Recently developed methods of tree source coding with a fidelity criterion are applied to speech coding. We first demonstrate that tree codes are inherent in A-D speech convertors of the waveform following type and point to ordinary and adaptive delta modulation and differential pulse code modulation (DPCM) as examples. Insights of coding theory improve these trees at low rates; we offer two new code classes, one obtained by smoothing the DPCM tree and one using the rate-distortion theory of autoregressive sources. Using these codes, we study the performance of a simple synchronous tree searching algorithm called the M -algorithm that maintains a small fixed number of paths in contention. 1 and 2 bit/sample code trees, used to encode actual speech at 8, 10, and 16 kbits/s, yield improved dynamic range and channel error resistance, and 4-8 dB improvement in mean-square error (mse) over ordinary single-path searched DPCM. These improvements in excess of analytical estimates suggest that tree coding methods perform better with real-life sources than previously thought.

Tree encoding of speech

This paper presents a new formulation of digital filters that combines the description of signal-processing and arithmetic operations. This is done by noting that multiplication is a form of convolution and therefore normal one-dimensional scalar convolution is in fact two-dimensional binary convolution. This is generalized to multidimensions and can be applied with table-look-up and transform techniques. The result is a unified description that describes a digital filter structure down to the bit level.

Digital filter structures described by distributed arithmetic

Coding schemes for the quantization of line drawings that outperform basic chain codes are investigated. First, subpixel accuracy reconstruction is obtained by a simple linear filtering of the chain code points, which achieves a factor-of-three to-four reduction in average reconstruction distortion for smooth curves. Second, the basic chain encoding schemes are generalized to a multipath-tree-searched encoding scheme. A variation of the (M,L)-algorithm is used to maintain M contending chain code paths in storage and choose the best path from these. Over a wide variety of source curves, tree-searched chain coding results in nearly an order of magnitude reduction in average reconstruction distortion over smoother chain codes. The performance improvement for curves is obtained with only a slight increase in bit rate over basic chain codes. >

Tree searched chain coding for subpixel reconstruction of planar curves

The design of a VLSI chip which applies the ideas of distributed arithmetic to a nonrecursive digital filter is described. The main features of this design are very high precision and a high degree of flexibility, which allows one chip to implement a large number of quite different digital filters and correlators. >

A VLSI implementation of a correlator/digital-filter based on distributed arithmetic

This paper describes an algorithm that is suitable for fast implementations of nonrecursive and recursive digital filters. High speed is realized at the expense of memory; however, the memory-speed tradeoff is flexible so that many hardware and software implementations are practical. When memory is not limited, the time required to compute a filter output value is independent of the order of the filter.

An Algorithm for High-Speed Digital Filters

A method is presented that combines the multiplexing and A/D function to eliminate analog multiplexing switches.

Digital Multiplexing Analog Signals

This paper considers the stability and errors associated with various combinations of hybrid simulation modes, sampling sequences, and compensating schemes.

W.D. Little

Papers

An Algorithm for High-Speed Digital Filters

Digital Multiplexing Analog Signals

Serial Hybrid Computation and Errors in Hybrid Loops