Thanks Walt, Rob, Derek, Ed, Tim, Curt and anyone else I may have missed
who responded to my questions. It was a terrific learning experience for
me and gives me a lot to think about and experiment with for a while. I
hope to be able to do more of this in the future and hope that others were=
able to get something out of this dialogue. It really helps less
experienced people like me to have people who are so generous with their
time and expertise. I greatly appreciate it.
Thanks again,
Dana
At 09:36 PM 6/27/2006 -0400, you wrote:
>Posted by: "Dana Blackmer"
> >
> > Thanks, Walt. I have a few questions:
> >
> > I get the 80Hz noise in all my recordings. Is this "normal noise" for a
> > Portadisc and MKH 30/40? Also, is the "low shelf filter" you used to kn=
ock
> > it out equivalent to using an FFT filter in Adobe Audition?
> >
> > I have the same questions about the 18kHz noise.
>
>I think the filters are probably similar. The shelf filters are set for
>a target frequency, gain level plus or minus, and the sharpness of the
>cutoff in dB per octave. The result is cutting off all frequencies below
>or above the target depending on if it's the low or high shelf. The same
>filter could be used to introduce gain for the shelf, of course. They
>are also sometimes called cutoff filters.
>
>The noise at low frequencies does not appear to me to be due to the
>portadisc or MKH mics. It varies from none to very strong and it's
>primary source is distant man made sounds in my experience. Or distant
>storms, waterfalls, whatever. The lower the frequency the farther it
>carries so the higher frequencies of these sources have been filtered
>out. One of the sources at my house is a gas turbine power plant that's
>5 miles away. I can tell that one as it's run for peak electricity loads
>only so can detect when it's running or not. It's quite loud here in the
>low frequencies. Though only somewhat audible in general terms.
>
>With my MKH-110 SASS I can see even greater levels down into the
>infrasound. The MKH-110 has a design low frequency spec of 1Hz, though
>the portadisc limits out before that.
>
> > Concerning the distortion noise that shouldn't be there - can you descr=
ibe
> > it or tell me where it is on the sonogram? I didn't identify it and wou=
ld
> > like to be able to hear/see it as you did. If you worked on the file fr=
om
> > my original post (DawnChorus.mp3) the distortion may have occurred beca=
use
> > I may have inadvertently encoded the MS signal twice, using Audition's
> > Channel Mixer's "Mid-Side to L-R" pre-set. I later posted an original f=
ile
> > (www.danablackmer.com/AudioFiles/DawnChorusMS.wav) and an mp3 file
> > (www.danablackmer.com/AudioFiles/DawnChorusXY.mp3) that I know wasn't
> > double encoded.
>
>It's mixed throughout the sonogram in bands. The sound is sort of like
>water running down a fairly large drain. Also some calls have a sort of
>warble to them.
>
>The wav file is way too big for me to download through the modem, but I
>listened to the mp3 version. The distorted sound is gone. And in it's
>place is more insect sound, so that's probably what was messed up the most=
.
>
>Careful fiddling with the noise filter might allow some toning down of
>the insects, but it's tricky. Their frequencies are mixed through the
>frequencies of the calls you want. Insects can be a big problem here as
>the summer goes on. Really reduce how much reach you have for other sounds=
.
>
>Sometimes where you have a sharp band of insect sound and nothing else
>at that frequency you can use a notch filter or a very narrow parametric
>filter to take it down.
>
>With all filtering listen very carefully. And do sonograms. It's so easy
>to cut into what you want to keep. And any heavy filter application
>frequently results in new sounds produced by the filter. A light touch,
>sometimes applied more than once, generally works best.
>
>When first learning filtering do a awful lot of just playing with
>filters. Try all kinds of settings. When I first had to get serious
>about filtering for the GA frog CD, I spent over a month just playing
>with the files with filters before saving anything. What sounded good
>one day might sound poor the next.
>
>I also prefer to do critical filtering with headphones rather than
>speakers. Though I'm sure there are differences of opinion on that. My
>reasoning is I'm not having to deal with the room ambiance where I'm
>working on top of the site ambiance that I'm trying to preserve. And
>headphones generally color sound less than most speaker systems. Of
>course I do check out the results in speakers too.
>
> > You also said that you added and trained a denoise filter (Spark XL TC
> > Denoise) to decrease this distortion noise. Would this be similar to
> > Audition's Noise Reduction filter (a filter that works by capturing a
> noise
> > reduction profile from a segment of about 0.5-1" of noise-only sound an=
d
> > then using that to profile to reduce the noise in the entire recording)=
.
>
>Should be similar, though each filter differs slightly depending on how
>the programmer wrote it. I used a 500ms sample length, though it's
>settable down to just a few ms. The noise reduction filter I use has a
>audition function where you can listen to the sounds that will be
>removed as you play the piece. Helps if you are trying to preserve some
>sound. I sampled until the green frog calls would be removed minimally
>and there was the least change in the sonogram. The sonogram just looked
>cleaner.
>
>Walt
>
>
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