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Unofficial VirtualDub Support Forums > VirtualDub Filters and Filter Development > Noise Cancellation

Posted by: powershotfan Apr 16 2003, 03:48 AM

I have shot some movies with an S230, and in quiet environments, you can hear a fluttering sound that is common to these cameras. It is cyclical. Is there any noise cancellation or filtering techniques that can mitigate this and reduce it? I am confused on how to use the audio filters on Virtualdub, so If someone could walk me through in as detailed as possible, that would be great. Thanks.

Posted by: ChristianHJW Apr 16 2003, 11:21 PM

I am not sure if this could be filtered out at all, as its likely not a narrow band signal .....

Posted by: Kippesoep Apr 17 2003, 01:03 AM

If it is reasonably narrow-band and you know the frequency limits of the sound, it can be filtered out using the advanced filters. The graph to do this would need the following elements:
- input
- split
- mix
- highpass
- lowpass
- ouput

Connect the output pin from "input" to the input pin for "split". Connect "split" output pin 1 to the input pin for "highpass" (set this to cut off everything below the highest noise frequency). Connect "split" output 2 to the input pin for "lowpass" (set this to cut off everything above the lowest noise frequency). Connect the output pins from highpass and lowpass to the input pins for "mix". Connect "mix" to "output"

That will eliminate a certain frequency range. As ChristianHJW said, though, if the signal is not very narrow-band or if the frequency is also used by another sound, then this won't help you much...

Posted by: phaeron Apr 17 2003, 02:04 AM

You cannot make a usable notch filter with the internal VirtualDub audio filters. The reason is that the lowpass and highpass FIR filters do not have sharp enough falloff for this -- at 129 taps the transition band for each is 1.3KHz. I'm betting the offending noise band in the audio track is narrower than 2.6KHz. The shallow falloff is a problem whenever you try to combine filters like this, but on the other hand it sounds better than a cliff and it avoids numerical accuracy problems.

I need to make the tap count configurable in 1.5.2. The highpass filter is nearly useless with such a large transition band, although the lowpass is usable to some extent.

Posted by: David.Bucci Apr 17 2003, 04:10 AM

QUOTE (powershotfan @ Apr 15 2003, 10:48 PM)

Is there any noise cancellation or filtering techniques that can mitigate this and reduce it?

Yeah, what phaeron said.

Seriously, did you get this answered elsewhere? I remember a similar thing in the last couple of days, recommending you save out the audio to a .wav, and use http://audacity.sourceforge.net/, open source audio editor, to isolate and cancel out the sound. I've had good luck with its internal noise cancellation tool on all kinds of rhythmic, frequency-specific sounds, as well has hiss, buzz, even audience coughing.

And if you need to get more agressive, Audacity supports any VST filter, there are plenty of free notch filters out there.