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Re: Software for frequency measurments

Subject: Re: Software for frequency measurments
From: Klas Strandberg <>
Date: Thu, 03 Jul 2003 13:25:24 +0200
It doesn't matter if my "leveler" don't work perfectly. Please note that I
don't measure true frequency curves, as in a laboratory, but rather curves
only to describe a change from one set up to another. Example: What happens
if I put an omni facing forward, compared to if I put it facing inwards the
dish?

It is one thing to hear such a difference between two set-up,s but it gives
further information when you can also see it at a diagram.

Besides, when doing these measurment with a parabol, at 30 meters distance,
I only measure frequencies over 300 Hz.

Using a loudspeaker only, at that distance, - without the leveler - will
give figures full of peaks and gaps. Such measuments are difficult to
compare. You don't see "the average". My leveler flattens out such peaks an=
d
gaps to some +/- 3 db, which is good enough to see "patterns" with two
measurments.

Besides blowing the HF speakers, there is no problem measuring analog. Thre=
e
or four measurments in a row will tell if there are unwanted bias with the
measurment. If they look the same, all is well.

If it is really quiet outside so that I can run the speaker at a low volume=
,
I can also check the 30 sec sweep with a long sweep, say 5 minutes, and
compare.

But I want to go digital now, mostly because I want to simplify. It seems a=
s
if the FFT meter can do the job if I can only learn how to handle it right.=


Klas.




At 17:32 2003-07-02 -0700, you wrote:
>>As it is right now I use a 30 sec sweep. But If I record on tape and can
>>analyze the recording with a software, why should 1 sec be too short?
>
>Accuracy at low frequencies takes time. I think averaging many
>repetitions of the fast sweep can have the same effect.
>
>>Dan, anybody - what is a FFT-meter? It's with my editing program also wit=
h
>>Cool Edit, I think. It looks like a frequency curve and it seems to work =
as
>>a such. If I record a logarithmic sweep 20-20.000  Hz in one second, then
>>make a .wav file of it and ask the FFT analyzer display it - will it show=
 a
>>common frequency curve, as we know them from before computers?
>
>No, it's a real-time analyzer, more useful for looking at pink noise.
>But with pink noise you can't do the level correction that you do
>with your sweep source.
>
>BTW, I can't imagine your level-correction loop can work that fast either.=
..
>
>-Dan
>
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Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email: 
       



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