A very small, very flexible, high-quality, linear predictive vocoder has been implemented with commercially available integrated circuit. This fully digital realization is based on a distributed signal processing architecture employing three commercial Signal Processing Interface (SPI) single chip microcomputers. One SPI implements a linear predictive speech analyzer (18), a second implements a pitch analyzer (20), while the third implements the excitation generator and synthesizer (28).

Voice encoder and synthesizer

A very small, flexible, high-quality, full-duplex 2.4-kbit/s linear predictive vocoder has been implemented with commercially available integrated circuits. This fully digital realization is based on a distributed signal processing architecture employing three Nippon Electric Company (NEC) µPD7720 signal processing interface (SPI) single-chip microcomputers. One SPI implements the LPC analyzer, a second implements the Gold pitch and voicing decision algorithm, white the third µPD7720 implements the excitation generator and synthesizer. An Intel 8085-based 8-bit microcomputer is used for data transfer, control and multiplexing functions, and communications with the host terminal. The LPC chip set achieves high flexibility by accepting run time initialization options from the Intel 8085. These parameters include choice of linear predictive model (<= 15), analysis and synthesis frame size, and speech sampling frequency, as well as choice of speech input and output coding formats (linear or µ-255 law) and choice of analog or digjtal pre- and deemphasis. A total of 16 integrated circuits is used in the LPC vocoder with a power disipation of 5.5 W and occupying 18 in/sup 2/ of circuit area.

A Compact, Flexible LPC Vocoder Based on a Commercial Signal Processing Microcomputer

A very small, high-quality, full-duplex 2.4 kbps channel vocoder based on the JSRU Belgard design has been implemented with commercially available integrated circuits. This fully digital realization is based on a distributed signal processing architecture employing six (6) Nippon Electric Company (N.E.C.) µPD7720 Signal Processing Interface (SPI) single chip microcomputers. Three of the µPD7720s implement a Belgard-type analysis filter bank by dividing the 19 channels into groups of 6, 6, and 7 channels. Similarly, a Belgard synthesizer including excitation generation is realized by two SPI's which process and combine the 10- and 9-channel subbands comprising the output speech. A one-chip implementation of the Gold pitch and voicing decision algorithm is achieved with the sixth µPD7720. An intel 8085-based 8-bit microcomputer is used for data transfer, control and multiplexing functions, and communications with the host terminal. Finally, the design features a compact analog subsystem based on a telecommunications industry LSI CODEC-with-filters chip. A total of 26 integrated circuits is required with a power dissipation of 11.5 watts and occupying about 70% of a 7" × 7" wirewrap board (excluding power supply). A very compact, full-duplex 2.4 kbps LPC vocoder has also been designed based on the same architecture as the channel vocoder but requires only three µPD7720s. A total of 16 integrated circuits are used in the LPC vocoder with a power dissipation of 8.6 watts, occupying one-half of a 7" × 7" wirewrap board.

A compact digital channel vocoder using commercial devices

A very small, flexible, high-quality, full-duplex 2.4-kbit/s linear predictive vocoder has been implemented with commercially available integrated circuits. This fully digital realization is based on a distributed signal processing architecture employing three Nippon Electric Company (NEC) μPD7720 signal processing interface (SPI) single-chip microcomputers. One SPI implements the LPC analyzer, a second implements the Gold pitch and voicing decision algorithm, while the third μPD7720 implements the excitation generator and synthesizer. An Intel 8085-based 8-bit microcomputer is used for data transfer, control and multiplexing functions, and communications with the host terminal. The LPC chip set achieves high flexibility by accepting run time initialization options from the Intel 8085. These parameters include choice of linear predictive model ( \leq 15 ), analysis and synthesis frame size, and speech sampling frequency, as well as choice of speech input and output coding formats (linear or μ-255 law) and choice of analog or digital pre- and deemphasis. A total of 16 integrated circuits is used in the LPC vocoder with a power dissipation of 5.5 W and occupying 18 in2of circuit area.

A compact, flexible LPC vocoder based on a commercial signal processing microcomputer

With the availability of single-chip high speed digital signal processors, it is now possible to perform computationally complex voice digitization and compression within single board constraints. A new u-processor based system has been designed, within this constraint, around the TMS-320 signal processor. The hardware blocks needed to accomplish these requirements consists of a high speed microprocessor with fast multiply/accumulate, a data management section, an analog I/O section and a host DMA interface.

A programmable voice digitizer using the T.I. TMS-320 microcomputer

This paper describes a linear predictive coder (LPQ and its microprocessor fabrication. The LPC has an audio bandwidth of 3200 Hz, uses the autocorrelation formulation of LPC to determine the short term spectrum, and an Average Magni- tude Difference Function (AMDF) to extract pitch. A two multiplier/stage lattice filter at the receiver recreates the speech. The 2400 b/s full duplex LPC is implemented in the firmware of a horizontally coded microprocessor having a 48-bit instruction word and 16-bit data word. The processor architecture uses a 4-bit TTL ALU slice and a hardwared 16 x 16 bit parallel multiplier to rapidly process the data with relatively slow multiplication circuitry. With the chosen architecture, the LPC requires only 60 percent of the proces sor's capacity, while the processor itself has fewer than 150 integrated components. The low cost of the voice digitizer has resulted in commercial sales in a market that appears to be growing.

A.J. Goldberg

Papers

Microprocessor Implementation Of A Linear Predictive Coder