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boosting sound on home movie

 
 
fruitbat
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      01-01-2009
I have a number of short home movies that are in .AVI format.
The sound is there but is too low in volume. The video part is fine.

What is a simple way to convert or recode or otherwise that will keep the
existing video but make the sound louder?



 
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Paul
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      01-01-2009
fruitbat wrote:
> I have a number of short home movies that are in .AVI format.
> The sound is there but is too low in volume. The video part is fine.
>
> What is a simple way to convert or recode or otherwise that will keep the
> existing video but make the sound louder?
>


There is a function that does the right kind of thing, in Audacity
(audacity.sourceforge.net). The function is called "Normalize", and
what it does, is scan a sound track, for the strongest sound, and
make it full level, and all other sounds are relative to that
volume level. That ensures that the sound track doesn't clip (snip
the heads off the sine waves). So you'd want a video application
that has the ability to "Normalize" the sound track. It is also
possible to normalize to an arbitrary sound level, so instead of
bringing it up to 0 dBm, bring it up to -10dBm etc.

The other kind of effect, would be something like companding. That
is what they use, to make commercials on TV so annoying. It sounds
like everyone is yelling all the time.

http://en.wikipedia.org/wiki/Companding

Another issue for you, is if the sound is really low level now, the
sound samples may not have a lot of bits of resolution. You may
find, when the signal is amplified, using something like
normalize, that the sound track really sucks. There is no
cure for that, except to record the sound at a decent level
to begin with. For recording devices that have a vu meter,
the indicator is telling you whether you're close to getting
the right level or not. If the needle on the vu meter isn't moving
off the bottom peg, you don't have enough level. You don't want
the recorded sound to be so loud, that the needle goes "into the red",
because that means the original recording will be clipped (and
that would be pretty hard to fix by comparison).

I've only played a bit with video, and I've noticed that sound
is handled poorly, and the output always seems to be on the
low side. So this kind of thing is probably a common condition.
There should be some provision to fix it, in a video editing
application. (I just took a look in Windows Movie Maker, and
if you right click on the audio track in the clip on the timeline,
you can set the volume there. I have a clip loaded right now
from my webcam, and when I amplify the sound track, I get lots
of juicy background noise to spoil the result... You can't win.)

Audacity has a bunch of filtering functions, which I've experimented
with in the past. Audacity has standard effects, and some optional
effects (why they aren't in the tool already, is a puzzle). I added
the "notch" effect, which can be used to try to knock out "hum"
from a recording. But for some kinds of background noise, the noise
is too random for tools of that type. Just as an experiment, I tried
to fix a poster's sound track, but was unable to get any improvement,
even after applying the notch 30 times in a row, applied to different
noise frequencies.

Paul
 
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Neil Green
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      01-01-2009

"fruitbat" <(E-Mail Removed)> wrote in message
news:495c7649$(E-Mail Removed)...
>I have a number of short home movies that are in .AVI
>format.
> The sound is there but is too low in volume. The
> video part is fine.
>
> What is a simple way to convert or recode or
> otherwise that will keep the existing video but make
> the sound louder?


The bottom line is that a poor recording is a poor
recording, and no amount of reworking will improve it
more than marginally.
You could use some free tools to achieve what you want
or close to it, or something like Sony Vegas which
will do what you want more easily but I'm not sure of
the cost.
Virtual Dub will demux (separate the audio and video
tracks), you can then use something like Audacity (MP3
Gain if you convert the audio to MP3) to amplify and
clean up the audio track then remux (combine the audio
and video) again using Virtual Dub.
Sony Vegas or similar is by far the easiest route, and
probably the most effective, but the alternative is
free.


 
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Jeff Strickland
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      01-02-2009

"fruitbat" <(E-Mail Removed)> wrote in message
news:495c7649$(E-Mail Removed)...
>I have a number of short home movies that are in .AVI format.
> The sound is there but is too low in volume. The video part is fine.
>
> What is a simple way to convert or recode or otherwise that will keep the
> existing video but make the sound louder?
>
>
>


It is _possible_ (actually, very likely) that there are two volume controls,
one for the system (the control is by the clock) and the other for the
playback device. You can have one control set high and the other set low,
and the problem you are asking about will result.

If the System Sounds are low, then the confirmation ding that comes from
acknowledging a system activity will be low as well as the playback sounds.
Some playback applications will use the system sound setting, and an
adjustment from the app will adjust the dings and chimes of the system as
the video is adjusted. Other apps use a separate adjustment for the app and
the system.

Of course, the mic on your camera also has a volume control, and if it
recorded a scene under muted conditions, the playback will be muted too. If
you can connect your camera to the TV and the sound is okay, then I think
your issue is that the playback application in your computer, or the system
volume settings.



 
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