Hi,
Ive tried a few methods, are you talking about "noise floor" from the =
mic or preamp? or general noise pollution?
For Pollution,
Use baudline for a 65K FFT flat EQ against a known noise source, you can ch=
oose a section in the recording and EQ against that (if your not running li=
nux, virtualbox + ubuntu will work in windows or mac os x to get you going)=
.
Despite such a tool, very careful EQ such as the example Rob provided I bel=
ieve to be the best method, removing noise to preserve just the signal ster=
ilizes the acoustic portrait you took during the recording. If capture of t=
he bird vocalization is paramount maybe switching to a narrow beam shotgun =
mic, or a parabolic dish? and not the NT1A's?
Just a thought, I face the same problem myself - I need a magic acoustic er=
aser for traffic noise.
Then again the obvious solution is take a trip where there is less noise po=
llution in the first place - akin to moving your telescope to a dark(er) si=
te.
BIAS sound soap etc is one tool, never really had much joy with it myself. =
The other is removing the noise via e.g FFT preserving the signal, and addi=
ng your own background noise recorded earlier (providing thats noise free..=
.) - which has been discussed here before I think...
If its purely preamp noise, different recorder is needed that has a EIN low=
er than the noise in your mic (calculated from sensitivity + self noise and=
max spl see the rane site for a description of that..) - or if its mic noi=
se (from the NT1A????) - then a higher sensitivity is needed, or to the ext=
reme a directional mic array with many elements.
You can also increase sensitivity in specific bands by adding mechanical "E=
Q" around the mic or specially constructed resonator at the specific freque=
ncy of interest. Ive recently designed a system that boosts 4 Khz and 8 Khz=
by 10 and 8 dB respectively, when the "bump" is removed via EQ at those fr=
equencies the result is very quiet. (The self noise of the mic remains the =
same, just the signal in those regions is boosted by the mechanical coupler=
) - Some times we do the same, by placing a hand behind our ear to listen t=
o quiet sounds...
Another system Ive recently investigated is based on a paper from Neumann i=
ts a log spiral boundary array, this is a log spiral with an electret in th=
e center - it will give around +6dB 'bump' from 1 to 10+Khz, must be quite =
effective at reducing the noise due to the increase in signal.
Kind Regards,
Mike.
--- In "jmccubbinmd" <mccubbin.astronomy@=
...> wrote:
>
> --- In Rob Danielson <type@> wrote:
> > Hi JM--
> > Fun analogy to think about. Are there some astrophotographers who
> > insist they are documenting "space" opposed to only identifiable
> > objects? "Noise" is a very rich construction when I think of it as an
> > overlap between perceptual and technical limitations.
> >
> > Here's a QuickTime movie experiment I did with your recording and
> > noise reduction examples:
> > http://tinyurl.com/okwpc6
> >
> > If you have trouble viewing it, I can make an mp3.
> >
> > Rob D.
>
> Noise in an astrophoto image translates into grain. The great thing abou=
t digial imaging in astrophotography is that we use very crude cameras in c=
omparison to say, my Canon 5D MkII. I basically capture a raw frame with n=
o processing and no "raw import" utility. It has hot pixels all over it. =
Some of my exposure times are measured in hours. But that's off topic.
>
> I hastily processed that audio, and I'm sure there are artifacts in it. =
What I would like to know is what are the typical processing tricks people =
use to get the noise out of the audio. This is going to become more and mo=
re essential as I try to get the really quiet things around. In the earlie=
r audio of that 18 minute sequence, I can hear mosquito's buzzing around th=
e NT1-A's. So I'm going to have to learn a few new tricks.
>
> I'll work on that audio with Logic, which tends to have cleaner tools in =
my opinion. Then I'll see what I can do with it.
>
|