Tech: Removing hum from old tapes

28 Aug 14 - 03:31 PM (#3654653)
Subject: Tech: Removing hum from old tapes
From: GUEST,CJB

I have a number of off-air reel-reel recordings that I'd like to rescue by digitising them. I have digitised some of them them to WAV files. BUT they all have an amount of mains hum on them. Audacity Spectrum Analysis shows that this is around 50 KHz plus harmonics. The strongest harmonic is 200 KHz, then 100 KHz, then 50 KHz, then 400 KHz. But these are all +/- 10 KHz - it is a noisy hum.

If I use a Single Parametric effect on these frequencies in turn (at about -30db) the hum is nullified, but so is the audio!! Boosting the audio volume only brings back the hum. And the audio also sounds strange without any depth.

I have also tried notch filters - again on the above frequencies. But even being very selective with a high Q factor the result is the same - strange sounding audio.

Then I tried highlighting 0.5 sec. of noise (from a gap in the actual performance recording). Then I 'taught' Audacity what that noise represented. Then I applied the associated noise filter. But whilst the hum disappeared in the quiet parts of the recording as soon as the loud parts were played so did the hum. The hum had been filtered from the quiet parts, but not where it was embedded in the loud parts. This resulted was an audible pulsing effect.

What do folks here recommend please?

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28 Aug 14 - 04:55 PM (#3654691)
Subject: RE: Tech: Removing hum from old tapes
From: Bonzo3legs

Adobe Audition CC I'm afraid (expensive) should do a good job, it can selectively remove unwanted noise.

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28 Aug 14 - 04:57 PM (#3654692)
Subject: RE: Tech: Removing hum from old tapes
From: Bonzo3legs

Adobe Audition CC

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28 Aug 14 - 05:21 PM (#3654702)
Subject: RE: Tech: Removing hum from old tapes
From: GUEST,Grishka

The Audacity method you described will never work miracles, but can be reasonably successful, depend a lot on the exact section you use for "teaching". Theoretically, quiet sections make best candidates, but since these are never "completely" quiet anyway, some experimenting may yield surprising results. The gap may have been the wrong choice because part of the hum is due to the actual recording.

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28 Aug 14 - 05:48 PM (#3654714)
Subject: RE: Tech: Removing hum from old tapes
From: olddude

Try kristal its free

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28 Aug 14 - 05:49 PM (#3654715)
Subject: RE: Tech: Removing hum from old tapes
From: olddude

Kristal audio engine

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28 Aug 14 - 08:00 PM (#3654758)
Subject: RE: Tech: Removing hum from old tapes
From: Nick

Or Reaper. Has some decent filters including reafir (try reafir noise reduction in google for a lot of relevant stuff.

I've used it for that very reason and it does have some reasonable results. Reaper is free to download and trial and is uncrippled. It was good enough that I happily bought it and have used it for a long time

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28 Aug 14 - 08:18 PM (#3654768)
Subject: RE: Tech: Removing hum from old tapes
From: olddude

agreed its a good one for sure

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29 Aug 14 - 02:51 AM (#3654819)
Subject: RE: Tech: Removing hum from old tapes
From: Richard Mellish

The built-in sound systems on many computers are not very good for this purpose. Unless the original recording quality is poor it's worth using a device with some claim to quality for analogue-to-digital conversion; either an internal sound card or an external USB audio interface.

BTW that hum is 50 Hz plus harmonics (and across the Pond it would be 60 Hz), not 50 kHz.

The sound-editing software should offer various filtering options. If it doesn't allow you to apply a set of notch filters at 50 Hz, 100 Hz etc, try another one that does.

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29 Aug 14 - 02:57 AM (#3654822)
Subject: RE: Tech: Removing hum from old tapes
From: Jim Carroll

Adobe Audition can work wonders but you have to remember that anything you do to sound is going to distort the original sound to some degree or other.
Jim Carroll

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29 Aug 14 - 05:12 AM (#3654850)
Subject: RE: Tech: Removing hum from old tapes
From: Mr Red

If it is on the tape you have a problem.
If it is in the digitising process there are things you can do.
1) check your earth loops.
2) run on batteries where possible (I do this for cassettes.)
3) I run the laptop on battery.
4) I have a Sweetex USB audio dongle which seems to isolate the audio better than on-board audio, but it is not entirely perfect. But any that brag of optical isolation will be best.
5) I put the laptop on a earthed metal plate (Tower side panel)

now the tape
If it was important enough I would investigate the possibility of subtracting the hum. (invert and add in Audacity, Cool Edit etc)
If you have enough footage that is without the desired audio, lead-in etc, then try to generate a waveform that is the same as the hum and subtract (invert & add). But it has to be said this is going to be an iterative process and need tweaking for level on each harmonic and phase for each harmonic (fundamental included). Being methodical would pay dividends. How important is it? How much patience have you got?
Thought not!

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29 Aug 14 - 05:27 AM (#3654854)
Subject: RE: Tech: Removing hum from old tapes
From: Mr Red

of course the subtracting wheeze assumes you have the exact frequency right, and the tape hasn't stretched in places and the reel-reel is precise, with a clean capstan. But done in sections, it is doable. Just time-consuming and ultimately the best you can do.

Notch filters remove all at those freqencies you choose to remove. Given that music energy is going to be present from 100Hz up it is always going to disadvantage the result.

For speech I cut it down to 400 - 4KHz if it is the best I can do. It sounds like a telephone recording. If the contents are important enough, the message gets through.

Some of my worst efforts can be heard at StroudVoices.co.uk - but for that website - content is king. Quality just has to be enough. I have captured the moment and I can't get it again, usually.

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29 Aug 14 - 09:34 AM (#3654898)
Subject: RE: Tech: Removing hum from old tapes
From: GUEST,Jonny Sunshine

It's worth experimenting with settings if you use the noise reduction in Audacity- especially if it results in pulsing sounds, the attack and release settings should allow you to make that less noticeable. Also, it's better to leave a bit of the original noise than to overdo the reduction which will result in all kinds of odd, artificial artefacts in the signal (a friend of mine describes them as "space munchkins")

If you're taking a noise sample from an old tape recording, it won't be constant throughout the recording- ideally you'd want to sample from the gap between each track (or any time you have a quiet bit) and do it section by section. Sadly, there's no easy quick way to do it- it depends how much time you can spend on it, and how important the recording is.

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29 Aug 14 - 10:11 AM (#3654909)
Subject: RE: Tech: Removing hum from old tapes
From: Anglo

I've used SoundSoap for a long time and I'm very happy with it. You have to find a 2 sec sample of just the noise you want to eliminate (easy on a cassette tape) and go from there.

Originally from Bias, now defunct, it is still supported by Soiundness. Versions for Mac and Windows. I'm on a Mac and I bought it from Bias a while ago. Never regretted the expenditure, except to note that the last time I looked, it was bundled free with Toast, CD burning software which I've also used for a long time.

I think you can get a free trial.

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29 Aug 14 - 09:13 PM (#3655088)
Subject: RE: Tech: Removing hum from old tapes
From: Nick

The reafir thing I mentioned is an example of a subtractive process. You find a piece of tape which just has 'hum' in it and save that in the filter. You then subtract it from the whole.

It does a decent job.

I recorded something a few weeks ago and the result had a large amount of background hum. If you are interested I could probably do you a 'before' and 'after' to demonstrate.

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30 Aug 14 - 04:53 AM (#3655149)
Subject: RE: Tech: Removing hum from old tapes
From: treewind

This should be a straightforward job for Audacity's noise removal tool, as long as you can get a good sample of the hum by itself, and as long as the hum is constant in level though the recording.

It's more sophisticated than a series of notch filters, which would indeed impair the sound quite badly.

Jonny Sunshine (above) has good advice too.

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02 Sep 14 - 05:11 PM (#3656237)
Subject: RE: Tech: Removing hum from old tapes
From: Mr Red

not just constant level, constant frequency. The Mains will be constant enough, but the tape may not be. The apparent frequency (and hence phase) will drift up or down with the stretched parts of the tape.

"noise reduction" in Audacity has not worked for me that well. What any subtractive process will do is increase the hiss because it is not coherent, by its nature it is random. Adding random to random is random X2. So you end up cutting the high end anyway.

Just a thought, but if you are patient enough you could try notch filters in all the silences. Works best on speech and acapella. Music tends to be pretty much "on all the time" so the effect would be very noticeable even if you found any relative silences. There is a lot of "perception" in audio, hum in the quiet sections dominates, but is "relative" in the louder passages. The wheeze above can work, I do it if it improves the overall result.

Best of luck.

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02 Sep 14 - 05:42 PM (#3656253)
Subject: RE: Tech: Removing hum from old tapes
From: Amos

Yes--SoundSoap is a winner at this sort of thing.

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03 Sep 14 - 12:42 PM (#3656548)
Subject: RE: Tech: Removing hum from old tapes
From: GUEST,CJB

Thanks for all of your advice. Here is what I did:

From a totally un-listenable reel-reel tape (50 years old) copied to a cassette tape - this latter was recently digitised. The hum actually came from the dubbing onto the cassette. The reel-reel tapes are long out-of-reach. But the hum was so noisy that the music could hardly be heard. However a combination of Reefer (using ReaFIR) and then Noise Removal on Audacity - and the result isn't bad. Some links:

http://homerecording.com/bbs/user-forums-brand/dont-fear-reaper/noise-reduction-reaper-269007/

Basically I had a WAV file from the cassette tape. This I read into Reefer. Found a gap in the recording where the hum only was present - actually the gap created by the cassette turnover event. Using Reafir I created a noise profile and applied that to the recording. I saved the result as a FLAC file.

I wanted to repeat this for the residual hum. But Reefer was producing a crackling sound when I re-opened and tried to play the FLAC file - so I abandoned that idea.

I then read the FLAC file into Audacity. I applied Normalisation, Pop Removal, and a speed decrease of 2% (Reefer didn't seem to allow for these).

Then I found the same gap with the hum and copied this into a new file with Audacity. Then I scanned that with the (Nyquist) Noise Removal effect. Then I applied that new profile to the whole file.

Finally I saved the result as WAV. FLAC and MP3 (320 kbps).

It is the latter which is uploaded here:

London Folk Song Cellar programme 10 (of 39).

LFSC 10 - TD 115636.37 - RMcL c4 (320)

https://www.firedrive.com/file/59103CF9FBE1E4A4

https://www.firedrive.com/file/02EB57D94EC51E00

CJB

P.S. I will also give SoundSoap a try later.

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03 Sep 14 - 01:16 PM (#3656565)
Subject: RE: Tech: Removing hum from old tapes
From: GUEST,CJB

Hmm - SoundSoap appears to be only available for Macs and Win XP!! The latest review on CNET is dated 2005. Also it doesn't work with Audacity. And there is no 'try before purchase' option. Or do folks know different? Thanks.

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14 Jun 16 - 12:37 AM (#3795471)
Subject: RE: Tech: Removing hum from old tapes
From: cnd

So I don't know if this questions was answered or not in this method because I don't have the time to read it right now, but with Audacity, you can find an area of the music with no singing or music (what would be silent if there was no hum) and then highlight that with the cursor. Then hit "effects" and select "noise removal." First, hit the box that says "get noise profile," and then highlight the entire recording and go back to effects and noise reduction and hit "ok" this time. That would get rid of the effect on a recording at least. It also works with record clicks.

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14 Jun 16 - 11:28 AM (#3795589)
Subject: RE: Tech: Removing hum from old tapes
From: punkfolkrocker

Some years ago I plugged the output of a valve guitar amp modified for direct recording from the power tubes and transformer,
into a PC running audacity.

Tee amp was turned up to every dial on 10, and the guitar was a reasonable telecaster copy..

The recording sounded as powerful as expected, but so too was the hum from standing in front of a CRT monitor.

The audacity noise reduction was as effective as cnd says,
but it also significantly affected the same frequency range as the hum.

Something to be aware of.

In my case, the result sounded as though the amp had been fitted with a vintage treble booster circuit.. so win.. win... 😎

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