Tech: How to Remove Noise from recordings

Subject: Tech: How to Remove Noice
From: GUEST
Date: 04 Jul 12 - 02:36 PM

Hi, Can you guys help me? Please tell me how to remove or reduce noise of mp3 files? I need some patented tools / program and want to buy its license. But i can't find the right place for this I have got some places but all of them are really scammers and don't have the broker address actually.

Subject: RE: Tech: How to Remove Noice
From: treewind
Date: 04 Jul 12 - 03:24 PM

The noise removal tool in Audacity works well for noises like hiss or AC hum. And it's free.

Subject: RE: Tech: How to Remove Noise from recordings
From: Jim Carroll
Date: 05 Jul 12 - 04:24 AM

Adobe Audition is a tremendous programme - for basic noise removal to complex fine-tuning.
Remember that all noise removal is a swings-and-roundabouts process which invariably effects the quality of the recorded sound.
Jim Carroll

Subject: RE: Tech: How to Remove Noise from recordings
From: Acorn4
Date: 05 Jul 12 - 04:45 AM

Apparently you can actually add "Tape hiss" to bring back the feel of those old cassettes.

Subject: RE: Tech: How to Remove Noise from recordings
From: GUEST,Charles Macfarlane
Date: 05 Jul 12 - 06:34 AM

I've tried two or three commercial software programs, which I still use even though I purchased them a decade or more ago, so be aware that what follows may be out of date.

Dart, I think it was called, was utterly useless.

DCArt can be particularly good at interpolating over vinyl scratches, though the results are often highly dependant on the start and end points chosen for the interpolation, slight changes in these causing big changes to the results. It has quite a wide range of filters, etc, and in particular can filter based on a sample, which is particularly useful for turntable rumble. However, the software is somewhat 'quirky'. In particular, as the file is edited in situ, with its time and date stamp being altered accordingly even if you undo all changes, you should always back up a file BEFORE loading it into DCArt.

SonicFoundry (as was) / Sony (now) Sound Forge is also quite good, with a good selection of filters, etc. However, be aware that this software has potentially hidden expenses - for example, the basic program may cost so much, a filter to read in MP3 files, so much extra, etc. This approach to marketing by Sony completely alienated me, which is one reason why I'm still using a decade-old version.

As for the noise itself, generally, it's better to avoid it getting into the recording in the first place, than to try to remove it afterwards, as this inevitably will affect the wanted part of the recording to a greater or lesser extent - that is it becomes a question of whether the noise in the recording is worse than the wanted part of the recording would be after treatment to remove the noise. What can be done depends very much on what sort of noise it is, and the OP is not specific about this.

Extraneous noise picked up by a microphone is very difficult or impossible to remove. I have a recording off the soundtrack of Don't Look Back of Joan Baez, then Dylan's girlfriend, singing part of the then unfinished Percy's Song in their hotel bedroom. Her rendition of it was utterly beautiful, but during it Dylan is tactlessly pounding away at a typewriter. I've tried everything I know to remove Dylan's rudeness from the recording, but without success.

Tape hiss is comprised of mostly high-frequency random noise, and many software programs have a tape-hiss filter specifically for removing this. However, it's nature means that it can not be completely removed from a recording without adversely affecting the top-end, particularly transients, etc - it's a compromise, a question of removing as much hiss as is required to reduce its prominence in the recording without audibly degrading the wanted sound. I suspect that early Fleetwood Mac CDs of their eponymous album (7599-27241-2) and its successor Rumours (7599-27313-2) were over-treated in this respect, and, compared with the original vinyls, they sound as though the speakers are behind heavy drapery - muffled and lacking in transients. By contrast, those tracks which are also on the Greatest Hits CD (7599-25838-2) sound fine on that. I have read that other masterings of those albums do not suffer from this, but not having heard them, cannot comment.

Vinyl scratches are usually of such short duration that they can be edited out of the waveform, usually and preferably by software interpolation, failing that simply by chopping them out. However, this doesn't always work, some types of music, for example pipe music, being particularly difficult to fix. Usually the best approach with the latter is to replace the affected part of the waveform with an intact identical piece of waveform from close by.

Vinyl wear and dust noise is best removed by cleaning the vinyls before recording them, but failing that, or for whatever remains, the problem becomes similar to tape hiss, and again many programs have a specific groove-noise filter. Again the trick is apply just enough to reduce the prominence of the noise without audibly affecting the wanted sound.

Turntable rumble can be tricky to remove. The approach I use is to sample it from the lead in and lead out of the vinyl, and use the sample to create a specific filter, which DCArt can do. However, as with all of these things, it's a question of how much one can reduce the prominence of the noise without audibly affecting the wanted sound.

