Down converting Equation Please

Started by ahmad chaudhary May 21, 2007
Hi every one,

First my apology for not using/knowing matlab termnalogy.

One question
how could I down convert in software.
Suppose I have a data from real world @Sampling rate 100,000 per/sec.
I know It has ultra sonic voice in it.
How could I convert it to 20000 per/sec.
Do I just drop every other signal? making it 50000?
Can some one writhe me an equation? Since I don't know matlab.
I will use C to convert that equation in my code.