Source Encoding and Decoding

Innovative Technologies in Education (ITE)

The Source encoding and decoding module deals with the theory and applications of signal coding and compression. The experiments provide practical instruction for the more established coding and compression methods such as: PCM, DPCM, ADPCM, DM and ADM.
The encoding unit enables the sampling of the signal in the A/D input, and perform encoding algorithm that would be chosen by DSP (Digital Signal Processing), and transfer it to the output in a form of a Serial Data Stream.

The encoding unit receives the input from the Data and the Clock signals, demodulate them and send them to the output of the A/D.

RECOMMENDED EXPERIMENTS

1. Speech signal characteristics 2. Quantization: uniform, A law, m law 3. Pulse Code Modulation (PCM) 4. Differential Pulse Code Modulation (DPCM) 5. Delta Modulation (DM) 6. Adaptive Differential Pulse Code Modulation (ADPCM) 7. Adaptive Delta Modulation (ADM) 8. Sigma Delta Modulation (SDM) 9. Time Division Multiplexing (TDM)

In the experiments of the above coding methods, the following parameters should be measured and investigated: · sampling rate · compression · quality & intelligibility · mean square error · signal spectrum · quantization noise · distortion

TECHNICAL SPECIFICATIONS

The Source encoding and decoding unit consists of two main operational blocks: The source encoder consists of:

· Dual analog signal multiplexer · 12 bit sampling A/D · DSP implemented quantizer, linear predictor and adaptation · Parallel to serial converter for serial digitized signal (data) transmission · Data and clock out signals

The source decoder consists of:

· Data and clock in signals · Serial to parallel converter · Frame detector (correlator) · DSP implemented code word, adaptation and linear predictor · Dual digital signal demultiplexer · Two channel, 12 bit D/A

DSP (Digital Signal Processing) will be used to monitor and control the various components that will enable communication with the PC, sampling and encoding signals and transmit them in serial form according to the operation that will be defined by the user in the system interface.

APPLICATIONS INTERFACE

A special interface activates a communications Protocol through the RS-232 port for the task defined by the user.

The Applications Interface will consist of the following main features:

· Coder Type-PCM, DPCM, ADPCM, DM, ADM, åDM, · Coder Mode-Single, continuous · Coder Channel-CH1, CH1 & CH2 · Coder Fs (Sampling Frequency)-2KHz, 4KHz, 8KHz, 16KHz, 32KHz · Coder N (Number of Samples)-N=500-60,000, 0-continuous · Function A/D · Function Codec · Function A/D & Codec · Function A/D & Codec · Display Scope · Display Graph

INITIALIZATION PARAMETERS OF THE ENCODER

The following initialization parameters should be defined in the encoder:

-Linear Predictor Factors -Adaptation Factor -Step Size Factor -Quantizer