Need help removing "nail scratching"-like sound on a capture

[Chainmax]

I am trying to clean up the audio on a capture and already used GoldWave's Hum removal denoise preset and the pop/click remover at passive preset.
The file sounds great now, but while hearing bits of the audio, I found one segment (of which I guess there are several), where a nasty "nail scratching on a chalkboard"-like can be heard. Hearing the whole ~76min sound file is not really an option, so I wanted to know if you could recommend me a method to remove those artifacts automatically. Using GoldWave tool it would be preferable, but alternatives are welcome. I can upload a short sample with the artifact for assessment if needed.

[setarip_old]

Hi!

I'd suggest you read this thread(That you contributed to), with an eye toward using "Audacity" :

http://forum.doom9.org/showthread.php?t=113252

[AVIL]

Hi,

¿This noise is present in original sound?. Sometimes sound filters (especially fft ones) brings more ugly noise than removed. If so you must use softer parameters to "noise hum removal" and "pop/clik removal".

If noise is in the original, then you can try a lowpass filter but, probably, you must locate noise zones and treat it individually.

Good luck

[Chainmax]

setarip_old: I didn't know more replies after mine appeared on that thread, thanks for the heads-up :).

AVIL: yup, the noise is present in the original file. A lowpass cuts off frequencies above or below a defined threshold, right? Would that really help in this case? If so, do you have any idea what kind of lowpass to apply?

[AVIL]

Hi,

With Goldwave, you can play with the equalizer, to ensure that noise is related to a particular band of frecuencies (if noise spreads at all the band, method isn't suitable). You can play also with the graphic equalizer for more fine tunning.

If found that noise is of high frequency (as I think), I recommend a lowpass filter (Low/Highpass filter in Goldwave, also Bandpass/stop filter as they are very similar).

If you have a particular zone of the sound whith olny noise (no real sound) you can use "Noise reduction" filter by previously copying "noise only" zone in the clipboard and checking "use clipboard" option as parameter of the filter.

In any case, is better to do selective denoising.

Good luck.

[Chainmax]

I uploaded two clips (original and filtered, ~7MB) that show the issue. You can download them here:

http://rapidshare.de/files/28063117/Scratching_sound_samples.rar.html

[AVIL]

Hi,

The noise is a complex one. So it's difficult eliminate them without damage for good sound. I have any result with Goldwave's smoother filter length 12. I have also better sound eliminating higher frequencies. But to preserve the rest of the sound it's neccesary to limit this filters to noised zones. ¿How to locate them?. You don't have to listen all the clip. You can locate automatically. With edit menu, select only left channel and invert them. Select both channel and use stereo/channel mix. As your sound is mono, normal sound is cancelled. Only remains the ugly noise in a very evident manner. In fact you could (merging inverted version of the noise) select the noise whith minimal amplitude between channels.

Anyway, you must operate on original sound. After denoise them you can do the rest of the denoising (i haven't heard pop/click noise).

Good luck.

[Chainmax]

I'll try to do what you're saying, thanks for the suggestion. So, you're saying the sound is actually just two channel mono instead of real stereo? How did you find that?

[setarip_old]

If, as done by "AVIL", you load an audio file into GoldWave - and look at the bottom of the primary window...

[AVIL]

Hi,

I saw sound is mono viewing sound with a very high zoom. Waveform of left and right channels are equal (not in the damaged part, of course). In a true stereo sound, waveform of two channels looks different even whit a low zoom.

In noised zones, original sound is distroyed. I can't extract good sound of it even strenghting noise reduction parameters (I use goldwave and audacity). Then, I think solution es eliminate it. Tipical noise appears as a burst. I`ve done a fade out between the last peak before the noise and the middle of the burst and a fade in between the middle of the noise and the next peak of good sound. Efect is good for me. I appears more natural than simply deleting the noise.

Good luck