Tilted Forum Project Discussion Community - View Single Post - What does anti-aliased mean?

digby · 07-21-2003, 10:37 AM

woo hoo! physics lecture time! since everyone else answered the practical side, I'll try to explain what's going on behind the scene.

-note: if you don't care about sampling and recovery, and other aspects of applied digital electronics, you can skip this post and save yourself a headache.

Aliasing is an undesirable by-product of all digital to analog conversions. Because all data is stored at discrete values, you get that "jaggedness" in what would otherwise be a continuous function.

For example, imagine a sine wave. When sampled and restored, you would have something that looks like a bunch of ascending and descending stairs. From a mathematical standpoint, this is a construct of an infinite number of odd harmonics (multiples of the fundamental frequenct of our sine wave).

An anti-aliasing filter is a low-pass filter that (in theory) begins to operate just above the frequency of our original sine wave. This removes all those extra, unwanted frequencies and gives us a very close approximation of our original input signal.

I apologize if this isn't the most thorough explantion. I'm trying to pack about 4 weeks of digital theory lectures into a short little paragraph. Let me know if you need clarification.

[edit]I know all that stuff, but I still can't spell.[/edit]

07-21-2003, 10:37 AM	#8 (permalink)
digby Crazy Location: Ahh, the lovely South	woo hoo! physics lecture time! since everyone else answered the practical side, I'll try to explain what's going on behind the scene. -note: if you don't care about sampling and recovery, and other aspects of applied digital electronics, you can skip this post and save yourself a headache. Aliasing is an undesirable by-product of all digital to analog conversions. Because all data is stored at discrete values, you get that "jaggedness" in what would otherwise be a continuous function. For example, imagine a sine wave. When sampled and restored, you would have something that looks like a bunch of ascending and descending stairs. From a mathematical standpoint, this is a construct of an infinite number of odd harmonics (multiples of the fundamental frequenct of our sine wave). An anti-aliasing filter is a low-pass filter that (in theory) begins to operate just above the frequency of our original sine wave. This removes all those extra, unwanted frequencies and gives us a very close approximation of our original input signal. I apologize if this isn't the most thorough explantion. I'm trying to pack about 4 weeks of digital theory lectures into a short little paragraph. Let me know if you need clarification. [edit]I know all that stuff, but I still can't spell.[/edit] __________________ mmmm.... pudding Last edited by digby; 07-22-2003 at 05:59 AM..