Adaptive differential pcm

Adaptive differential pcm

1. Adaptive Differential PCM UNIT -2 Presented by Mrs. M.P.Sasirekha

2. In adaptive delta modulation, step size is chosen in accordance with message signal sampled value to overcome slope overload error and hunting. If message is varying at a high rate then step size is high and if message is varying slowly then step size is small. ADPCM has been developed to overcome disadvantages seen by  Delta modulation  system. When signal changes are small, we would like to reduce step size where as to avoid slope overload we would like to increase step size. This is being taken care by ADPCM technique. ADPCM adjusts its step size automatically according to error between m(t) and m^(t).

3. A dvantages of ADPCM: In delta modulation, modulator no longer follow input signal when changes in signal is small and modulator overloads when slope of signal is too high. This problems of DPCM are eliminated or overcome by ADPCM technique. Step size varies according to signal variation. ➨Bandwidth compression is important advantage of ADPCM as only one wire is used for transmission instead of many as in normal digital communication system. Moreover it requires less power to transmit bits. ➨Synchronization problem is also eliminated as here no need of start and stop bits for handshaking. ➨It helps in achieving economic and efficient digital coding of speech with bit rate in the range from 24 Kbps to 32 Kbps. ➨It is simple to implement.

4. D isadvantages of ADPCM In ADPCM, receiver must be able to adapt step sizes in exactly the same manner as the transmitter. ➨Quantization noise is present but no other errors. ➨CVSDM (Continuous Variable Slope Delta Modulation) offers improvement over ADPCM.

5. THANK YOU