing the frequency band component of the low-frequency digital signal and outputting the low-frequency digital signal, and an equalizer step of shaping the envelope of the low-frequency digital signal generated in the removing step into a predetermined envelope and outputting the shaped digital signal, Interpolate the shaped digital signal generated in the equalizer stage A restoration step for restoring into an analog signal by the wave number, high-frequency compensation method of the audible speech signal consisting of.