How to perform a Bitwise Operator on a byte array in C#

Question

I am using C# and Microsoft.Xna.Framework.Audio;

I have managed to record some audio into a byte[] array and I am able to play it back.

The audio comes in as 8 bit unsigned data, and I would like to convert it into 16 bit mono signed audio so I can read the frequency what not.

I have read a few places that for sound sampling you perform a Bitwise Operator Or and shift the bits 8 places.

I have performed the code as follows;

soundArray[i] = (short)(buffer[i] | (buffer[i + 1] << 8));

What I end up with is a lot of negative data.

From my understanding it would mostly need to be in the positive and would represent a wave length of data.

Any suggestions or help greatly appreciated,

Cheers.

MonkeyGuy.

dtb · Accepted Answer · 2010-09-03 15:58:45Z

1

This combines two 8-bit unsigned integers into one 16-bit signed integer:

soundArray[i] = (short)(buffer[i] | (buffer[i + 1] << 8));

I think what you might want is to simply scale each 8-bit unsigned integer to a 16-bit signed integer:

soundArray[i] = (short)((buffer[i] - 128) << 8);

alt text

edited Sep 3, 2010 at 15:58

answered Sep 3, 2010 at 15:52

dtb

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1 Comment

monkeyguy Over a year ago

Still getting quite a few negative but a lot of positives now and they're quite high in the range up to the 32,000 mark. The Sample Bit Rate is apparently 16000hz.

Marco · Accepted Answer · 2010-09-03 15:51:36Z

0

Have you tried converting the byte to short before shifting?

answered Sep 3, 2010 at 15:51

Marco

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2 Comments

dtb Over a year ago

You can't shift bytes. If you use << on a byte, it's automatically converted to an int/Int32.

monkeyguy Over a year ago

Yes I do it right before the bitwise conversion on; soundArray[i] = (short)(buffer[i] | (buffer[i + 1] << 8));

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