Device for recovering missing frequency components

• US 20070168185A1
• Filed: 02/10/2004
• Published: 07/19/2007
• Est. Priority Date: 02/14/2003
• Status: Active Grant

• Current Assignee: OKI Electric Industry Company Limited
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Takada, Masashi
• Granted Patent: US 7,539,613 B2
• Time in Patent Office: Days
• US Class Current: 704/205
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A band recovering device recovers frequency components lying in a frequency band lost due to band-limitation of a sound signal. The device includes a peak-limiting amplifier for amplifying an input narrow-band signal while preventing the resulting amplified signal from exceeding a maximum amplitude. A peak-limitation detector detects the level of the amplified signal output. An amplification controller increases the amplification factor and/or the amount of amplification of the peak-limiting amplifier in accordance with the level of the amplified signal. A band recovering circuit generates, based on the amplified signal output from the peak-limiting amplifier and input narrow-band signal, a band-recovered signal including the frequency components lying in the missing band.

Claims

1. A band recovering device for recovering frequency components lying in a frequency band lost due to band-limitation of a sound signal, comprising:

a peak-limiting amplifier configured to amplify an input narrow-band signal while preventing a resulting amplified signal from exceeding a maximum amplitude;

a peak-limitation detector configured to detect a level of the amplified signal output from said peak-limiting amplifier;

an amplification controller configured to increase at least either one of an amplification factor and an amount of amplification of said peak-limiting amplifier in accordance with the level of the amplified signal output from said peak-limitation detector; and

a band recovering circuit configured to generate, based on the amplified signal output from said peak-limiting amplifier and the input narrow-band signal, a band-recovered signal including the frequency components lying in the frequency band lost.

2. The device in accordance with claim 1, further comprising a voice detector configured to detect at least a voiced sound signal on the basis of the input narrow-band signal,

wherein said amplification controller increases at least either one of the amplification factor and the amount of amplification when said voice detector is detecting at least a voiced sound signal.

3. The device in accordance with claim 2, further comprising a frequency shifter configured to shift frequency components of the input narrow-band signal toward the frequency band to be recovered,

wherein said voice detector detects at least an unvoiced sound signal on the basis of the input narrow-band signal, and

wherein said frequency shifter shifts the frequency components of the input narrow-band signal toward the frequency band to be recovered only when said voice detector is detecting an unvoiced sound signal.

4. The device in accordance with claim 1, further comprising a frequency shifter configured to shift frequency components of the input narrow-band signal toward the frequency band to be recovered, and a voice detector configured to detect at least an unvoiced sound signal on the basis of the input narrow-band signal;

wherein said frequency shifter shifts the frequency components of the input narrow-band signal toward the frequency band to be recovered when said voice detector is detecting an unvoiced sound signal.

5. The device in accordance with claim 1, wherein said band recovering circuit comprises an amplitude adjusting section configured to adjust an amplitude of the amplified signal output from said peak-limiting amplifier for outputting an adjusted signal, and a signal generating section configured to combine said adjusted signal with the input narrow-band signal in a preselected ratio for thereby generating the band-recovered signal.

6. The device in accordance with claim 5, wherein said amplitude adjusting section comprises a band-pass filter configured to pass only frequency components of a frequency band necessary for recovery.

7. The device in accordance with claim 5, wherein said amplitude adjusting section comprises a characteristic correcting filter configured to pass frequency components of a frequency band necessary for recovery while adjusting amplitudes of said frequency components in accordance with said frequency band.

8. A telephone set comprising a band recovering device for recovering frequency components lying in a frequency band lost due to band-limitation of a sound signal, wherein said band recovering device comprises:

a peak-limiting amplifier configured to amplify an input narrow-band signal while preventing a resulting amplified signal from exceeding a maximum amplitude;

a peak-limitation detector configured to detect a level of the amplified signal output from said peak-limiting amplifier;

an amplification controller configured to increase at least either one of an amplification factor and an amount of amplification of said peak-limiting amplifier in accordance with the level of the amplified signal output from said peak-limitation detector; and

a band recovering circuit configured to generate, based on the amplified signal output from said peak-limiting amplifier and the input narrow-band signal, a band-recovered signal including the frequency components lying in the frequency band lost.

9. A band recovering device for recovering frequency components lying in a frequency band lost due to band-limitation of a sound signal, comprising:

an amplitude limiter configured to limit an upper limit of a signal value of the input narrow-band signal;

a detector configured to detect a level of the signal value of the input narrow-band signal;

an amplitude-limit controller configured to decrease the upper limit in accordance with an output of said detector; and

a band recovering circuit configured to generate, based on a signal output from said amplitude limiter and the input narrow-band signal, a band-recovered signal including the frequency components lying in the frequency band lost.

10. The device in accordance with claim 9, further comprising a voice detector configured to detect at least a voiced sound signal on the basis of the input narrow-band signal,

wherein said amplitude-limit controller reduces the upper limit when said voice detector is detecting at least a voiced sound signal.

11. The device in accordance with claim 10, further comprising a frequency shifter configured to shift frequency components of the input narrow-band signal toward the frequency band to be recovered,

wherein said voice detector detects at least an unvoiced sound signal on the basis of the input narrow-band signal, and

wherein said frequency shifter shifts the frequency components of the input narrow-band signal toward the frequency band to be recovered only when said voice detector is detecting an unvoiced sound signal.

12. The device in accordance with claim 9, further comprising a frequency shifter configured to shift frequency components of the input narrow-band signal toward the frequency band to be recovered, and a voice detector configured to detect at least an unvoiced sound signal on the basis of the input narrow-band signal;

wherein said frequency shifter shifts the frequency components of the input narrow-band signal toward the frequency band to be recovered when said voice detector is detecting an unvoiced sound signal.

13. The device in accordance with claim 9, wherein said band recovering circuit comprises an amplitude adjusting section configured to adjust an amplitude of a signal output from said amplitude limiter for thereby outputting an adjusted signal, and a signal generating section configured to combine said adjusted signal with the input narrow-band signal in a preselected ratio for thereby generating the band-recovered signal.

14. The device in accordance with claim 13, wherein said amplitude adjusting section comprises a band-pass filter configured to pass only frequency components of a frequency band necessary for recovery.

15. The device in accordance with claim 13, wherein said amplitude adjusting section comprises a characteristic correcting filter configured to pass frequency components of a frequency band necessary for recovery while adjusting amplitudes of said frequency components in accordance with said frequency band.

16. A telephone set comprising a band recovering device for recovering frequency components lying in a frequency band lost due to band-limitation of a sound signal, wherein a band recovering device comprises:

an amplitude limiter configured to limit an upper limit of a signal value of the input narrow-band signal;

a detector configured to detect a level of the signal value of the input narrow-band signal;

an amplitude-limit controller configured to decrease the upper limit in accordance with an output of said detector; and

a band recovering circuit configured to generate, based on a signal output from said amplitude limiter and the input narrow-band signal, a band-recovered signal including the frequency components lying in the frequency band lost.