Uniform & Non Uniform Quantization II Encoding II μ-Law and A-Law companding II ADC

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The key difference between uniform and nonuniform quantization is that uniform quantization has equal step sizes while, in nonuniform quantization, the step sizes are not equal. Another important difference between uniform and nonuniform quantization is that, in the uniform quantization, some amount of quantization error can happen, but nonuniform quantization reduces the quantization error.

Uniform Quantization.

Uniform quantization has an equal spacing between the quantization levels. Further, there are two types in uniform quantization. They are mid-tread and mid-rise quantization. Both of these are symmetric about the origin. In the mid-thread quantization, the origin lies in the middle of a tread of the staircase like graph. The quantization levels in mid-thread are odd in number. In the mid-rise quantization, the origin lies in the middle of a rising part of the staircase like graph. The quantization levels in mid-rise are even in number.
• The quantizer in which all the quantile intervals are equal is known as the ‘Uniform Quantization’.
• For a uniform quantizer, the quantization noise is equal for all the levels.
• For speech signals, low volume (Amplitude) signals occur for 50 % of the time. Usually the signal amplitudes are less than 1⁄4 of the RMS value. Only 15% of the time, the signal value exceed the RMS value.
• If the SNR is calculated for uniform quantizer, the SNR for low amplitudes signals is poor as compared to the high amplitude signals. This is because of the uniform distribution of the noise
across all quantization levels.
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Non-Uniform Quantization

In non-uniform quantization, the step size is unequal. After the quantization, the difference between an input value and its quantized value is called the quantization error. As mentioned above, in uniform quantization, the step size is equal. Therefore, some part of the signal might not cover. This can increase quantization error.

However, in case of nonuniform quantization, the step size changes so it will have a minimum amount of error. After completing the quantization, the next step is encoding. It defines each quantization level by a binary code.
• In order to prevent the poor signal to quantization noise ratio, non-uniform
quantization is used.
• In non-uniform quantization, the quantization levels for low amplitude
speech signals are finely distributed which improves the SNR by reducing
the quantization noise
.• One way to perform the non-uniform quantization is by first distorting the input signal with
logarithmic compression and then using the uniform quantization.
• At the receiver, the inverse compression characteristics known as expansion is applied to
recover the signal.
• This compression and expansion characteristics pair is known as ‘Companding’.
• There are two types of companding laws known as ‘μ-Law’ and ‘A-Law’.
Bernard Sklar, Digital Communications- Fundamentals and Applications, 2
nd

Edition.
[2] Louis E. Frenzel Jr., Principles of Electronic Communication Systems, 4
th

Edition McGraw Hill Education, ISBN: 978—0-07-337385-0Bernard Sklar, Digital Communications- Fundamentals and Applications, 2
nd

Edition.
[2] Louis E. Frenzel Jr., Principles of Electronic Communication Systems, 4
th

Edition McGraw Hill Education, ISBN: 978—0-07-337385-0v
[1] B.P. Lathi, Modern Digital and Analog Communication Systems, 3
rd Edition,
[1] Bernard Sklar, Digital Communications- Fundamentals and Applications, 2
nd

Edition.
[2] http://www.soundonsound.com/sos/jan06/articles/qa0106_2.htm
[3] Louis E. Frenzel Jr., Principles of Electronic Communication Systems, 4
th

Edition McGraw Hill Education, ISBN: 978—0-07-337385-0[1] Bernard Sklar, Digital Communications- Fundamentals and Applications, 2
nd

Edition.
[2] http://www.soundonsound.com/sos/jan06/articles/qa0106_2.htm
[3] Louis E. Frenzel Jr., Principles of Electronic Communication Systems, 4
th

Edition McGraw Hill Education, ISBN: 978—0-07-337385-0
Oxford University Press Inc.

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