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What is the need of multirate processing? Give some examples of multirate digital systems.
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Solution:

A multirate system can increase or decrease the sampling rate of individual signals.

These signals can be simultaneously processed in various components of the multirate systems.

Hence the sampling rate of the signal must be altered as it propagates from one component to another.

The signal processing that uses more than one sampling rate to perform the desired operations is known as multirate signal.

There are two approaches to altering the sampling rate of a digital signal.

(1) $D / A$ to $A / D$ conversion.

(2) Digital Domain.

In multirate system, we change the sampling rate of a signal digitally using downsamples and upsamplers.

Downsampling decreases the sampling rate \& it is usually preceded by a low pass \Upsampling increases the sampling rate of the signal s it is usually followed by $L P F$.

High-quality data acquisition and storage systems are increasingly taking advantage of multirate techniques to avoid the use of expensive anti-aliasing analog filters and to handle efficiently signals of different bandwidths which require different sampling frequencies.

A good example of such a system is the ED 8000 (Earth Data UK) Tape recorder.

In speech processing, multi rate techniques are employed to reduce the storage space or the transmission rate of speech data.

Estimates of speech parameters are computed at a very low sampling rate for storage or transmission.

When required, the original speech is reconstructed from the low bit rate representation at much higher rates using the multirate approach.

Multirate processing has found important application in the efficient implementation of Dip functions.

For example, the implementation of a narrowband digital FIR filter using conventional DSP poses a serious problem because such filters require a very large number of coefficients to meet their tight frequency response specifications.

The use of multirater techniques leads to very efficient implementation by allowing filtering to be performed at a much lower rate, which greatly reduces the filter order.

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