Data compression system and method for audio signals
First Claim
1. A signal compression system for processing a stream of fixed length digital sample signals comprising,linear digital compression filter means responsive to the stream of digital sample signals for generating a stream of compression-filtered sample signals, the Z-transform of the digital compression filter means having one or more zeros on the unit circle at one or more of the following angular positions;
- 41.41°
, 60°
, 75.52°
, 90°
, 104.48°
, 120°
, 138.59° and
180°
, and not having zeros at any positive angular positions other than 0°
, 41.41°
, 60°
, 75.52°
, 90°
, 104.48°
, 120°
, 138.59° and
180°
.
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0 Petitions
Accused Products
Abstract
Audio signals such as ECG, speech and music are digitally processed to reduce the bit-rate needed for accurate transmission, known as minimizing the entropy of the signal. The transmitter features a digital compression filter with zeros restricted to certain points on the unit circle, and Huffman encoding for transmission. The receiver features a digital decompression filter with poles at the zero locations, but shifted inside the unit circle to prevent error-ramp build-up.
85 Citations
23 Claims
-
1. A signal compression system for processing a stream of fixed length digital sample signals comprising,
linear digital compression filter means responsive to the stream of digital sample signals for generating a stream of compression-filtered sample signals, the Z-transform of the digital compression filter means having one or more zeros on the unit circle at one or more of the following angular positions; - 41.41°
, 60°
, 75.52°
, 90°
, 104.48°
, 120°
, 138.59° and
180°
, and not having zeros at any positive angular positions other than 0°
, 41.41°
, 60°
, 75.52°
, 90°
, 104.48°
, 120°
, 138.59° and
180°
. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
- 41.41°
-
15. A system for compressing audio data in the form of a stream of fixed length digital sample signals comprising,
means for forming the stream of sample signals into equal length data blocks, adaptive digital compression filter means responsive to the blocks of sample signals for generating a stream of compression-filtered sample signals, the transfer function of said compression filter means having zeros on the unit circle in the Z-plane, digital encoding means responsive to the stream of compression-filtered sample signals from the digital compression filter means and implementing a variable word length code, the output from the digital encoding means comprising blocks of encoded compression-filtered sample signals, means for adjusting the angular positions of the zeros of the transfer function in the Z-plane of the digital compression filter means for each block of sample signals supplied thereto to substantially minimize the entropy of the blocks of encoded compressed sample signals from said digital encoding means, the positive angular positions to which said zeros may be adjusted by said adjusting means being restricted to 0° - , 41.41°
, 60°
, 75.52°
, 90°
, 108°
48°
, 120°
, 138.59° and
180°
, andmeans for inserting an identifying code word with each block of encoded compressed sample signals from the digital encoding means for identifying the angular positions of the zeros of the transfer function of the digital compression filter means employed to substantially minimize the entropy of the blocks of encoded compression-filtered sample signals. - View Dependent Claims (16)
- , 41.41°
-
17. In a method of filtering a stream of fixed length digital sample signals, the steps comprising,
supplying the stream of sample signals to a linear digital compression filter means, operating the digital compression filter means with a transfer function in the Z-plane having one or more zeros on the unit circle at one or more of the following angular positions as measured form the origin as follows: - 41.41°
, 60°
, 75.52°
, 90°
, 104.48°
, 120°
, 138.59°
, and 180°
,restricting operation of the digital compression filter means so that it does not operate with zeros at any positive angular position other than at 0°
, 41.41°
, 60°
, 75.52°
, 90°
, 104.48°
, 120°
, 138.59° and
180°
. - View Dependent Claims (18, 19, 20, 21, 22)
- 41.41°
-
23. In a method of filtering audio data which is in the form of a stream of fixed length digital sample signals, the steps comprising
compression filtering successive blocks of sample signals by adaptive compression filter means having zeros on the unit circle in the Z-plane, encoding the successive blocks of compression filter sample signals from the compression filter means using an encoder which implements a variable word length code, controlling the angular positions of the zeros of the transfer function in the Z-plane of the compression filter means to substantially minimize the entropy of the successive blocks of signals from the encoder, restricting operation of the compression filter means to provide for zeros in the Z-plane transfer function thereof at only one or more of the angular positions of 0° - , ±
41.41°
, ±
60°
, ±
75.52°
, ±
90°
, ±
108.48°
, ±
120°
, ±
138.59°
, and 180°
.
- , ±
Specification