removing loud audio hum from voice recording
OhioGuy
record a ~45 minute audio interview to use as my source material. Now
that I get around to reviewing it, it sounds ok for the first second or
two, then an audio hum overwhelms the audio to the point where I can
just barely make out the speaking, but not well enough to get anything
out of it, no matter how long I spend straining. I originally thought
this was an issue with the audio out headphone jack on the Sansa
Express, but the problem persists even after I transfer the file to my PC.
The Sansa Express records Microsoft ADPCM, 89 kbps bitrate, 4 bit
sample size, in mono, and a sample rate of 22 kHz. It appears to be
saved in a *.wav package.
Anyway, when I play the file with VLC Media Player, and I choose the
oscilloscope visualization, it shows two distinct wave patterns. I'm
wondering if one of them is the audio hum, and if there might be some
way to use software to edit the adpcm file so that the audio hum is
removed, or at least lessened, and I can then listen to the recording
and use it for my article.
Anyone have experience with something like this? Thanks!
OhioGuy
> frequency (like 60hz). You may lose a little of the content but the
> hum will be gone.
>
Now I'm not sure it is a specific frequency. I looked at the
waveform, and it looks like little 'spikes' going down into negative
territory - about 100 per second. However, when I play it through my
stereo and use the graphic equalizer, a bit more of the noise disappears
when I move the upper frequency sliders down. When I zoom in even more
to the wave, I see that the noise is a pulse that lasts 3 ten
thousandths of a second, and begins every hundredth of a second. It
looks like a v, with the bottom of the trough going down to about -.18
from zero.
No matter what I do, though, it appears that since the hum is 2 to 3
times as loud as the people speaking, I am having a really tough time
making out what they say. The annoying thing is that the Sansa Express
recorder will not duplicate this problem - it appears that the thing
only had this problem when I was sitting in their office near the
computer and a bunch of other electrical equipment. Hence, I'm thinking
it might have been RF interference of some kind. Every recording I do
now is quite clear.
I used Audacity to apply a high pass filter, then tried a low pass
filter. No help.
I think next time I'm just going to take a backup recorder, and have
two of them running, just in case.