Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-09-17
2003-07-01
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C341S155000, C341S051000
Reexamination Certificate
active
06587984
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a distortion detecting device, a distortion correcting device, and a distortion correcting method for detecting the generated distortion accompanying the linearity error (conversion error) of an analog/digital converter when an analog audio signal is converted to a digital audio signal through analog-digital conversion by the analog/digital converter.
BACKGROUND ART
Heretofore, analog/digital converters (A/D converters) contained linearity error in accordance with the A/D conversion precision. When the A/D converter converts an analog signal to a digital signal, distortion is generated accompanying the linearity error (hereinafter referred to as “conversion error”) of the A/D converter in the converted digital audio signal. In this case, when performing A/D conversion with the A/D converter, it is possible to reduce to a certain degree the distortion based on the conversion error at the time of A/D conversion by adjusting the internal resistance of the A/D converter or adjusting the bit weighting with an external circuit.
However, a great number of music software titles, which were digitally recorded in the past using A/D conversion (digital audio signals recorded in the past), were converted from analog to digital by A/D converters having poor conversion precision at a low number of bits (such as 13 bits or 14 bits). Consequently, the A/D converters themselves contained conversion errors even if adjusted (and contained considerable distortion based on the conversion error compared to modern (such as 16-bit) A/D converters) and the distortion accompanying the conversion error due to poor conversion precision becomes one cause of degraded quality of the recorded music signal. Therefore, it is presently preferable to obtain digital audio signals having reduced distortion based on the conversion error of the A/D converters that were used in the past at the time of the recording.
In this case, it is possible to measure the characteristics of the A/D converters that were used in the past at the time of the recording and to correct the A/D conversion error based on these characteristics. However, since the characteristics of A/D converters deteriorate with time, the characteristics at the time of A/D conversion, namely, the conversion error, cannot be detected accurately from the A/D converters that were used at the time of the A/D conversion. Furthermore, 13-bit or 14-bit A/D converters that were used at the time of recording generally do not presently exist. In this case, the characteristics of the A/D converters cannot be detected from the A/D converters. It is thus difficult to accurately detect the A/D conversion error of the digital audio signals regardless of whether or not the 13-bit or 14-bit A/D converters that were used in the past at the time of the recording are currently available, and resulted in a problem where the A/D conversion error could not be reduced.
It was also difficult to estimate (detect) the conversion error at the time of A/D conversion from the digital audio signal that was recorded with distortion based on the conversion error (pre-recorded music signal). A known measurement device using a sine wave histogram method estimates (detects) the conversion error of the A/D conversion from the digital audio signal. After a distortion-free sine wave is fed to an A/D converter to be measured, a histogram is obtained and the measurement device uses the histogram to measure the conversion error that is to be measured. However, if the signal source, such as a digital audio signal, is not a sine wave, the conversion error could not be estimated (detected).
In this manner, it was difficult hitherto to estimate (detect) the conversion error at the time A/D conversion from the digital audio signal (music signal), which was already recorded using A/D conversion, and therefore, a digital audio signal with reduced distortion based on the conversion error at the time of A/D conversion could not be obtained.
It is therefore an object of the present invention to provide a distortion detecting device, a distortion correcting device, and a distortion correcting method for making it possible to correct the digital audio signal so as to reduce the distortion included in the digital audio signal by estimating (detecting) the distortion based on the linearity error of the A/D converter at the time of A/D conversion from the digital audio signal (pre-recorded music signal) that was converted from analog to digital by the A/D converter having linearity error.
DISCLOSURE OF THE INVENTION
The distortion detecting device for digital audio signal relating to the present invention comprises storage means for storing a digital audio signal, occurrence frequency detecting means for extracting a plurality of samples from the digital audio signal stored in the storage means and counting the occurrence frequency of the sample for every code expressing a quantization level of the sample, normalizing means for extracting a distortion characteristic accompanying the linearity error of an analog/digital converter as a normalized occurrence frequency from the occurrence frequency for every code detected by the occurrence frequency detecting means, and error bit detecting means for detecting an error bit from a difference between codes of the normalized occurrence frequency extracted by the normalizing means.
According to the present invention, even though the analog/digital converter that generated the digital audio signal including conversion error does not exist, the distortion based on the linearity error of the analog/digital converter can be detected on the basis of the generated digital audio signal.
The distortion correcting device for digital audio signal relating to the present invention comprises conversion error detecting means for detecting the error bit influenced by the linearity error of the analog/digital converter from the occurrence frequency for every code of the digital audio signal converted to code by the analog/digital converter, and conversion error correcting means for correcting the error bit of the digital audio signal based on a detection result from the conversion error detecting means.
According to the present invention, the bit at which the distortion accompanying the linearity error of the analog/digital converter is generated is detected, and based on this detection result, the bit concerning the distortion is corrected so that the distortion of the digital audio signal generated including conversion error can be reduced.
In the distortion correcting device for digital audio signal relating to the present invention, the conversion error detecting means comprise the storage means for storing the digital audio signal, the occurrence frequency detecting means for extracting a plurality of samples from the digital audio signal stored in the storage means and counting the occurrence frequency of the sample for every code expressing a quantization level of the sample, the normalizing means for extracting the distortion characteristic accompanying the linearity error of the analog/digital converter as normalized occurrence frequency from the occurrence frequency for every code detected by the occurrence frequency detecting means, and the error bit detecting means for detecting the error bit based on the code corresponding to a feature of the normalized occurrence frequency.
According to the present invention, the normalization of the occurrence frequency causes the feature dependent on the digital audio signal for which samples were collected to be removed and the conversion characteristic of the analog/digital converter at the time of generating the digital audio signal to be extracted. Thus, the distortion correcting device according to the present invention can correct an arbitrary digital audio signal generated with the same conversion characteristic as the analog/digital converter.
In the distortion correcting device for digital audio signal relating to the present invention, the occurrence frequency detecting means
De'cady Albert
Dickstein , Shapiro, Morin & Oshinsky, LLP
Lamarre Guy
Nippon Columbia Co. Ltd.
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