Distortion detecting device, distortion correcting device, and distortion correcting method for digital audio signal

• US 6,587,984 B1
• Filed: 09/17/1999
• Issued: 07/01/2003
• Est. Priority Date: 03/18/1997
• Status: Expired due to Fees

• Current Assignee: Nippon Columbia Co., Ltd. (Faith, Inc.)
• Original Assignee: Nippon Columbia Co., Ltd. (Faith, Inc.)
• Inventors: Tsukamoto, Masaki
• Primary Examiner(s): Decady, Albert
• Assistant Examiner(s): LAMARRE, GUY J
• Application Number:
  US09/381,202
• Time in Patent Office: 1,383 Days
• Field of Search: 360/48, 360/72.2, 360/137, 360/69, 360/71, 360/32, 360/8, 341/144, 341/56, 341/69, 341/155, 341/50, 341/51, 341/131, 369/30, 369/18, 710/240, 700/94, 704/205, 704/211, 704/270, 714/752, 714/746, 375/216, 375/316, 375/344, 375/286, 386/2, 386/20, 386/104, 386/100, 386/96, 348/497, 455/182, 455/2
• US Class Current: 714/746
• CPC Class Codes: H03M 1/1038 by storing corrected or correction values in one or more digital look-up tables H03M1/1057 takes precedence
• CPC Class Codes: H03M 1/12 Analogue/digital converters H03M1/001 – H03M1/10 take precedence

Abstract

A digital audio signal distortion detecting device is provided for estimating the distortion based on the linearity error of an analog/digital converter at the time of analog/digital conversion from a digital audio signal converted from analog to digital by the analog/digital conversion having linearity error. This device includes storage means (2) for storing the digital audio signal, occurrence frequency detecting means (3) for fetching a plurality of samples from the digital audio signal stored in the storage means (2) and counting the occurrence frequency of the samples for every code expressing the quantization level of the samples, normalizing means (4) for extracting distortion characteristics accompanying the linearity error of an A/D converter (11) from the occurrence frequency for every code detected by the occurrence frequency detecting means (3) as a normalized occurrence frequency, and error bit detecting means (5) for detecting an error bit on the basis of the code corresponding to the characteristics of the normalized occurrence frequency.

Claims

1. A digital audio signal distortion correcting device comprising:

storage means (2) for storing a digital audio signal converted to code by an analog/digital converter;

occurrence frequency detecting means (3) for extracting a plurality of samples from said digital audio signal stored in said storage means (2) and counting an occurrence frequency of said samples for every code expressing a quantization level of the samples to obtain a level distribution;

normalizing means (34) for generating, by applying a low-pass filtering process on the original level distribution detected by said occurrence frequency detecting means (3), an ideal level distribution approximating an ideal case where said analog/digital converter has no error, dividing said original level distribution by said ideal level distribution, and setting the division result thereof as a normalized level distribution;

conversion table calculating means (35) for calculating, based on said normalized level distribution, a conversion table in which data bit lengths are extended to make a correction with respect to a conversion error of said analog/digital converter for all of said quantization levels of said digital audio signal; and

data substituting means (36) for substituting said quantization level of said digital audio signal with level data according to said conversion table for output.

2. A digital audio signal distortion correcting method comprising the steps of:

estimating a conversion error for an analog/digital converter that is used, from a level distribution of a digital audio signal recorded using the analog/digital converter;

calculating, based on the estimated conversion error, a conversion table in which data bit lengths are extended to make a correction with respect to the conversion error of said analog/digital converter for all quantization levels of said digital audio signal; and

performing a conversion process using said conversion table on said digital audio signal to correct a distortion generated by the conversion error of said analog/digital converter while extending bits.

3. A distortion correcting method comprising the steps of:

collecting a predetermined number of samples from a digital audio signal recorded using an analog/digital converter to obtain a level distribution of the concerned samples;

applying a low-pass filtering process on said level distribution to generate an ideal level distribution approximating an ideal case where the analog/digital converter has no error;

dividing said level distribution, before said low-pass filtering process was applied, by said level distribution, and accumulating the divided result to set the divided result thereof as a normalized level distribution,

carrying out accumulation based on the normalized level distribution to calculate a conversion table in which data bit lengths are extended to make a correction with respect to a conversion error of said analog/digital converter for all quantization levels of said digital audio signal; and

substituting the quantization level of the digital audio signal with the level data according to the conversion table for output.