Mains hum can be tricky to remove. If it's just a pure sinusoid at 50 or 60Hz, in principle that should be treatable by a suitable filter of that frequency, and again software programs often have such a filter, and again it's a compromise between reducing the hum and audibly affecting the rest of the sound. However, mains hum is often not a pure sine wave, but has many harmonics, etc. Many years ago I bought off Derek Brimstone a commercial audio-cassette of one of his live performances, which has quite prominent mains hum from the PA. When later I digitised it, I wasn't able to find a way of removing the hum from the wave file.

Subject: RE: Tech: How to Remove Noise from recordings
From: GUEST,Charles Macfarlane
Date: 05 Jul 12 - 06:36 PM

As an afterthought, if someone wants advice on digitising and restoring old vinyls, I have a webpage on the subject:

Vinyl Restoration

Subject: RE: Tech: How to Remove Noise from recordings
From: treewind
Date: 06 Jul 12 - 06:56 AM

"Mains hum can be tricky to remove"

If you can get a short sample of it without other sounds present, the Audacity noise removal tool (which uses the same mechanism you have described for turntable rumble) should reduce the fundamental and the harmonics.

Subject: RE: Tech: How to Remove Noise from recordings
From: Bernard
Date: 06 Jul 12 - 07:22 AM

It's very important to convert MP3 files to WAV before working on them. Not because it improves the quality (which it cannot), but because any subsequents 'saves' would not progressively reduce the audio quality as MP3 compression algorithms would do.

Once you have finished editing, then you can convert back to MP3 - but keep the WAV file as your backup.

Subject: RE: Tech: How to Remove Noise from recordings
From: GUEST,Charles Macfarlane
Date: 06 Jul 12 - 07:34 AM

> From: treewind
>
> Audacity noise removal tool

Thanks, that's useful to know, and of course one could do the same with DCArt.

I can't remember whether I've already tried this on the Derek Brimstone AC file - I tried everything that occurred to me at the time. I'm tied up for the forseeable future, but I'll give it a go sometime.

Subject: RE: Tech: How to Remove Noise from recordings
From: GUEST
Date: 06 Jul 12 - 08:00 AM

> From: Bernard
>
> It's very important to convert MP3 files to WAV before working on them. Not because it improves the quality (which it cannot), but because any subsequents 'saves' would not progressively reduce the audio quality as MP3 compression algorithms would do.

Yes, good point. It should always be remembered that MP3 compression is a 'lossy' algorithm - that is, each time a file is saved the algorithm throws some of the sound away.

Subject: RE: Tech: How to Remove Noise from recordings
From: GUEST,Charles Macfarlane
Date: 06 Jul 12 - 08:02 AM

Forgot to sign the above

Subject: RE: Tech: How to Remove Noise from recordings
From: Jim Carroll
Date: 06 Jul 12 - 09:04 AM

A thought - we are constantly preparing our large collection of recordings for depositing in an official archive and have been strongly advised to do as little as possible to the original recordings in light of the fact that technology is constantly developing and what is not possible today may well be in say ten years time.
If your recordings are archivable, it is well worth bearing this in mind.
Charles Macfarlane
Thanks a million for your site address; I should think it will be a great help to our work
Jim Carroll

Subject: RE: Tech: How to Remove Noise from recordings
From: GUEST,Charles Macfarlane
Date: 06 Jul 12 - 10:53 AM

> From: Jim Carroll
>
> A thought - we are constantly preparing our large collection of recordings for depositing in an official archive and have been strongly advised to do as little as possible to the original recordings in light of the fact that technology is constantly developing and what is not possible today may well be in say ten years time.

Yes, another good point. If one is archiving anything, it is important to keep the original digitisation files intact and work only on copies. It's similar thinking to the advice on my Vinyl Restoration page to record the vinyls both before and after washing/cleaning, in case the latter process degrades the vinyl in some way.

> Charles Macfarlane
>
> Thanks a million for your site address; I should think it will be a great help to our work

You're welcome, that's why it's there.

One point I haven't mentioned on that page: 78rpms and earlier record types. Anyone planning to restore anything older than 33 & 45rpms should investigate how to clean the record on something that doesn't matter, in case their proposed cleaning technology adversely affects the material upon which the recording is pressed. In particular, ISTR that the Isopropyl Alcohol (IPA) solutions commonly used with 33 & 45s will degrade 78s and older materials.

When drawing up that page, ironically my least valued recording was the first to be done, because I used it as a guinea-pig to ensure that the process was going to work as I hoped and expected.