reply to post by rickyrrr
Yet again obfuscation and not a single relevant point to add to the conversation all based on casting aspertions about my knowledge. Let me get this
right. You,. who have zero knowledge about recording and acoustics are challenging my level knowledge and trying to quantify it against someone
else's knowledge. That is brilliant. So someone who knows nothing, is now sitting in judgement of my experience. You made an outright accusation that
i didn't know what i was talking about and had just copied stuff from Wiki and expect to be treated with any respect. That is some breath taking
arrogance from you and typical of some of the almost troll like skeptics on this board. Oh you can s dish it out,but can't take it yourself can
i happen to think it has been faked . However, the reasons, so far, given for the audio track being fake, have very little basis in any understanding
of real world technology and how it works.
Just for you i shall repeat what i posted, as you obviously have a slight cognitive problem. Most cam corders have a built in stereo microphone. That
microphone is often situated. flat mounted, under the lens or just to one side. These mics are usually a very cheap affair that means they are, to all
intents and purposes, unidirectional in their nature. That is, they pick up over a relatively shallow field and off axis sounds are not picked up with
anything like the accuracy of a typical studio condenser/ribbon mic.
The net effect of that is that the perceived stereo image, on playback is a very narrow one and at times can appear to be, what is known as dual mono.
However, with something as extreme in level as low flying jet engine there would be enough level to give more obvious stereo effect. Part of the
reason for this is explained by the what is known as *psycho acoustics*, that is the way the human ear perceives sound in relation to its frequency.
In short, and for those who aren't au fait with the subject. Low bass is perceived by humans as omni directional. That means, low frequency noise
seems to emanate from everywhere and are hard to pinpoint their exact source. Higher frequencies, the human can, pinpoint their exact position in a
sound filed. With a jet engine, you have a pretty broad spectrum of sound from very low bass or huge amounts of air being sucked through them and
pushed out, to the high pitched whine of the turbine blades rotating.
it is possible, although in my opinion unlikely that, the audio track could be genuine for the following reasons.
The inbuilt mics on camcorders do not have a big enough diaphragm to allow them to record anything much lower than 150hz, with any sort of accuracy.
In effect, the inbuilt mics act as their own high pass equalisation filter. Combined with many of these mics have a built in limiter, that is, when
the signal recorded reaches a certain level, 0db, it automatically reduces the level of any incoming signal that is louder than that.
I would hazard a guess that those jets as the passed would be producing a level of signal somewhere in the 120 decibel and quite possibly more. That
means they would automatically trip the mics inbuilt limiters and you'd expect to hear something that sounds far more ragged and distorted than that
you hear on this soundtrack.
However, as there are two jets there a possible get out clause. it is feasibly possible that, the presence of two jets with the same engines
travelling at roughly the same speed in close proximity could produce some phase cancellation. The net effect of this would be to lower the perceived
level one hears, or a microphone picks up from the two planes and affect how the human ear perceives the stereo sound field. phase cancellation was
and is used, at times, for the generation of those *freaky* stereo sound effects on some albums.
Now back to the Doppler effect...
The mics built into most camcorders, because they have such a limited field or sound perseption cannot produce an exaggerated Doppler effect. If you
want o understand what i am talking about simply do the following. Listen to some music sitting between two speakers. The cup your ears and push them
forwards to narrow the range your ears can pick sounds up from and listen to the same music. That is way more like what your typical camcorder mic
hears and records.
However, because of the nature of the loudness of jet engines and that they cover frequencies which are, in music terminology, very directional, I can
see a scenario where, the inherent weaknesses of cam corder mics, could actually produce just the right effect. Plus, given there are two jets and
there could be some phase cancellation helping this out, it is possible that the soundtrack is genuine. Personally, i don't think so, but unlike the
vast majority of people on this forum, i do have some understanding of the science of why it might be genuine.
To summarise, under normal circumstances the mics on your typical cam corder cannot, by their very nature and positioning produced a pronounced
Doppler effect. However, because of the very nature of jet engines and how loud they are, plus, there are two jets in tandem, thus with the
possibility of phase cancellation affects,, there is a probability, greater than zero, that the soundtrack is genuine.
I reiterate the point that. People who bandy terms around like*Doppler effect* without any real understanding of its nature under vastly different
systems and circumstances, are indulging in the same pseudo science many of the loony believers are accused of.
The waters are further muddied by the fact that. One has to assume, if this footage has been uploaded from a news channel that it has been not
visually edited, but the audio track has been edited as well. it could well be that.The soundtrack with the jets was so badly distorted that it was
deemed not of broadcast standard. That being so, the editing crew were told to overdub the commensurate jet engine noise after. This * Foley* work is
not unusual, even in news footage, where the raw tape was obtained under extreme circumstances. in this situation the problem is that, by doing such
work it lays the footage open to accusations of it being fake.
[edit on 30-9-2009 by FireMoon]