>
>At 01:20 AM 6/22/2004 -0400, Scott wrote:
>
>>I am going to try this one more time. I went through all 13000+ messages
>>in the archives and could not find anything on basic filtering. I have
>>seen comments where one contributor stated that every recording he does
>>goes through an FFT filter. I know that not everyone here uses CoolEdit
>>but I am sure that the principles are the same. When one makes
>>recordings that catch background car noises, wind buffeting, operational
>>machinery, or water, what is the approach that you would use in
>>filtering the recording? Are there settings that one would consider
>>standard in editing any outdoor recording? If there is a good reference
>>somewhere on this, I would really appreciate knowing it. I don't have a
>>manual for my version of Pro 2.1 and I don't have an acoustic background.
>
>Dear Scott:
>
>I have written explanations of how I use Cool Edit's FFT filters over the=
>years (see copy of message #376 below). The details were in a followup,
>Msg. # 394 et seq., e.g. #489, #497, #867 for tips. I have written and
>offered a short computer course, with examples files, exact settings and
>key-by-key instructions for free to anyone who wants to try it, just to
>get to know how to edit any natural recording to produce the best sound of=
>a single source from what you happened to get. It included morphing
>filter designs. I had one taker who took the sound files, spectrum
>examples and course text and never got back to me, so I have no idea if
>interest was lost or it was all just too detailed or incomprehensible for=
>him. It was two years and two computers ago, and I would have to hunt for=
>it, now. It is about 20 megs in size, if I recall.
>
>I suggest you not try to assimilate this post all now, but print it out,
>and use it with actual field recordings as the need occurs.
>
>First, I must say, your question I think cannot be answered as such,
>because I do not know to what purpose your final recordings will be
>put. For example, Lang Elliott and Bernie Krause usually want to recreate=
>sound-scapes for the listener. In contrast, I want to give the listener
>brief sound-bytes that quickly allow them to learn species identity for my=
>bird-ID product, EnjoyBirds - Q.V.
>http://www.enjoybirds.com/index_files/page0006.htm So I deliberately cut
>out other ambient sounds and brutally chop out quiet places to present the=
>most sound for the least disk space.
>
>Where the purpose is to surround the listener with realistic sounds, the
>use of any FFT filters is usually avoided. Any notch or band filtered out=
>makes the overall recording sound harsh, muffled or hollow, depending on
>the band you have eliminated. But where three birds are singing
>simultaneously, and their frequency usage bands are exclusive, the FFT
>filters produce three separate files, one of each species, and it is in
>that mode I have some experience.
>
>Usually there are these steps in reducing a raw recording to a usable
>species example, IF THAT IS YOUR PURPOSE. I usually record from two
>angled shotgun mics at once, so initially I decide which was pointed at
>the singer most accurately, or which had the LEAST annoying extraneous
>sound in the channel, and convert that single channel to a mono file for
>editing. Often low level recordings are also normalized to 85% of max at=
>this time. DO THIS FIRST, before editing. If you thought the b.g. noises
>were nearly acceptable initially, this step usually makes them so loud you=
>just feel you need to do some editing. This is the order:
>
>1. Scan the whole recording for the clearest sound examples, with least
>overlap from other noise sounds.
>2. Using click-drag select, and the <delete> key, remove the loudest
>interruptions and trim the file to begin to produce a final cut. Save it=
>as a new file name at each stage. If I have a recording of an American
>Robin, the original raw cuts would be saved in a project-specific
>directory named \Pittsburgh2001 or some such, and would be named as
>TURMIG00.wav, TURMIG10.wav, TURMIG20.wav, etc.and I would save the first=
>one edited as TURMIG01.wav. Say it produced three songs, with some car
>noise and roosters in the b.g.
>3. I remove any impulse noise BEFORE band filtering, which would spread
>out and ruin any sharp clicks or pops.
>4. Set in spectral mode, I try to get a handle on the noise frequency
>structure, and on that of my desired species. This typically involves
>looking more closely at the lower bands, using Alt-UPARROW to expand the
>vertical spectral scale.
>
>In this example, the robin sound never falls below 800 Hz and the car
>overlaps a bit from as low as the mic recorded - say 30 - 50 Hz, up
>through 1200 or more Hz. So I know this will be a compromise. I also
>know that any FFT filter curves I make need gradual edges, NEVER sharp
>domain walls. The latter cause distress among listeners of all kinds. In=
>fact, the final sound file should have the background sounds as nearly
>flat across the spectrum as possible for a listener to judge it as being
>acceptably natural. So my goal, given that the car and the birds overlap=
>in the 600 to 1200 Hz region, is not to cut OUT the car, but to reduce it=
>so it is the same loudness and other background sounds average in the
>range of the robin songs as well. Put another way, if the robin was not
>singing, all the sounds should average out at about the same loudness from=
>bass to treble. If the b.g. is structured on this plan, it will minimize=
>user questions such as:" What is that hiss?" or "What caused that roar?"
>
>5. I set and save the file to a new name, e.g. TURMIG11.wav, and begin the=
>FFT trials.
>I have a starting filter: at the top the Log box is checked; on the middle=
>right the top box says 40 db, the lower on -40 db.
