Band correcting apparatus

• US 7,805,293 B2
• Filed: 02/26/2004
• Issued: 09/28/2010
• Est. Priority Date: 02/27/2003
• Status: Active Grant

• Current Assignee: OKI Electric Industry Company Limited
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Murakami, Yoshinari, Takada, Masashi
• Primary Examiner(s): Hudspeth; David R
• Assistant Examiner(s): Guerra-Erazo; Edgar
• Application Number:
  US10/545,670
• Publication Number:
  US 20060142999A1
• Time in Patent Office: 2,406 Days
• Field of Search: 704/200.1, 704/500, 704/501, 704/502, 704/503, 704/504, 704205-210, 704/203, 704/225, 330/278
• US Class Current: 704/205
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

A voice band correcting apparatus in which the signal level of limit bands is amplified by a correction filter, the signal level of a correction signal supplied is compared by a level detector to a preset level, and the result of decision is sent as level information to a coefficient controller, where the signal level is adjusted in a controlled manner. The high-quality broadband signal may be obtained on correction without degrading the quality of a communication signal ascribable to excess amplification.

Claims

1. A band correcting apparatus, comprising:

a corrector receiving an input signal that is limited in a frequency band for correcting the input signal with a gain to output a corrected signal, the gain being lower in a limited band and higher outside the limited band;

a monitor for monitoring whether or not a signal level of the corrected signal falls between preset maximum and minimum values to output level information; and

a level adjustor for adjusting a signal level of the input signal responsive to the level information from said monitor,

wherein said level adjustor includes a coefficient controller responsive to the level information for controlling a coefficient defining the gain, and

wherein said corrector comprises a first filter for amplifying a band signal, excluding the input signal that is limited in a frequency band, and a second filter for applying a delay to a signal of the band excluding the limit band of the band-limited input signal, the delay being substantially equivalent to a delay of the band-limited input signal;

wherein said monitor and said level adjustor are provided correspondingly in number to the band signal of the first filter;

wherein said level adjustor includes a coefficient controller and a multiplier for multiplying the coefficient from said coefficient controller with the input signal; and

wherein said apparatus further comprising an adder for summing an output of said first and second filter.

2. The apparatus in accordance with claim 1, wherein said level adjustor comprises:

a level amplifier for controlling a coefficient for amplifying the input level; and

a coefficient controller for outputting the coefficient for amplifying the level of the input signal depending on the level information.

3. A band correcting apparatus comprising:

a band splitter for splitting a band of an input signal into a plurality of limit bands; and

a corrector for correcting a signal level of the bands obtained by splitting for outputting correction signals

wherein said band splitter comprises;

a first delay circuit for applying a delay to a signal other than the limit band of the band-limited input signal, the delay being substantially equivalent to a delay attendant on filtering of the band-limited input signal; and

a second delay circuit for applying a delay substantially equivalent to a delay attendant on processing by said corrector, and

wherein said apparatus further comprises;

a monitor for monitoring whether or not a signal level of a corrected signal falls between preset maximum and minimum values to output level information; and

a level adjustor for adjusting a signal level of the band-limited input signal responsive to the level information from said monitor,

wherein said corrector receives the band-limited input signals for correcting the band-limited input signal with a gain to output the corrected signal, the gain being lower in a limited band and higher at least outside the limited band, and

wherein said level adjustor outputs a plurality of coefficients responsive to the level information for controlling the plurality of coefficients defining the gain to said corrector.

4. The apparatus in accordance with claim 3, wherein said corrector comprises:

a first filter for amplifying a band signal output from said first delay circuit; and

a second filter for amplifying a band signal output from said second delay circuit.

5. The apparatus in accordance with claim 3, wherein said apparatus conforms to the standard of the ITU-T (International Telecommunication Union Telecommunication standardization sector) recommendations G.722.

6. The apparatus in accordance with claim 5, wherein said band splitter comprises a quadrature mirror filter for conforming to said standard and splitting the band of the input signal into a low sub-band and a high sub-band;

said corrector including;

a low-range corrector for correcting a level of the low sub-band; and

a high-range corrector for correcting a level of the high sub-band;

said apparatus further comprising a shifter for shifting a frequency of an output signal of the high sub-band output by said analog converter.

7. The apparatus in accordance with claim 6, further comprising a third filter provided downstream of said low-range corrector for splitting the band.

8. The apparatus in accordance with claim 7, wherein said third filter includes a quadrature mirror filter.

9. The apparatus in accordance with claim 6, further comprising a phase adjustor for adjusting a phase or a delay of an output signal from said low-range corrector.

10. The apparatus in accordance with claim 7, further comprising a phase adjustor for adjusting a phase or a delay of an output signal from said third filter.

11. A band correction apparatus, comprising:

means for filtering an audio-frequency input signal having a low frequency component below an intermediate frequency band, an intermediate frequency component in the intermediate frequency band, and a high frequency component above the intermediate frequency band;

means for determining whether either the filtered high frequency component of the input signal or the filtered low frequency component of the input signal exceeds a predetermined signal level;

means for attenuating the high frequency component of the input signal before it is filtered if the filtered high frequency component of the input signal exceeds the predetermined signal level, and for attenuating the low frequency component of the input signal before it is filtered if the filtered high frequency component of the input signal exceeds the predetermined signal level; and

means for combining the filtered low frequency, intermediate frequency, and high frequency components of the input signal so as to provide a corrected output signal.

12. The apparatus of claim 11, wherein the intermediate frequency bank ranges from about 300 Hz to about 3.4 kHz.

13. The apparatus of claim 11, wherein the means for filtering comprises first means for filtering the low frequency component of the input signal, second means for filtering the intermediate frequency component of the input signal, and third means for filtering the high frequency component of the input signal.

14. The apparatus of claim 11, wherein the means for combining comprises an adder.