Noise in classroom recording

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Noise in classroom recording

Permanent link to this post Posted by Alonshow » Thu Jun 04, 2015 3:40 pm

I'm a novice teacher and I'm recording my lessons to improve my teaching technique. My recordings have a lot of noise that comes from several sources: Air conditioning, chair creaks, traffic, etc.

The method that has worked best so far has been using notch filtering when I can identify limited frequency noises and then using noise reduction. This does help, but the results are still quite poor.

My knowledge of sound editing is almost none. Anyway, after a bit of googling I've come to the conclusion that this problem is called vocal isolation. If I'm getting it right, there is no real solution for this, just some tricks that can help a bit, so I guess that's what I'm looking for.

I have checked Audacity's tutorial on Vocal Removal and Isolation, but this doesn't seem helpful for me because my recordings are mono and that tutorial talks about stereo tracks.

So, can you recommend some method, plug in or tool that can help?

I attach a sample:
Voice and noise.wav
(916.73 KiB) Downloaded 82 times


Audacity 2.1.0
Windows 7
Exe installer
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Re: Noise in classroom recording

Permanent link to this post Posted by DVDdoug » Thu Jun 04, 2015 4:16 pm

There's probably nothing more you can do. The problem is that most "natural" noises cover the same basic frequency range as the human voice. If a noise has a certain frequency pitch (like power-line hum,etc) it can usually be filtered-out. IN fact, it may help to use a high-pass filter at about 200Hz or so to filter-out any low-frequency noise.

The Noise Reduction filter can also work when you have a small-constant background noise like tape hiss, but if the noise is bad the software can't distinguish the signal from the noise and usually, "The cure is worse than the disease".

In the future, your best bet is to use a lapel mic or a podium mic for a strong signal-to-noise ratio. If that's not possible, a try directional mic as close as possible to you. You're never going to get "studio quality" in a classroom but if your voice can dominate the sounds hitting the microphone you should be able to get acceptable results.
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Re: Noise in classroom recording

Permanent link to this post Posted by kozikowski » Thu Jun 04, 2015 8:51 pm

if your voice can dominate the sounds hitting the microphone you should be able to get acceptable results.

What he said.

Image

Nobody yet has gotten good recordings from across the room or even on a chair somewhere on the stage.

People still do this for a reason.

Image

Anyway, there are a number of techniques you can use to record as long as you never need to submit to NBC, NPR or the BBC.

What are you using now before I go off in all directions?

Koz
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Re: Noise in classroom recording

Permanent link to this post Posted by kozikowski » Thu Jun 04, 2015 9:14 pm

Would this work for you (attached). I need to get the part numbers and purchase info.

Koz
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2015-06-04SoundTest.mp3
(1.79 MiB) Downloaded 66 times
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Re: Noise in classroom recording

Permanent link to this post Posted by kozikowski » Fri Jun 05, 2015 3:32 am

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Re: Noise in classroom recording

Permanent link to this post Posted by Alonshow » Fri Jun 05, 2015 5:23 pm

Thank you for the advice. I guess I already have the best I can get in this situation. It's not too bad, actually. Dealing with the noise removal process and the remaining noise is time consuming and annoying, but I'll deal with that.

Using a lapel mic wouldn't help much. These are very interactive English lessons and the voices of my students are as important as mine. For the same reason, the directional mic doesn't seem to be helpful in this situation.

Regarding the USB recorder, it looks cool, but I have a recorder already, it doesn't look like it's gonna make any improvement either.
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Re: Noise in classroom recording

Permanent link to this post Posted by kozikowski » Fri Jun 05, 2015 6:26 pm

Recording a classroom well with student interaction is a graduate course in professional sound recording. Now you know why.

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Re: Noise in classroom recording

Permanent link to this post Posted by tracy18 » Wed Nov 29, 2017 7:52 am

I am a teacher too, grappling with changing Technology to improve my teaching skills. And I definitely understand your trouble of recording your classroom lessons in real time. I prefer recording my lessons in isolation as a practice before I actually try out the lessons in the classroom.
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Re: Noise in classroom recording

Permanent link to this post Posted by kozikowski » Wed Nov 29, 2017 11:21 am

I prefer recording my lessons in isolation as a practice before I actually try out the lessons in the classroom.

That will give you your lecture clean. How do you deal with the student questions or responses?

And yes, there is a time-honored tradition of "Studio Recording" the work to get a clean presentation when recording in the field fails. That puts you in the Post Production situation. "Post" takes at least five times the length of the finished show.

I know "Studio" is a bad word, but just recording the presentation in a better room can work miracles.
Dealing with the noise removal process and the remaining noise is time consuming and annoying

There are ways to solve this problem, too. You issue one of those tiny, self-contained microphones to each student, collect them at the end of the lecture and mix them into a finished show.

You have an actively hostile recording environment. I know of no quick and easy solution.

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Re: Noise in classroom recording

Permanent link to this post Posted by university.details » Tue Dec 12, 2017 6:08 am

Have you tried Audacity's default features for removing background noise from your audio recordings?

Personal notes, or a recorded interview, should be fine with the ambient background audio left intact.

To filter out the ambient background noise, you’ll need to find a section of audio where it can be heard alone, isolated. This might involve splitting a stereo track to two mono tracks (via the down-arrow on the Track Control Panel, and selecting Split Stereo Track).

Once you’ve found the audio — which Audacity will use as an example — you should select it with the mouse. Make sure the Selection tool is selected, then left-click and drag the section of background, ambient audio.

This audio selection will be used by the Noise Reduction feature in Audacity to find similar background ambient, and remove it from the track(s). Not only is it pretty clever, the end results are almost always superb.

With the audio selected (it will be highlighted in blue), open the Effects > Noise Reduction feature.

Once this is done, preview the results. If you’re happy with them, hit File > Save to retain the change.

Hope that helps.

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