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).

6. Advantages 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.

7. Disadvantages 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.

8. THANK YOU