I am Back from recording winter finches.
Will try and respond to a few different messages in one.
Rob wrote:
>It seems like part 3 shows
>something like a -6dB roll-off starting at about 700hz. The distant
>machine is centered around 240 hz. Do you think pt 3 is effectively
>cancelling more in this Hz area?
I think that the most cancelled noise is not frequency dependent but
is the sounds that are diffuse and in front of the dish so that each
element captures a similar image. Sounds that are a full 90 degrees
to the side I am having trouble cancelling because of volume
differences. I believe if I would spin the capsules to be
perpendicular to the noise that needs to be cancelled I would get a
better result.
John wrote:
>Thanks Rich, for your picture of your mic configuration and
>the audio clip. I find your method of noise reduction
>interesting.
>Here's a picture of how my Shure WL183s are currently
>mounted:
>http://www.hevanet.com/rockscallop/183sInDish.jpg
Similar indeed. We both need to work on getting the capsules to see
more of the dish.
Umashankar wrote:
>have you tried mounting the capsules in axis, one mic
>slightly behind the other. that way, if one mic is in
>focus and the other is not, phase cancellation should
>leave behind only the sound focussed on by the dish.
Yes, I have tried both in line as well as putting the second capsule
on the rim of the dish. Before that I tried a separate shotgun mic on
the rim pointed at the noise to be cancelled. I reported on the rim
technique about a year ago and did I see a TV network using this
technique at NFL football games this season? Someone is always paying
attention. I prefer the side to side technique I currently use
because the majority of time I am not going to use the second channel
for noise cancellation but rather for a stereo recording. I suppose
one could use four capsules and get both stereo and noise cancellation.
Walt wrote:
>In both Rich's and this example there is a barrier between the mics (the
>support tube) such that the mic's may not "see" the whole dish. Since
>the tubes are large relative to mic size I'd assume they have some
>effect. Has this effect been calculated or measured?
Yes I need to cut up or replace the support tube so that more of the
dish is seen by each capsule. I still want the barrier effect in
front of the capsules for the sounds way off axis but that support
tube is a current problem. I have tested the effect of a full barrier
on the image and will simply say I personally did not like what I saw
and heard. But since you already own the comparitive mics anyway,
take a look at one channel output from your telinga stereo mic
compared to the output from the telinga mono mic when they are pointed
at distant pink noise. There are plenty of people that find the
results of the stereo telinga ok. I just feel it can be improved upon
with trade offs.
Rich
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