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Sound editor - how to adjust sound volume

I recorded a 2 1/2 hour interview (video/audio .avi file).  I messed something up in my setup so that one of the people was recorded at a very low volume.  I suspect there is some editing software that will allow me to define parameters (decibals?) so that any sound below certain decibals can automatically be amplified (i.e. amplify the low volume person) or reduce the volume of the normal volume speaker to be low to match the low volume person, and then maybe amplify the entire recording afterwards?

How can I recover from this problem so that I can amplify the low volume recording of the speaker?  Unfortunately the both speakers were recorded to the same audio stream.

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1 Solution
It needs compression.

I haven't tried Audacity's compressor but i think it's a good place to start (unless you have a hardware compressor).



Nice thing about digital audio is that it can be done non-destructively.   Make a copy before you experiment with this method.
Hello Asked by: SAbboushi

If your recording is an MP3, then you will also need to install the MP3 plugin.  Download and install the Audacity 2.0.2 from here:
then follow the links to the "LAME MP3 encoder" just below that.
Along with the instructions you will see a link to the developer page:
Scroll down beyond the advertising links and look for "Lame_v3.99.3_for_Windows.exe".
Download and install that.  I usually choose the plugin sub-folder of the Audacity program folder to install this rather than it's own "Lame For Windows" program file, but it's not important and will still work wherever you install it.

The instruction manual for Audacity is here:
This runs you through the basics:

It's actually quite simple, but here are some tips:

Edit Menu > Preferences.  They are detailed here:

Make sure that the Lame Encoder for MP3s has been located:

Make sure it shows the Metadata (MP3 Tag) editor when you export after editing:

So it's pretty easy.  File > Open or File > Import > browse to your audio file and select it.
Wait until it opens and shows as the wave form.
Select a portion of the audio to apply an effect to by scrolling over it, or just leave it as it is to apply the effect to all the audio.
Effects menu > choose the effect > make adjustments in the dialog > Preview > Apply.
Play the audio back and listen.
Edit > Undo if not happy.
File > Export > choose MP3 from the drop down list of file types (eg. MP3) > click Options > set the quality.
Enter any tags in the metadata editor that should show:
Close Audacity when done, and in your case there really is no need to save a project.

I actually prefer the compressor effect by Kjaerhus, as shown here:
but it's unavailable from there.  Because more recent versions of Audacity are able to show some effects that are designed with nice realistic graphic interfaces, you get a much easier hands-on experience with one like this.

I see that this page has a combined installer for all the Kjaerhus "Classic" VST effects
but I don't know the version numbers.  These effects are just a DLL file for each, and simply need to be dropped into the "plugins" or plugins\VST" folder in the program folder where Audacity is installed.

If you prefer just to have the Compressor, then I will look and see if I have a download link when I get home from work.

If you are just copying an effect DLL into the plugins folder, then you need to tell Audacity to find it.  After you add the new effect DLL you need to go back to the preferences dialog > "effects" and tick the box to rescan for plugins the next time Audacity is started, and it will find the effect.

I hope this helps.
SAbboushiAuthor Commented:
tailoreddigital - thanks -- I tried compression and messing around with the settings, but no joy.  

BillDL - thanks for all the info.  Much appreciated.  Yes, generally working with mp3 files.  Spent a couple of hours, but I am very ignorant about sound and diagnosing what needs to be done.

I have attached a clip (few seconds) from another recording I am working on right now with similar problem - if anyone has the time to check it out and tell me what effects/settings help.  I tried amplifying the soft part, which helped a bit, but background noise shot up.

Thanks for any help--
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Thank you for the sample Sam.  I will mess around with it and see what seems to work best.
Hi Sam

I am really struggling with this one.  The recorded level of the male voice asking a question in the sample is so low that it has been impossible for me to boost it up to an audible level without the voice being swamped by the hiss and other background noise that has also been boosted.  You can really only amplify audio up to a certain point where it begins to "clip" (distort), and when you end up distorting an already annoying background noise as well as the audio you want to boost, it makes an intolerable racket.

It is usually possible to suppress certain frequencies so as to reduce background noise, and then boost the audio content that remains, but the problem with your audio sample is that the background noise is almost at the same level as the almost inaudible male voice, and when I suppress specific frequency ranges it also affects the voice, thus undoing any beneficial steps.  Getting the noise profile to try and automate this has been impossible for me.

Here's how your sample audio clip looks as a wave form in Audacity:
Dramatic differences in levelsPersonally I think this would be a job for a professional audio engineer or a forensic audio expert, both of which might be expensive.

