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Re: noise cancelling

Subject: Re: noise cancelling
From: Klas Strandberg <>
Date: Tue, 12 Feb 2002 03:34:50 +0100
Yes, it makes sense.

Klas

At 12:57 2002-02-11 -0500, you wrote:
>Klas:
>
>I use a monaural Telinga with an MKH 20 mike. So all I'm doing is using a
>Y-connector to add an additional mike (in this case another MKH 20 omni) t=
o
>the input of the tape recorder. I'm also re-wiring the XLR cable to this
>omni in order to reverse the phase. I can then move the second omni around=
,
>placing it within the reflector, along it's edge, or wherever to get the
>optimal noise reduction.
>
>Lang
>
>> I'm sorry, but I can't figure out what you are doing.
>>
>> 1/ You can use a parabol with a OMNI mic connected to one stereo channel=
.
>> 2/ you can have the SAME type of omni connected to the other stereo chan=
nel.
>> 3/ you can connect the headphone output, so that one of the channels is
>> inverted, and the    two channels into mono. (you will need 2 transforme=
rs
>> to do this, or electronics doing    it)
>> 4/ Now you can have the parabola on a tripod, and by random, move the ou=
ter
>> mic around       until you get "best" noise reduction. This process cann=
ot
>> be predicted or calculated,     as you have no facts to base your predic=
tion
>> on.
>> 5/ The frequency you will filter out, will be dependant on the wave leng=
th
>> vs. the    distance between the mics. If the noise is broadband, you wil=
l
>> filter only a part of
>> it.
>>
>> I don't know what happens if you try to do this with directional
>> microphones. It feels like you are going into a total chaos of parameter=
s
>> which you can never get control over.
>>
>> Using an outer mic for noise cancelling, is VERY experimental, only.
>>
>> Klas.
>>
>>
>>
>> At 00:50 2002-02-11 -0000, you 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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>>>>
>>>> Telinga Microphones, Botarbo,
>>>> S-748 96 Tobo, Sweden.
>>>> Phone & fax int + 295 310 01
>>>> email: 
>>>> 
>>>
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>> Telinga Microphones, Botarbo,
>> S-748 96 Tobo, Sweden.
>> Phone & fax int + 295 310 01
>> email: 
>> 
>>
>>
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>
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Phone & fax int + 295 310 01
email: 
       



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