Re: [linux-audio-user] Noise removal, what filter is best?

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Subject: Re: [linux-audio-user] Noise removal, what filter is best?
From: Tim Beauregard (helycos_AT_lycos.co.uk)
Date: Tue Aug 26 2003 - 12:32:13 EEST


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Anahata wrote:
| Noise removal tools like that in audacity are for removng a constant
| background hiss or hum and would not be suitable for an occasional loud
| sqeak. I'm surprised that gramofile does not do anything for it, but I

I could wade through all the filters and tweak them til I get a (near)
satisfactory result.

| think your best bet in this case may be to use a sound editing tool like
| audacity and manually cut the noise blips. If they are much highe
| amplitude than the normal sound they should show up on the display;
| otherwise you'll just have to locate them by ear. When you find one you
| can either cut the noise out (shortening the recording by the length of
| the section you've cut out) or use the amplitude envelope tool to make a
| rapid fade out/fade in over the noise. The first method will cause a
| time discontinuity: the second may cause an audible droput in the sound.
| It depends on the nature of the recorded material and the length of the
| noise burst and you'll have to experiment to see which is the least
| objectionable.

Good advice, sometimes I can see the sound, sometimes not. Will try the
fading technique.

| If the noise is at exactly one frequency, it may be possible to select
| a short section containing the noise and apply a filter with audacity,
| with a deep notch at the frequency of the noise. I wouldn't advise
| applying such a filter all through the recording because it would
| probably not sound very nice, and it's a pity to spoil a minute or good
| sound just to reduce the effect of a fraction of a second of noise.
| Again you'd have to do this for each noise burst, but with a bit of luck
| (i.e. if the frequency is the same each time) the same filter setting
will
| work on each one.

And this is worth a try too. Lots to get my teeth into.

Thanks aplenty.

Tim
|

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