Apparatus with transient-dependent bit allocation for compressing a digital signal
First Claim
1. An apparatus for compressing a digital input signal, the apparatus comprising:
- frequency dividing means for dividing the digital input signal into signal into signal components in plural frequency ranges;
time dividing means for dividing the components in time into a signal component in blocks in each frequency range;
orthogonal transform processing means for orthogonally transforming the signal components in blocks;
bit allocating means for allocating quantizing bit numbers to the orthogonally-transformed signal components in blocks, thereby to quantize them;
transient state determining means for determining a transient state of a time domain signal before the orthogonal transform processing means; and
bit number altering means for altering the bit numbers allocated to the orthogonally-transformed signal components in blocks in response to the transient state determined by the transient state determining means.
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Abstract
A digital input signal is divided into signal components in plural frequency ranges by band division filters. The signal components thus obtained are divided in time into signal components in blocks in the respective frequency bands, and are also sent to a transient detector, which determines a transient state for each blocks. Changing an allowed noise level calculating circuit in response to the determined transient states, or any similar method, alters the quantizing bit numbers allocated to each block by an adaptive bit allocation circuit. The allocated bit numbers are altered depending upon the transient state of each block to improve the signal-to-noise ratio in blocks including a transient. Quantizing noise pre echo occurring before the transient, a phenomenon that is offensive to the ear, is prevented.
75 Citations
19 Claims
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1. An apparatus for compressing a digital input signal, the apparatus comprising:
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frequency dividing means for dividing the digital input signal into signal into signal components in plural frequency ranges; time dividing means for dividing the components in time into a signal component in blocks in each frequency range; orthogonal transform processing means for orthogonally transforming the signal components in blocks; bit allocating means for allocating quantizing bit numbers to the orthogonally-transformed signal components in blocks, thereby to quantize them; transient state determining means for determining a transient state of a time domain signal before the orthogonal transform processing means; and bit number altering means for altering the bit numbers allocated to the orthogonally-transformed signal components in blocks in response to the transient state determined by the transient state determining means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification