Removing Hum From Old Tapes

[Stephen Byers]

Might I suggest that a new Tech. Forum be created here.

Meanwhile 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.

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 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?

[Dan S]

I usually try EQ but it's always a trade-off, being satisified with only removing some of the hum and not trying to remove all of it and ending up ruining the overall sound of the recording.

Sometimes it seems impossible to remove all the hum. Well, not necessarily impossible. Organisations such as the BBC have access to better equipment than most of us so they can probably work miracles where most of us can't.

Sometimes it's better to leave the sound alone despite the hum rather than leave it sounding overprocessed and strange.

Whatever you do, it's a good idea to keep an untouched copy of the file as wav (or convert it to flac if you want to save some space), because at a later date there may be better software that'll give better results.

[Deleted]

I've had the same problem as Stephen with old recordings (namely low background hum) and the same trouble removing it. So I can relate to this one. The solution would seem to be a program which isolates certain frequencies within a narrow and specific range and removes them without also taking out the surrounding frequencies. Going down the EQ route is never wholly satisfactory as I find it's always a trade off between taking out enough of the hum (or hiss in other cases) and not taking out too much of the recording with it! So I'd also be interested to know if there's any effective programs freely available that can sort this out (or at least to a higher degree than managed so far).

[Greg H]

Aug 27, 2014 0:34:00 GMT Dan S said:

Whatever you do, it's a good idea to keep an untouched copy of the file as wav (or convert it to flac if you want to save some space), because at a later date there may be better software that'll give better results.

This is sage advice! If it might be rare, keep the original and an uncleaned version of your transfer in lossless format such as WAV or FLAC.

I have heard a few horror stories about old time radio shows being over-vigorously cleaned and the originals being disposed of. I am sure most members here are fully aware of this problem, but just on the off chance that someone reads this advice who is in this position, I thought I would put it out there

[John Smith]

PM me an example if you like and I'll see what i can do

[markboulton]

I would offer my services but I think perhaps it's been sorted already!

[markboulton]

By the way, can I just add I would love to see a Tech Forum here also!

[darrensetter]

I use Adobe Audition 3.0, which allows you to sample a clean section of the hum and then adjust the parameters of the 'correction' until you are happy with the result. Because it's rather old software, if you create an Adobe account you can download it in full from their website. I often use it on a low setting to remove noise from 78rpm records. It works well, but if the setting is too high it can leave the recording sounding rather 'empty'. I've not used it to remove hum, but it may be worth a try.

[brianfretwell]

I seem to remember Mark Ayers saying one of the main trouble with hum is the small changes in speed of old tape recorders over the length of the recording and that parameters would have to be changed to compensate. I imagine if not the hum level would change in various sections and might become more annoying than if constant. So do you adjust "on the fly" or do several passes and make a composite restoration from them?

Nothing in the world of restoration is easy, is it?

[John Smith]

There is a variable hum removal feature in RX4

[George D]

i agree with what is saying here.

When you get a hum, if its a particular frequency than that could perhaps be filtered out.

Many times people like to filter out pops, clicks, etc to remove the artifacts. Many times there is a tradeoff between sound quality. One may/may not notice it without a side by side, but normally you do lose the higher frequencies when general filtering is done.

The best way is to find a way of transferring it without the hum. Perhaps there is electric interference of feedback, or old equipment being used.

I have some tapes i would love to transfer, the problem is that I really dont currently have the right equipment to do it right.

[Ed Brown]

The BBC can afford access to pro hardware. Serious hardware, such as CEDAR, costs tens of thousands of dollars. But it does produce impressive results. Only hardware processing units do a professional job. Software solutions never completely cure either hiss or mains hum.

www.cedar-audio.com

If you want to experiment with Adobe Audition 3.0, probably the BEST software solution available, you can now download it (free of ccharge) here -

www.esotericsound.com/sfwr.htm

If you're interested in getting some free on-line pointers, start reading here -
www.rgbdigitalaudio.com/Primer.htm

This is their guide to Adobe Audition 3:
www.rgbdigitalaudio.com/Software%20Reviews/Audition_3_Review.htm

There're many enthusiasts out there, mainly fans of American old-time radio (search for 'OTR' on Google), who specialise in the esoteric mysteries of salvaging reel-to-reel, cassette and gramophone audio recordings. Here's 200,000 results on Google -

www.google.com/search?as_q=restoration+OTR+%22reel+to+reel%22&hl=en&btnG=Google+Search&lr=lang_en&as_ft=i&as_qdr=all&as_occt=any&as_dt=i&gws_rd=ssl