Playing with Noise Reduction And Other Effects

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ScottKelley
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Post by ScottKelley » September 29th, 2017, 12:50 pm

Greetings friends. Looking for some advise and/or direction on how to best reduce some background "hum" during recording. I am an Audacity novice and have been busy experimenting with the many settings and effects one can use on their audio recording. So here begins what will probably be a long-winded question.

Assuming I have a newly recorded audio, some direction given to me wast that I should immediately "normalize" the track to remove the DC offset and "normalize maximum amplitude" (mine is default set to -1.5 db). I guess my first question is, should normalizing the track be the first or last thing I do before saving? For instance, if I were to add more bass or change the noise reduction, should I do these changes before or after I normalize the track?

Second question is specifically in regards to Noise Reduction. I have a low hum when I record. My noise reduction default settings are - Noise reduction dB:12, Sensitivity: 0.00, Frequency smoothing bands:6. I have adjusted these a number of ways and have not found a setting that truly works for me. Can some folks share their Noise Reduction settings so I can try them out on my tracks?

Thanks in advance for your wisdom and guidance! :thumbs:
Scott Kelley

TriciaG
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Post by TriciaG » September 29th, 2017, 1:08 pm

You don't need to normalize (to -1.5 dB). Keep that box unchecked. It is a volume adjustment, which you don't need. ;)

However, your question about removing the DC offset before or after other things is still a good one. In my somewhat limited (but maybe more than others) experience with DC offset, it's best to do any recording of corrections first, then remove DC offset, then do whatever else you want to do for effects. That way all your recording clips are the same. Recording after removing offset means you have to remove offset on the clip you just recorded, too - so doing it all together saves steps.

And I think that doing noise removal, amplifying, whatever else should be done after removing the offset because those effects could be affected by the offset. Noise reduction might see the offset as noise, for example, which in removing it might give you weird results in the vocals themselves. Other effects might have other conflicts with DC offset.

For a low hum, if it's centered around one frequency (one tone rather than a whole bunch of them), Notch Filter can work better than noise removal. Find what your spike is (highlight part of the hum, go to Analyze/Plot Spectrum, and have the spectrum set for.. err... use the settings in this picture: http://ge.tt/5Mfm8jm2
In that picture, you can see a spike around 120 Hz. (It's a very quiet one since the spike goes to -72 dB).
So find your spike.
Then highlight your recording, go to Effects/Notch Filter, and put in your spike frequency. Experiment a bit with the Q number (I usually work with values of about 3 to 10).
Then you can highlight your hum and plot spectrum again to see what it did.

Hope this makes sense. I'm sure others will chime in. And if you like, you could upload a sample of your hum to the Tests folder for others to experiment with.

TriciaG
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Post by TriciaG » September 29th, 2017, 1:47 pm

P.S. If you have a really low-toned hum, in tones lower than your voice, a High Pass Filter may be effective. :)

knotyouraveragejo
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Post by knotyouraveragejo » September 29th, 2017, 2:54 pm

Good explanation of DC offset and why and when you should remove it in the wiki

http://wiki.librivox.org/index.php/Questions_and_Answers#Recording_is_Off-centre
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ScottKelley
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Post by ScottKelley » September 29th, 2017, 5:06 pm

Great feedback, thank you kindly for your time answering my questions. :D
Scott Kelley

lurcherlover
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Post by lurcherlover » September 30th, 2017, 12:41 am

Tricia has given good advice.

The hum could of course be mains hum (AC -alternating current). It would be 50 Hz in the UK and 60 Hz in the US. This usually means a ground loop - in other words - three pin earthed equipment making an earth loop which picks up hum. One way of stopping this is to make sure all your equipment - computer or recorder - pre-amp if used - mic etc - are all plugged into the same mains outlet. Either a double or triple socket or a mains splitter (i.e. a mains plug [extension] with three or four sockets).

The other aim would be to make your recordings so that no further processing is necessary which usually means using a close or very close mic and also maybe damping the refections (i.e. reverb) with duvets and blankets. You will not require noise reduction once this has been carried out. Keep as far away from the computer if you are using it as a recorder, so that fan noise and electrical interference is reduced.

Hope this helps.

Peter

PS Using DC offset is good if you have a plug in that does this, but normalisation will have no effect as far as I know. A small amount of DC offset won't be a problem though, and I would ignore it unless it gets much higher.
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ScottKelley
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Post by ScottKelley » September 30th, 2017, 4:28 am

:thumbs: :thumbs:
lurcherlover wrote:Tricia has given good advice.

The hum could of course be mains hum (AC -alternating current). It would be 50 Hz in the UK and 60 Hz in the US. This usually means a ground loop - in other words - three pin earthed equipment making an earth loop which picks up hum. One way of stopping this is to make sure all your equipment - computer or recorder - pre-amp if used - mic etc - are all plugged into the same mains outlet. Either a double or triple socket or a mains splitter (i.e. a mains plug [extension] with three or four sockets).

The other aim would be to make your recordings so that no further processing is necessary which usually means using a close or very close mic and also maybe damping the refections (i.e. reverb) with duvets and blankets. You will not require noise reduction once this has been carried out. Keep as far away from the computer if you are using it as a recorder, so that fan noise and electrical interference is reduced.

Hope this helps.

Peter

PS Using DC offset is good if you have a plug in that does this, but normalisation will have no effect as far as I know. A small amount of DC offset won't be a problem though, and I would ignore it unless it gets much higher.
Scott Kelley

TriciaG
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Post by TriciaG » September 30th, 2017, 5:47 am

PS Using DC offset is good if you have a plug in that does this, but normalisation will have no effect as far as I know.
The "Normalization" effect in Audacity contains the function to remove DC offset. Yes, it's a misnomer.

lurcherlover
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Post by lurcherlover » September 30th, 2017, 6:22 am

So it does! My mistake. I have never used Audacity for anything other than file conversion to mp3 - so have not explored that part. All my processing including DC offset is carried out in Reaper which has separate plug ins for each item, although when opened will do multiple processes as well.
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ScottKelley
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Post by ScottKelley » October 2nd, 2017, 1:16 pm

:thumbs: Much appreciated everyone!
Scott Kelley

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