Advantages of ADPCM | disadvantages of ADPCM
This page covers advantages and disadvantages of ADPCM. It mentions ADPCM advantages or benefits and ADPCM disadvantages or drawbacks. ADPCM stands for Adaptive differential pulse code modulation.
What is ADPCM?
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.
The short form of Adaptive Delta Pulse Code Modulation is ADPCM. In ADPCM, a difference value that has been mathematically adjusted according to the slope of the input waveform is stored. Bipolar D/A converter is used to convert the stored digital code to analog for playback.
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).
The figure-1 and figure-2 depict ADPCM encoder and ADPCM decoder block diagrams. Beside digital telephone applications, utilization of ADPCM coding is seen in computer storage of digital speech. It is also used in mobile radio telephony, deep space communication and digital encryption.
Benefits or advantages of ADPCM
Following are the benefits or 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.
Drawbacks or disadvantages of ADPCM
Following are the drawbacks or 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.
PCM vs DPCM vs ADPCM
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