Excavating
Patent
1996-09-23
1998-06-02
Baker, Stephen M.
Excavating
371 31, 375254, G11B 2018, G11B 2024, H04B 1404, H04B 1500
Patent
active
057612188
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of and apparatus for interpolating a digital signal, and more particularly to a method of and apparatus for interpolating a digital signal which has been digitized with a small number of bits.
BACKGROUND ART
Recording/playback mediums such as CDs (Compact Discs), DATs (Digital Audio Tapes), etc. and digital audio broadcasting services such as satellite broadcasting services have heretofore been put to use as means for digitizing and transmitting audio signals (the term "transmission" used herein includes recording and reproduction of signals). In such a digital audio transmission apparatus, it has been customary to convert an analog signal into a digital signal according to a prescribed format including a sampling frequency of 48 kHz, 44.1 kHz, or the like and a number of quantizing bits such as 16 bits.
In the conventional digital audio transmission apparatus, the number of quantizing bits for digital audio signals generally governs the dynamic range of audio signals to be demodulated. For transmitting audio signals of higher sound quality, therefore, it is necessary to expand the number of quantizing bits from the current standard of 16 bits to 20 or 24 bits. Once a format for signal transmission is determined, however, since the number of quantizing bits cannot easily be expanded, it is not possible to produce audio signals of higher sound quality from the digital audio transmission apparatus.
One process known as .SIGMA..DELTA. (sigma-delta) modulation for digitizing audio signals has been proposed (see "AD/DA converter and digital filter" by Yoshio Yamazaki, Japan Acoustic Society Journal Vol. 46, No. 3 (1990), pages 251-257).
FIG. 1 of the accompanying drawings shows an arrangement for 1-bit .SIGMA..DELTA. modulation. As shown in FIG. 1, an audio signal inputted from an input terminal 91 is supplied through an adder 92 to an integrator 93, which supplies; an output signal to a comparator 94. The comparator 94 compares the output signal from the integrator 93 with a midpoint potential of the inputted audio signal, and quantizes the output signal from the integrator 93 into a 1-bit quantized signal in each of sampling periods. The frequency of the sampling periods (sampling frequency) is 64 or 128 times the conventional sampling frequency of 48 kHz or 44.1 kHz.
The quantized signal is supplied to a delay unit 95, which delays the quantized signal by one sampling period. The delayed signal is then supplied through a 1-bit D/A converter 96 to the adder 92, which adds the delayed signal to the audio signal inputted from the input terminal 92. The quantized signal from the comparator 94 is also delivered to an output terminal 97. According to the above .SIGMA..DELTA. modulation, as also indicated by the literature referred to above, it is possible to obtain a digital audio signal having a wide dynamic range even with a few number of 1 bits by sufficiently increasing the frequency of sampling periods (sampling frequency).
If the transmission system for transmitting the above digital audio signal suffers a failure, resulting in a signal loss, the reproduced digital signal is fixed to a value of either "1" or "0". For the digital audio signal which is not processed, e.g., which is produced by the arrangement shown in FIG. 1, the successive values of "1" and "0" correspond respectively to a positive maximum value and a negative maximum value of the demodulated signal. Therefore, in the event that part of the signal is lost while in the transmission system, maximum-level noise is produced at the lost part of the signal, tending to break a monitor amplifier or speaker.
Accordingly in CDs, DATs, etc., a signal format is determined such that the successive values of "1" and "0" will become an intermediate value of the demodulated signal. Therefore, no maximum-level noise is produced even when the above signal loss occurs. An error-correcting code is included in a digital signal which is transmitted, thereby recovering the signal in a certain range even
REFERENCES:
patent: 4451921 (1984-05-01), Odaka
patent: 5586192 (1996-12-01), De Bijl et al.
Baker Stephen M.
Maioli Jay H.
Sony Corporation
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