>The line is in the middle stretching from 0 dB to 0 dB. This flat filter=
>does nothing to the sound. It is the canvas, if you will, on which the
>best filter line will soon be drawn, by repeated trial and error. My
>starting filter looks like the picture saved to my web site:
>http://www.enjoybirds.com/HowItWorks/exFFT01.jpg
>
>
>
>I drag the lowest point down to about -30 and drop it. When you put the
>cursor on the line anywhere and press and hold the left button, you set a=
>node on the curve. You can move it up or down, to cause gain or loss at
>that point in the curve, which becomes a "knee". Where you have loud b.g.=
>noise throughout the recording, you drag the curve down, making as few new=
>nodes as you need. Typically I drag 60 Hz down part way as low as the
>bottom, and 400 Hz part of that way, making a gradual curve that increases=
>the bass loss as the freq. point goes down. But this will vary with each=
>recording. The rule is make the b.g. in final recording sound flat, and
>only drag a point as low as it needs, avoiding vertical parts for the
>curve. Also: Do it all with one complex curve. doing successive filter
>makes it sound lousy very soon. To delete an extra knee, drag it off the=
>edge of the window (that one took two weeks to figure out).
>
>Do not be tempted to raise any part of the line above 0 dB, as the ensuing=
>sounds will very likely exceed the maximum signal level for the file
>without warning and the result will be permanently ruined. Keep clicking=
>the [Preview] button {in the middle right} to hear the result. It will
>all sound almost the same until you do it a few hundred times. When you
>like it, click [Ok] and look at the spectrum that results. Almost
>there? Press Ctrl-Z to undo the filter, then [F2] to redo it, modify the=
>position of a few nodes again, and try [Ok] again. Play with the file for=
>as long as it takes to fulfill your design goals (see above). It might
>look like the example I posted:
>http://www.enjoybirds.com/HowItWorks/exFFT02.jpg
>
>Now you are ready to tackle noises WITHIN the main song band. These fall=
>into two categories: those in "silences" between songs, and those within a=
>song. The first is easy, the second impossible, usually, but read on.
>6. If you want to shorten the interval of "silence" between songs as with=
>EnjoyBirds audio files -- which offends many biologists who want to
>preserve the rep-rate of the original singer -- just click and drag and
>[delete] the unwanted among-band sounds in your recording. I often do NOT=
>wish to do this, so replace these "silent" portions with Copy-Paste
>sections from the same recording, somewhere among other "silent"
>places. This is simple:
>A. mark the offending sound to find its total length (see lower right of
>screen)
>B. find a quieter part elsewhere and click and drag a same-length portion,=
>press Crtl-C to copy it.
>C. return to your offending sound, click and drag the same part of it, hit=
>Ctrl-V and the quieter part will paste-replace the offending sound. Be
>sure an listen to the whole thing several times to be sure it blends ok.
>
>7. For offending sounds AMONG your wanted sounds we could likely write
>several PhD dissertations, which would really be more useful than most
>actual ones (including mine). The key is: Structure is everything. For
>files intended only for educational species-ID purposes, with a repetitive=
>sound (like many wren calls), I have actually (horrors!#%*^&@#) copied a
>healthy part of the rep, and pasted it over the sick part - to make the
>sound come out to the proper number of reps and the proper length. But
>this is artistry not science and I am sure I will be kicked out of the AOU=
>for admitting it, and that everybody within the sound of this message will=
>. . . .never, never, never again buy my EnjoyBirds product as a
>result! The very idea! Heresy! Might as well use a Moog and be done wit=
h it!
>
>Seriously, I also use morphing filters to remove sounds that slur up or
>down, fade in and out from WITHIN songs and sounds I wanted.
>Morphing filters work exactly like the FFT filter you just built, and all=
>start with making one with the "lock to constant filter" checked.
>But if you want to remove a rooster crow, it rises then falls in
>frequency, so your curve has to follow that, or take too big a chunk out
>of the song you wanted to save. So after you nearly have it perfect as a=
>single FFT curve, and you have run it and Ctrl-Z undone it several times,=
>you unclick the dot next to "lock to constant filter" , so it reads:
>Morph. Now you have two identical filters, and you can make one higher
>pitched and one lower pitched to follow that bird (rooster)!
>
>Inexplicably, Cool Edit chooses these two filter with two boxes at the
>very top right of the window! It took months for me to discover these
>boxes, since up until now, you work from the top downward on the screen.
>"View initial filter graph" and "View final". These are two set points,
>and I discovered after much error that they only work well if the have the=
>same number of nodes in them, so the morphing process matches set points
>and can interpolate properly.
