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Re: Responses to ambient sound recording

Subject: Re: Responses to ambient sound recording
From: "Avocet" madl74
Date: Tue Nov 30, 2010 4:40 am ((PST))
> Is there an opinion about whether the
> speaker should be set-up at 1 meter?


The mic to speaker placing could be critical. At 1 metre you would
still have phase relationships with different parts of the speaker
cone, box resonances, and reflex ports if any, but ground reflections
would be minimised.

As an overall check on resonances and reflections try recording a slow
sweep tone across the whole range. My guess is that this will be very

The mics will also be picking up a ground reflection of the speaker
depending on the ground surface. It may well be useful to baffle off
the direct sound, reflecting it into the air, to see what sort of
reflections they are picking up. Soft grass is a good absorptive
surface for most frequencies.

To minimise standing wave patterns mic testing is usually done with
warble tones which is why frequency response curves are usually
smoothed out. I've got a combination bandwidth limited 800Hz to 1200
Hx white noise and warble at:
I made this with Audacity 1.3 which has an easy Equalization function.
This will copy exactly end to end or you can use loop play. You can
also shift the frequency t    o save recreating bandwidtht limited 
noise and/or warble tones each time.

> I guess we'll see if the 1000 Hz tone produce a different RMS A
> measurement and explore the significances.   Rob D.

I've also got a test tone which I originally devised for adjusting
tape azimuth in the field, avoiding false peaks as you get with pure
tone. It is very phase sensitive and is based on 440HZ (musical chord
A major) with subharmonics and harmonics from 44Hz to LPF rolloff.
This will also copy end to end or loop play.

BTW if you want to see mp3 artifacts try compreessing brinitone.


David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce

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