Low-pass filter for cleaning vocal speech before performing onset detection I am creating a piece of software that detects when speech starts in an audio recording. Before performing onset detection I would like to remove any noise that may cause any false positives. Which would be the best low-pass filter to use for this?

EDIT 1

Maybe I went too far in saying that I am performing onset detection. Basically all I am doing is looking for the first time the amplitude goes above a certain value and taking that as a flag for the start of the envelope. It is simple and crude, but I believe if my low-pass filter successfully removes noise then the onset detection should work. Or am I totally off on this?
The problem is that for speech, noise and speech may well occupy the same frequency bands, so removing an arbitrary band by simple filtering can remove speech as well, which will prevent your detector from triggering, as well as not removing out-of-band noise, which will produce false positives.

So, what you are looking for might not be just a low pass filter, but a Voice Activity Detection algorithm, which is a more sophisticated bit of DSP technology.  There are many research papers on this topic, so it's not a short answer question.