>
>It is important to understand exactly what this does: It follows the
>"Transition curve" over the course of whatever part of the sound you have=
>selected, and ranges between Initial and Final curves, depending on the
>position of the Transition Curve (TC). In the simple cas that the TC
>starts at the bottom left, and rises along a straight line to the top
>right, the program will begin with the Init. curve at the left of your
>select interval, gradually apply interpolated setting to it as it makes it=
>look more like the Final Curve, ending at the right side with the curve
>exactly like the Final one. If Final and Initial are exactly alike,
>morphing is just like a constant filter. If the initial "U"- shaped dip
>is dragged a few Hz lower in pitch, and the Final a few higher, and the TC=
>is made to begin low, rise fairly quickly, the fall beck to the bottom at=
>the end, the filter will remove the main freq. component of the rooster's=
>infamous wail. Now, all you need is to save the morph filter, e.g. as
>"rooster1" and duplicate it for the second harmonic, then the thirds, etc.
>
>Nobody said it would be easy.
>
>Although I predict that, like several of my previous posts, not a single
>person will read through all of this, let alone use any of it, I STILL
>send all my hopes for good recordings and my best regards, ;^0
>
>Marty Michener, MIST Software Assoc. Inc., P. O. Box 269, Hollis, NH 0304=
9
>
>"They that can give up essential liberty to obtain a little temporary
>safety deserve neither liberty nor safety." - Ben Franklin, 1775
>"Pues cuando ardi=F3 la p=E9rdida reverdecieron sus maizales"
>
>
>COPY: Nature Recordists Msg 376:
>
>Doug:
>
>I have DL your dove file and can tell you that I have lots of files
>that are much worse, from which I can often extract enough
>of a facsimile to produce ID teaching bird song examples.
>I had a White-cheeked Pintail from USVI, overlapping kids
>bleating for their mother's milk (uh, goats, that is), frogs in the
>same pond, and Black-necked Stilts piping to beat hell.
>
>Let me emphasize that these files are only for helping
>folks learn wild bird songs, they are not for any kind of
>scientific comparisons, and many are labeled
>"Warning, long silences have been shortened."
>(or, as: Objects in the mirror appear . . . )
>
>I have given up completely on COOLs "noise reduction"
>filters. Just when you are getting some interesting
>purification, you get all these distant bells ringing.
>And the more you listen to them, the worse of an artifact
>you decide they really are! I do it all now manually.
>Having said that, I do use many of the tricks already
>mentioned to produce a more normal-sounding final
>example. My real goal is for a learner to just say:
>"oh, that's what it sounds like." and not "What is wrong
>with that bird?"
>
>Usually, the first step is to remove clicks and crunches,
>deleting (between selected zero crossing points)
>in the time domain. Since I often walk as I record,
>foot crunches are unavoidable. I might later say
>something about how to hand hold shotguns while
>minimizing the creaks and groans of sixty-year old
>wrist joints <g>.
>
>To keep the same pacing of a longer song, I measure
>the times between each part, in milliseconds, and
>when these "silences" are plagued with loud noises
>(usually people, dogs or nearby common bird species)
>I will copy a piece of quiet ambience of exactly the same
>length, and paste-replace the noisy part. I know that there
>is a great danger in doing this that you will overwrite
>a subtle part of the bird's repertoire, so you've got to
>be on your auditory toes to do this. But this doesn't help
>when the "jaaayyyy!" overlaps with your Nightingale-thrush
>song itself!
>
>The second step is filtering, but I often use -40
>dB, which usually produces garish sounding results,
>as though coming through a culvert or from inside
>a conch shell.
>
>My favorite example was early near daybreak at
>the Cockscomb Jaguar Sanctuary in Belize when
>I had three species singing at once, all new to my library,
>and they were mutually completely separable in their
>frequency spectral bands. So, I finished with three
>20 second digital files from the same 20 seconds of
>DAT tape! That was less than 24 hours before the
>DAT became useless, ostensibly from humidity.
>
>I also make very specific (morphing) filters for
>many of the common species of birds, esp.
>the corvids, where I go through a recording and select
>specific non-target sounds and morph filter them
>into annihilation, like a frequency domain surgeon.
>Watching in the spectral mode, the file will grow to
>have black slices out of it where the jay or crow
>previously had made the file useless for teaching.
>I have literally hundreds of filters saved, named
>for each species they exclude, e.g. de-LEPVER
>for one that removes Leptotilla verreauxi. As we
>all know, human voices are the toughest, since
>our ears are exquisitely sensitive to murmurs of
>other humans.
>
>I then frequently use a file from which recognizable
>specific sounds have been removed, as a source
>of ambient hiss or whatever you wish to call it, and
>perform a complimentary filtering on it, so it provides
>the noise frequencies obviously missing from my brutally
>freq-filtered original. Then I use a mix paste, as has
>already been mentioned, to produce a more normal
>sounding result. I will frequently use COOL
>Ctrl-Z to undo, then F2 to re-try a filter or mix-paste,
>trying different levels until it sounds best.
>
>BTW I use a Bose Acoustimass system on my
>computer, rather than headphones, which tend to rot
>my ears in hot weather.
>
>As we all know, the expensive part is the time spent in
>Jamaica, Panama or Costa Rica, not that at the computer.
>
>I am not at all proud to perform this analog of cosmetic
>surgery, any more than a liposuction patient posts his operation
>on his web site. But if it helps me or others learn the songs
>better - it seems worth it.
>
>my very best regards,
>
>Marty Michener
>MIST Software Associates, Inc.
>75 Hannah Drive
>Hollis, NH
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