On Fri, 07 Mar 2003 08:09:20 +0100, Richard Hulme <rhulme_news@yahoo.co.uk> wrote:

>Steve King wrote:

>>

>> So, I went back to it with Cool Edit Pro. The noise reduction module

>> was able to improve the intelligibility at the cost of seemingly

>> unavoidable artifacts. I did four 10 db per pass reductions

>> resampling the noise profile for each pass followed by about 5 db of

>> hard limiting. Better, and if there are no other choices.....?? I

>> guess one would have to see the shots to know if the 'distant' audio

>> with squigly artifacts in the BG would be okay... depending on the

>> purpose, the audiences desire to hear the commentary, etc.

>I think the noise on the track is far too random to be removed cleanly

>with noise reduction (which is why you're getting the squigly artifacts).

>

>I'm no expert on audio processing but here's how I see it:

>

>You have hiss, a high-pitched whine and some rumble. I'd attack them

>one at a time rather than trying to remove them all in one go.

>

>Do a frequency analysis to locate the whine frequencies and use a notch

>filter to remove them (or at least reduce them).

>

>Alter the EQ to remove some or all of the rumble (how much probably

>depends on how much overlap there is between the frequencies in the

>voice and the rumble)

>

>You can probably remove at least some of the hiss using a low-pass

>filter if the track is only voice and not music.

>

>For the rest of the hiss, I think it's probably going to be difficult.

>Maybe you could get an improvement by playing with the EQ again but if

>the hiss is in the same frequency range as the voice (which it almost

>certain is), you'll probably just end up thinning out the voice.

>

>I think it'd be very difficult if not impossible to get a clean

>recording out of this track but you can certainly improve it. The

>question then is whether the improved track is good enough.

>

>Richard.

The Cool Edit noise-reduction is quite effective with hiss,

if not used to the point of leaving annoying artifacting.

Sometimes it is useful to add low-level sound level

reduction (expansion) either manually or with the shaped

expander module in Cool Edit to further reduce noise in the

quieter areas between words. Perhaps a little EQ could be

useful at the end of the process. One cannot remove all the

noise from this clip, but it can be much cleaner. There is

no need to separately remove other noises when doing this...