Perhaps another expert here might be able to get a reasonable result where I have been unable to.  Sorry.
SAbboushiAuthor Commented:
Thanks BillDL - I really appreciate you having taken the time to try.  I accept your assessment that the answer to my question is:

this would be a job for a professional audio engineer or a forensic audio expert

With Regards-
Ah you posted a sample,  

using a combination of amplification and noise reduction, you can improve this,  see attached (it's a WAV)
SAbboushiAuthor Commented:
Thanks -- it sounds like both speakers are slightly amplified, but I still can not really hear male speaker: not sure ratio of loudness of speakers has changed noticeably... thanks for efforts.
Thank you Sam.

Just for your info, the screenshot I attached earlier is of the wave form after trying to boost the quiet content to an acceptable level through noise reduction, amplification, and a few other effects.  Even though you can start to see some amplitude in the interviewer's audio section (ie. wiggly waves now becoming visible) that is full of background noise too, and trying to remove that sets the wiggly line back to almost flat.

It just occurred to me that perhaps your main aim here is not so much permanently improving the interview to preserve it for future reference or use in some kind of publication, but simply to listen to it in order that the questions and answers could be transcribed into a printed article.

If you simply need to be able to hear the interviewer asking, for example "It would help if you could answer that question" as is just audible in the sample clip, then what you could do to help you transcribe the content is to selectively:

1. Reduce the loudness of the interviewee
2. Boost the interviewer.


1. Dramatically reduce the loudness of the interviewee
2. Boost all of the audio (ie. suppressed interviewee and previously unaltered interviewer).

That would allow you to turn the speaker volume up pretty high and hear what the interviewer was asking (although it would still contain a lot of background noise), but it wouldn't suddenly blast the roof off each time the interviewee answered.

It would take a fair amount of time doing this manually with 150 minutes of audio, but the good thing is that there is such a massive difference in loudness (interviewer vs interviewee) immediately visible to you in the wave form of an audio editor like Audacity, that you could work your way through the whole lot and quite effortlessly select each loud section and apply a "minus amplification" until the wave form at those points is squashed right down almost to that of the quiet parts.  Having done that to the entire audio file, you could then amplify the whole lot by the same amount.  That way you would be able to hear the interviewer to transcribe the questions without having to reach for the volume each time the questions are answered.

If your aim is to actually use this audio for some other purposes, such as playback in a lecture, in some other multimedia publication, for evidential purposes, etc, then as I stated in my earlier comment you would need an audio engineer or forensics expert with some fine equipment and audio filters.  What we see the gothic Abbey or techno-babble McGee doing with audio files on NCIS or the wondrous miracles performed by the investigators on CSI isn't always possible in real life.
SAbboushiAuthor Commented:
1. Reduce the loudness of the interviewee
2. Boost the interviewer.


1. Dramatically reduce the loudness of the interviewee
2. Boost all of the audio (ie. suppressed interviewee and previously unaltered interviewer).

Transcript would be second best and certainly better than nothing.  I tried to do what you suggested before posting, but my lack of knowledge (both about sound and about audacity) were obstacles, hence my post.  If you can  do what you propose to the clip and then share the step-by-step of how you did it, that would be so helpful.
I'll do this and attach the mp3 when I get home from work.  I'm at a PC with no sound and unable to install Audacity, but as a general guide in the meantime you could experiment yourself like this:

1. Open the MP3 in Audacity
2. If not already selected, select the tool that shows as the "I" beam up in the toolbar.  The one directly beneath the "analyze" menu in this screenshot:
3. Click right at the start of the loud part of the wave form and scroll to the end of it.
4. Effects menu > Amplify:
Move the slider to the left (minus) a fair amount and click OK.
5. You will get an immediate idea of the loudness by the amplitude of the wave form.  Try to get it really low but so that you can still see the waves and peaks.  Listen to it to ensure that it is really quiet.  Edit > Undo amplify (Ctrl + Z) if you need to change the slider and reapply.
6. Now click right across in the left of the track in the grey area where it shows a 10 in this screenshot.  http://manual.audacityteam.org/o/index.html#reference  That selects the entire track.
7. Effects menu > Amplify.
8. This time tick the box "allow clipping".  If you don't tick that you will probably only be able to move the slider slightly to the right.  Experiment with this, using the undo each time until you get it as good a compromise between audible and horribly distorted.  The wave form will only be a reasonable approximation of how useful the results are, because a lot of the loudness will be background noise with what were the quieter bits before.

I'll post something later.
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