US 5,268,685 AGranted

Apparatus with transient-dependent bit allocation for compressing a digital signal

OwnerYoshihito Fujiwarainventor

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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.

Claims19

Dependent claims

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.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/859,089Filed 27 Mar 1992
Priority: JP 3-09273930 Mar 1991
Granted: 7 Dec 1993
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

H03G 7/007
Volume compression or expansion in amplifiers: of digital or coded signals
G10L 19/032
Using spectral analysis, e.g. transform vocoders or subband vocoders: quantisation or dequantisation of spectral components
G10L 19/002
Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals,…:…
G10L 19/0212
Using spectral analysis, e.g. transform vocoders or subband vocoders: using orthogonal transformation