Software audio filtering

Ashton · Post by **Ashton** » Fri Dec 27, 2002 2:55 am

I know this is the video forum, but there is no audio forum, and its a technical question and I dint know where else to pu this.
If I were to recording from a live action source using a mic onto a computer, and then doing what I liked with it afterward, how I can I filter the audio so that it sounds like as good as movies do? (IE none of that background neise and all that) Is a special mic required?

klinky · Post by **klinky** » Fri Dec 27, 2002 3:00 am

No audio forum???

http://www.animemusicvideos.org/phpBB/v ... m.php?f=26

I believe you need a GOOD mic, so that

A) Doesn't sound like crap
B) Doesn't pick up your brother making farting noises from 20ft away :\

I don't know of any software that could filter out background noise.

Also it would probably be best to record away from the computer. Since computers are noisey SOBs.

~klinky

trythil · Post by **trythil** » Fri Dec 27, 2002 3:15 am

Um, there's an "Audio Help" forum...

Anyway, noise in audio comes from a lot of places. Some of it comes from the recording device; this can be compensated for by running denoise filters on the audio (most audio editing systems have such a feature).

However, another significant source of noise that is much harder to reduce comes from the hardware itself, and the nature of analog->digital conversion. The hardware noise is due to a number of factors, such as electromagnetic radiation from other components in your system that interfere with the sound board. (This is why a lot of people like external sound units.)

As far as the analog->digital conversion goes: Computers are digital machines, and sound is an analog phenomenon. Mathematically, what you're trying to do when you do A->D conversion is trying to use a finite number of digits (and hence limited precision) to represent an infinite number of digits (infinite precision). This happens all the time with computers: even something as simple as representing 1/10th of a dollar (i.e. $.10) is impossible to do completely. (See what happens when you try to represent 0.10 in binary.) But I digress.

This is quantization, and quantization with low precision introduces noise. For example, if you quantize a continuous sine wave

with a very rough quantization function (nearest integer)

you get nasty waveforms. When played back, these produce "clinking" sounds. This is an exaggerated case, obviously, but it shows you another source of noise.

The only thing that you can really do cheaply to denoise audio is software processing. Anything else requires better hardware.

trythil · Post by **trythil** » Fri Dec 27, 2002 3:17 am

Damnit, I forgot to change my Maple command for that first image to scale to -4..4 on the y-axis. Oh well. You get the point.

trythil · Post by **trythil** » Fri Dec 27, 2002 3:26 am

...I need to stop triple-posting and get my thoughts together in ONE post...

Anyway. Denoise filters can be readily found all over the place -- two cheap sound editors (Audacity and GoldWave) have such filters. If there's a really high-pitched sound in the audio (or, conversely, a really low-pitched sound), you may be able to lessen it by playing around with equalizer settings.

However, again, if your workspace is electrically noisy, or if your soundcard has crappy A->D and/or D->A converters, you won't really notice much.

madmallard · Post by **madmallard** » Sat Dec 28, 2002 11:50 am

like a creative labs product, for eaxmple. ;p

Ashton · Post by **Ashton** » Wed Jan 01, 2003 9:58 pm

Wow Trythil, thanks. Im actually more than willing to buy an external mic, I just want some kind of a suggestion regarding what I should buy. Lets say that my budget is 50 dollars, will I be able to so it on that budget?