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2 byte integer / .wav data -  sample value  conversion

Posted on 2003-03-10
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Last Modified: 2009-07-29
Hello ,

I'm trying to simply display a wave file graphically ...
I'm stuck in reading the  bytes and convert it to a sample value :
ie. for 16bit PCM , I have to convert 2 bytes to a value ranging from -32768 to 32767

so , I have the 2 byte values , ranging from 0 to 255 which represent the 65536-step value , but I dont know how to convert them ,
I guess i could just multiply them, so I have 256 * 256 (=65536) possible values ,
but that must be not correct , cause I have values like (0 and 9) or (0 and 200) which is multiplied =>> 0 * 9 = 0 ???

My guesss is that I have to read as a byte ranging from 0x7FFF(=32767) to 0x8000(-32768),
a 2 byte integer ... but
how do you do that ??
how do you read 2 byte integers ??
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Question by:DotNetSlet
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2 Comments
 
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Accepted Solution

by:
Arthur_Wood earned 225 total points
ID: 8104136
what is normally done is to treat these as a "HIGH ORDER" and "LOW ORDER" pair, and then MULIPLY the High-Order value by 256, and Add the Low-Order value, ending up with a value formatted as HHHHLLLL.

AW
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LVL 4

Expert Comment

by:Nebulus_
ID: 8104271
Maybe I don't understand well what you need. But if you
need to read a file as array of short values here is a solution:

System.IO.FileStream a = System.IO.File.OpenRead(@"C:\Program Files\NetMeeting\Blip.wav");

short[] c = new short[50];
byte[] bp = new byte[100];
a.Read(bp, 0, 100);

fixed(byte* pSrc = bp) {
  fixed(short* pDst = c) {
    byte* ps = pSrc;
    short* pd = pDst;
    for (int n = 0; n < 50; n++) {
      *((short*)pd) = *((short*)ps);
      pd ++;
      ps += 2;
    }
  }
}
a.Close();
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