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How to Prevent Echo During Noise Reduction

Nov 18, 2013 10:07 PM

Tags: #echo #noise #removal #reduction #prevention

I had a dickens of the time trying to find out how to reduce the echo that is left after background noise is removed. However, I didn't give up and after playing with some of the settings, I believe I've figured it out! I'm using Adobe Audition CC (6.0). You'll want to follow the steps below as your method of noise reduction, not after the fact. So we're preventing the echo during noise removal, not getting rid of it...if that makes sense. So start with your original audio with the noise, then...

 

  1. Perform the usual procedures of selecting the background noise and sampling it (SHIFT + P)
  2. Select all the audio (CTRL + A)
  3. Get ready to apply noise reduction: Effects > Noise Reduction/Restoration > Noise Reduction (process) OR CTRL + SHIFT + P
  4. In the window that appears, I played around with three settings (see image below):
    • Noise Reduction slider (85%)
    • Reduce by slider (about 40 dB)
    • Under the "Advanced" section (you may have to click on the little triangle/arrow to expand it), the Spectral Decay Rate (10%). It was this final setting that made a HUGE difference!
  5. Put the audio on loop if it's a short clip and click the play button to hear a sampling of the noise reduction applied.
  6. Adjust the three settings mentioned above until you have the desired effect.
  7. Click "Apply".

 

I hope that helps!!

 

noise_reduction_remove_echo.PNG

 
Replies
  • Currently Being Moderated
    Nov 18, 2013 11:42 PM   in reply to ArialBurnz

    May I make a suggestion?  Although you're experiments were useful, trying to find a one size fits all "one pass" solution probably won't yield the best results.  Basically if you can hear NR artifacts (the echoey quality you refer to) at any point, you've done too much noise reduction in one go.

     

    Generally, you're better off doing 3 or 4 passes of very light noise reduction, grabbing a new noise sample each time.  For most "normal" noise, it can also be very worthwhile to increase the FFT size (on the advanced menu) a preset or so before grabbing each of those sequential noise samples.

     
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  • SteveG(AudioMasters)
    5,602 posts
    Oct 26, 2006
    Currently Being Moderated
    Nov 19, 2013 1:56 AM   in reply to Bob Howes

    In fact, you generally don't want to take off very much at all at FFT4096. You can get way better results from much higher settings, almost regardless of what sort of noise it is. Since the FFT size essentially determines the window width, lower settings are really only much use on low frequency noise, and they are the ones responsible for most of the strange sounds you hear in the rest of the frequency range. The reason for this is that you get many samples of higher frequency sound within the wider window, and the processing simply can't do anything with it. The higher FFT sizes mean that signal slices with HF in get dealt with much more accurately, hence less 'bubbly' noise. The downside of course is that processing takes significantly longer.

     

    So thanks for posting, ArialBurnz, but I'm afraid you've only just scraped the surface! Bob's method of doing multiple passes at different rates is definitely the way to do with Audition's NR, but you will always get better results in terms of remaining artefacts from higher FFT settings.

     
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  • SteveG(AudioMasters)
    5,602 posts
    Oct 26, 2006
    Currently Being Moderated
    Nov 19, 2013 11:53 AM   in reply to ArialBurnz

    ArialBurnz wrote:

     

    I had a dickens of the time trying to find out how to reduce the echo that is left after background noise is removed.

    Ah, well if you'd have asked us in the first place, we'd have told you immediately what to do! And it's not overkill - it doesn't take long and works miles better.

     
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  • SteveG(AudioMasters)
    5,602 posts
    Oct 26, 2006
    Currently Being Moderated
    Nov 19, 2013 4:43 PM   in reply to ArialBurnz

    Right, if you want a quick fix then before you take your noise sample, alter the FFT setting to the highest it will go. Then take your noise sample. Now you will find that you have a lot more lattitude to play with before strange noises get in the way. The other thing that sometimes helps (although I don't think it will in your example above) is to shape the amount of NR - that's what the blue line is for. You can add points to it and drag it up and down. This will give you the opportunity to listen to where the most obtrusive noise is, and shape the response so that it attenuates more of that, and less where it isn't so significant. This also reduces the chances of artefact noise just to the band where you're taking most out. Because you've reduced the artefact noise anyway, you'll get away with a higher (longer) spectral decay rate, which should reduce any abrupt cut-offs - more important with speech than anything else.

     

    The other thing that's sometimes worth checking is the 'output noise only' box during preview - this will rapidly show you when you're removing wanted signal as well as noise - but remember to remove the check before doing your actual processing - or you end up with only noise!

     

    And also remember Bob's advice - take at least two swipes at it, using the highest FFT setting for one, and a lower one for the other. It doesn't matter which order you do them in, but you'll have to take a separate noise sample for each, because they are FFT-size specific.

     
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  • Currently Being Moderated
    Nov 20, 2013 8:40 AM   in reply to SteveG(AudioMasters)

    And when you take a couple of goes at it don't use the full default Reduce By setting of 40dB. That is too much at a time. Try only about 15 - 20dB or less at a time.

     
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