Quantize an analog signal

I have an analog signal(ECG) ranging in amplitude from 0.1 to 2.5 and I want to quantize it, to convert the ECG signal into bit stream. The problem I am facing is I don't know what parameters in quantize function will lead to the required quantization range.

Can anyone help me in how to do this using quantize function and what should be the parameters that will lead me to the required range of quantization values.

[Walter Roberson]

Due to the laws of the USA, we are not permitted to discuss encryption.

Answer 1

[Rick Rosson]

Quantize Function

   function y = quantize(x)

      xMin = 0.1;
      xMax = 2.5;

      N = 64;

      y = floor( N * log(x/xMin) / log(xMax/xMin) ) ;

   end

Test Script

   x = 0.1 + 2.4*rand(100,1);
   y = quantize(x);

   scatter(x,y);

HTH.

Rick

[Anas Imtiaz]

This does not work for a sinusoidal function. I don't think this is a valid generic solution.

[Rick Rosson]

It's kind of difficult to provide a general solution when the questioner has not provided all of the necessary information to answer the question. That's why I parameterized my solution, so that it can act as an example of one possible method, and it can be modified depending on the specific requirements.

[Neha Gupta]

i have an Speech signal whose amplitudes are always in the range of -1 and 1. Acoording to your solution my quantized output will always be 0. What changes would you suggest?

[Walter Roberson]

The above code assumes non-negative numbers (notice the log() calls).

Neha Gupta, are you looking for uniform quantization, or non-uniform? If you want non-uniform, then how do you want to determine the widths of the bins ?

[Image Analyst]

Why not use imquantize() from the Image Processing Toolbox where you can specify the edges of the ranges to quantize?

Answer 2

[Rick Rosson]

1. How many quantization levels do you want to have?
2. Do you want uniformly spaced levels, or non?
3. Is the signal signed or unsigned?

[Shravan Kumar Pasupuleti]

I want to have 64 quatization levels.

I want them to be non- uniform as the signal I am dealing is an ECG signal.

I don't know what are signed and unsigned signals?

[Rick Rosson]

Is the value of the signal always greater than zero (one-sided), or is it less than zero some of the time (two-sided)?

Answer 3

[Image Analyst]

If it's already in MATLAB then it's already been quantized. This just changes the quantization to some other quantization. I got the impression he had an analog signal that he needed to quantize (digitize). For that he'd probably need the Data Acquisition Toolbox and an appropriate A-to-D converter device, such as those from Measurement Computing Corporation (like I use) or any of the others listed here. That will take the actual input analog voltage signal and digitize it into a MATLAB variable.