1. Applications of Multirate Signal Processing
By,
Asha

2. Subband coding of speech signal
Speech signal is represented in the form of digital signal.
It has low frequencies, so lower frequency band encoded with more bits.
Example: Frequency subdivision.

3. Block Diagram of Sub-band Speech Coder

4. Assume speech signal is sampled at a rate Fs samples per second.
The first frequency sub division splits the signal spectrum into equal width segments low pass signals and high pass signals.
The second frequency sub division again splits as above.
Finally third frequency sub division splits the low pass signal from the second stage into two equal band width signals.
Thus the signal is sub divided into 4 frequency bands covering 3 octaves.

5. Decimation by a factor 2 is performed after the frequency sub division.
Therefore we can achieve reduction in the bit rate of the digitalized speech signal.
Filter design is important in sub band coding.
Aliasing can be reduced by using quadrature mirror filters instead of brick wall filters.

6. QMF and Brick wall Filter

7. Synthesis method for the sub band encoded speech signal is basically the reverse of the encoding process.
The signals in adjacent low pass and high pass frequency bands are interpolated, filtered and combined.
A pair QMF is used in the signal synthesis for each octave of the signal

9. Sub band coding is an effective method to achieve data compression in image signal processing.
By combining sub band coding with vector quantization for each sub band signal have obtained coded images with approximately half bit per pixel.
Sub band coding of signal is also used in compression of digital representation of the signal.
Multi-rate signal processing provide efficient implementation of the sub band encoder.