Hi David,
Microphone self noise will certainly be a more important factor than polar plot
as I think a cardiod with 5dB (or two of them even better)could record a more
distant subject more clearly than a long gun with 10db. A highly directional
mic may isolate a specific subject better in certain circumstances, but I do
not see how that effects comparable perceived distances.
John Hartog
rockscallop.org
--- In "Avocet" <> wrote:
>
> > I just wondered if members would be willing to share more info on
> > their microphones commonly used in the field.
>
> With trainees, I used the idea of "fetch" - similar to "reach" but
> more definable. It is basically the image distance judged by your ears
> alone, compared to a single cardioid.
>
> ("Reach" is a different concept more related to the maximum useable
> distance.)
>
> Imagine a bird singing in a tree in the garden or on the roof. With a
> quiet background, a single cardioid will get you a good recording at
> 10 yards (metres for those in the 21st century) if the bird doesn't
> fly away. An omni would need to be about 5 yards for a comparable
> recording, so has a fetch of 1/2, but the bird has gone by now.
>
> Short gunmics are the workhorse of most outdoor recording and score a
> fetch of about 3, so the bird on the roof would still sound good at 30
> yards.
>
> Long gunmics have a fetch of at least 5 and will bring in stuff you
> couldn't get otherwise, like shy wildlife. They need to be aimed
> accurately and are expensive, and heavy when mounted in a good blimp.
> These mics are much less directional at low frequencies so a gentle
> bass roll-off is often needed.
>
> Parabolas are very different. They have a fetch of more than 5 at bird
> frequencies but are even more frequency dependant than long gunmics.
> They have to be accurately aimed at a source for best results. They do
> have a very useful advantage as they focus the sound, producing an
> acoustic gain which often swamps any mic noise.
>
> (Plug for the Brinibox rig which has a gain of about 12dB and can use
> crap mics.)
> http://www.stowford.org/sounds/brinibox.htm
>
> Cost is important of course, but what you really pay for between
> affordable and pro mics is a low noise level. Frequency response is
> good in most mics nowadays on-axis, but off-axis even the most
> expensive gunmics are all over the place.
>
> Stereo is a whole new ball game and adding a second mic will reduce
> the fetch by about half. In real life background noise is less
> apparent to the ears as our brains can select what to listen for, and
> this is also true to some extent with a stereo recording.
>
> Almost all stereo rigs are equivalent to a pair of cardioids with a
> low fetch, but often with a good stereo image. Nice sound but you have
> to get closer. I use crossed gunmics which is a clumsy rig but it
> retains a good fetch. Here's a woodpecker at 60 metres:
> http://www.stowford.org/recordings.htm#woodpeckerbeech
>
> A problem arises when adding a sideways fig-8 to a gunmic to make an
> M-S pair. When this is decoded to L-R stereo, the pickup is near omni,
> almost back to a fetch of 1/2. The good news is that the gunnmic fetch
> of 3, say, is still available in mono. These "zoom" mics are often
> used on video cameras, but the S signal is picking up very little that
> is in the picture.
>
> David
>
> David Brinicombe
> North Devon, UK
> Cogito cogito ergo cogito sum - Ambrose Bierce
>
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