on 13/2/02 5:44 AM, richpeet at wrote:
> Well last time I made a suggestion I ran you down a dead end.
> But you may enjoy trying your pair of me-64's using one on subject
> and one off. Then try inverting one channel and converting to mono
> and see if you get a reduction in background noise.
Rich and All,
I tried this but with ME67 plus ME64. There were cicadas and a small plane
as "unwanted", and a Grey Shrike-thrush song as "wanted". The experiment,
brief as it was, showed some lessening of noise level when the noisy channel
was later inverted in Peak and mixed with the wanted sound. But there was
also slightly more hiss, and a slight diminution of the bird's song. I'll
try it sometime with two ME 64s, just to be sure I haven't imagined the
effect. (Your JPEG looked very convincing!)
Meanwhile I am mounting the two ME 64s in the ORTF combination that Lang
suggested, and have now made a shock mount with rubber bands and coat-hanger
wire, I'm about to cover that with "bear fur".
Vicki Powys
Australia
>
> I don't know how the filtering works from a programming viewpoint to
> understand why it defeated your purpose on the test you tried.
>
> I am still trying to understand the cancelling effect I was able to
> achieve and doubt if I will. I will try some more simple and
> controlled tests. But it does look very worthwhile so far.
>
>
> good luck
>
> --- In Vicki Powys <> wrote:
>> on 11/2/02 11:50 AM, richpeet at wrote:
>>
>>> Ok I tried this in cool edit. I took a Mono track, converted it to
>>> Stereo, inverted one track, and reconverted it to mono. Sure
> enough
>>> there was no signal left.
>>
>> Rich and All,
>>
>> I've just tried inverting a sound track in Peak, then mixing it
> with the
>> original. Same result as Rich - complete cancellation of the
> signal, very
>> dramatic! So I thought to make use of this effect by selecting
> just the low
>> noise out of a recording (using Q10), then inverting that noise,
> then mixing
>> it back with the original. It has no effect at all. The fact that
> I had
>> passed the signal through the filter seemed to upset the process
> somehow.
>> If you wanted to use phase cancellation as a noise reduction method
> from the
>> files in the computer, how would you do this? I guess it is easier
> to use
>> band pass filtering, but I'd still like to know how to use phase
>> cancellation for noise reduction on processed sounds. Anyone know?
>>
>> Vicki Powys
>> Australia
>>
Rich wrote:
>>> I tried the hardest test I could come up with.
>>> Here is sparrows recorded at ~150 feet with a highway directly in
>>> back of the sparrows, an interstate 1/2 mile behind, in a 10 mph wind.
>>> two identical mics, me 62. one in a 32" parabolic, one directly over
>>> the first by 24" outside the parabolic. The channel outside the
>>> parabolic was amplified 50%, inverted, and combined to mono. First
>>> half of the recording is the parabolic only second is the combined
>>> result of the two channels. What you can not see is which birds were
>>> directly in the parabolic path and which were not.
>>>
>>> a large 1.5 meg for the wave file
>>> a small 39K spectragraph for the jpg file
>>>
>>> see
>>> http://people.mn.mediaone.net/richpeet/nc.wav
>>> and
>>> http://people.mn.mediaone.net/richpeet/nc.jpg
>>>
>>> files will disappear by the end of the month when the isp goes down.
>>> they are then avail upon request once i change my e-mail
>>>
>>> What ya think?
>>>
>>>
>
>>
>>
>> on 11/2/02 11:50 AM, richpeet at wrote:
>>
>>> Ok I tried this in cool edit. I took a Mono track, converted it to
>>> Stereo, inverted one track, and reconverted it to mono. Sure
> enough
>>> there was no signal left.
>>>
>>> Now I run a ME 67 long shotgun over my 32" dish. My original
> thought
>>> was to be able to aim my narrow 32" dish and cya when I overrun
> the
>>> preamp on a loud recording received by the dish. But I also see
> that
>>> I can pivot my shotgun because of the way I mounted it and will be
>>> able to point it at single source noise problems, invert and
> cancel.
>>>
>>> How far away can I have the diaphrams of the two mics before I
> can no
>>> longer use this technique? Is 24" to far?
>>>
>>> --- In Klas Strandberg <>
> wrote:
>>>> Using a mono parabol, you can have an extra omni outside of it
> and
>>> connect
>>>> it antiphase. By moving it, you can "tune" your filtering to the
>>> noise which
>>>> is present. The remaining noise is the noise which is reflected
> by
>>> the
>>>> parabol "only".
>>>>
>>>> Klas.
>>>>
>>>>
>>>>
>>>> At 14:21 2002-02-10 +0100, you wrote:
>>>>>> Date: Fri, 1 Feb 2002 09:39:46 EST
>>>>>> From:
>>>>>> Subject: Re: noise filtering 101
>>>>>>
>>>>>> Jeff,
>>>>>>
>>>>>> You audio sounds pretty good after being filtered. Here is a
> few
>>> things I do.
>>>>>> When I have recordings with car noise, I first use the FFT
>>> filter to do a
>>>>>> 85dB rumble cut for anything below 120Hz. That gets rid of wind
>>> noise too.
>>>>>> When I use noise reduction, I get the profile from the sample,
>>> manually
>>>>>> select a line just over the green noise signal, and reduce
> noise
>>> by 80dB. I
>>>>>> noticed your settings are at 40dB. I usually keep the noise
>>> reduction level
>>>>>> slider on the low side. Overdoing noise reduction ruins the
>>> quality of the
>>>>>> audio, so you might have to play around a little. Cool Edit Pro
>>> has a hiss
>>>>>> reduction plug-in that seems to work better than noise
>>> reduction. There are
>>>>>> other noise reduction programs available, such as Algorithmix
>>>>>> (http://www.algorithmix.com), that may work better than Cool
>>> Edit. I gave up
>>>>>> trying to get quality audio anywhere near highways, railroads,
>>> and airports,
>>>>>> but sometimes that is a luxury that can't be often found.
>>>>>>
>>>>>> The only thing you can do about faint recording is to either
> get
>>> closer to
>>>>>> your subject or get a preamp for your mic. For noisy
>>> environments, getting
>>>>>> close to your subject is critical for quality recordings. Did
>>> anyone ever
>>>>>> think of putting a mic with a long cable on a remote
> controlled,
>>> camouflaged
>>>>>> model boat? Sounds like it could work.
>>>>>>
>>>>>> Bruce
>>>>>>
>>>>>
>>>>> I experience a continuing growing problem with noise.
>>>>> Because of growing population there is always some kind of
>>>>> unwanted noise somewhere. You can name them all, plains,
>>>>> trains, highways, farmers with machines or a loud radio on
>>>>> some populair station. Is it the right way in using all
>>>>> kinds of systems afterwards? I experience the same problems
>>>>> with overdone or degrading the wanted sound too much by
>>>>> cutting too much. With computers today all kinds of
>>>>> unbelievable filters can be used. But with severe cutting
>>>>> you degrade the wanted sound often too much. I'm wondering
>>>>> if it might work when you use a hightech filter between the
>>>>> mic and the recorder or by using a shotgun with an out of
>>>>> phase random mic for noise canceling. I suppose its not an
>>>>> easy task because you have too set the equipment to a
>>>>> certain level so your ready for recording instantly. Whats
>>>>> your opinion about this?
>>>>>
>>>>> Joop Nijenhuis
>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
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>>>>
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