Quantizing a audiorecorder sample in MATLAB

Question

I have a recorded a sound wave (16-bit single channel) using audiorecorder and I need to quantize it into 15 bits (removing LSB) without using toolboxes other than MATLAB built-in ones. Can anyone help on this?

fs = 8000;
tmax = 2;
nbits = 16;
nchan = 1;
Recorder = audiorecorder(fs, nbits, nchan);
record(Recorder);
pause(tmax);
stop(Recorder);

More details please. Any example code? How many bits are you starting with and how many do you want to quantize to? — crowdedComputeeer, Aug 18 '15 at 03:32
Still confused, you're starting with 16 bits and you want to quantize to 16 bits? What am I missing? — crowdedComputeeer, Aug 18 '15 at 03:55
@crowdedComputeeer yes it is but I am not asking for the solution. I am only asking for the method here. That's why the original post was too brief. — Bababarghi, Aug 18 '15 at 04:04

score 0 · Answer 1 · answered Aug 18 '15 at 04:29

Ok, since you acknowledge this is a homework question and are asking for a method not a solution, first, you need the signal values

x = Recorder.getaudiodata('int16');

Since you are going to be quantizing you might as well start with values in the right range, as opposed to doubles which would be normalized [-1, 1]

So, next you need to quantize from 16 bits to 15. This is actually pretty easy in matlab, if you're writing a ton of code, it's probably not working. There are several ways you could do it.

Essentially, you're throwing away half the information when you remove 1 bit.

Take the numbers 0, 1, 2, 3 which have 2 bit precision. In binary, 00, 01, 10, 11. If I quantize to one bit, I throw away half the information. Imagine the LSB is gone, I'd have 0, 0, 1, 1. But, my original numbers span 0 to 3... Typically you want your numbers to have the same dynamic range. So, I threw half the numbers away, what if I scale the new numbers by 2? I get 0, 0, 2, 2. This is a correct quantization from 2 to 1 bit.

In your problem, what would happen if all the odd numbers were even?

score 0 · Accepted Answer · answered Aug 18 '15 at 14:07

0

You can use the bitshift function in MATLAB. I believe

Recorder = audiorecorder(fs, nbits, nchan);
data = getaudiodata(Recorder, 'int16');
outData = bitshift(data, -1);

Hope this helps.

Dinesh

answered Aug 18 '15 at 14:07

Dinesh Iyer

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Quantizing a audiorecorder sample in MATLAB

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