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Topic: spectrum analyzers: weighting

Kelsey Black
Film Handler

Posts: 58
From: Pima, Arizona, USA
Registered: Aug 1999

posted 02-16-2002 01:11 AM

I am using a software-based spectrum analyzer to do b-chains in my theater. The software has different scaling modes, flat, a-weighted, b-weighted, and c-weighted. I have had the best results with a-weighted, however the dialogue just blends in with everything else...
I am trying to set the curve to academy, flat to 2k and -3db per octave.
Am I missing something here? (besides a R-2, of course)

Kelsey Black

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Ray Derrick
Master Film Handler

Posts: 310
From: Sydney, Australia
Registered: Sep 2001

posted 02-16-2002 03:54 AM

Set the analyser to flat or c-weighted when doing equalisation and to C-weighted when setting the SPL level. Do not use A-weighting at all. If you use A-weighting you will end up with way too much top and bottom end when you equalise and your SPL setting will be far too high.

The problem with using PC software based analysers is that usually you are restricted to one mic (very bad) and the level calibration could be anywhere (even worse) unless you have the means to set it correctly. My advice is don't use a Radio Shack (Tandy) SPL meter as a reference for this, they are too inaccurate.

------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

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Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 02-16-2002 08:08 AM

Randy and others,

A question, perhaps a bit OT: I would like to have a RTA for my Home Theater room. If I have the software and the PC, how much money can I pay a good microphone? What kind of microphone should I buy?
Will the result be at least "good"?

Thanks
Antonio

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Kelsey Black
Film Handler

Posts: 58
From: Pima, Arizona, USA
Registered: Aug 1999

posted 02-16-2002 08:32 AM

Thanks Ray for the quick reply. I imagine this might belong in a different topic, but it fits in with the same subject...

In lieu of a real multiplexer, could I use a 4-channel mic mixer and 4-identical mics?

Kelsey

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Kelsey Black
Film Handler

Posts: 58
From: Pima, Arizona, USA
Registered: Aug 1999

posted 02-16-2002 08:46 AM

It looks like I have just found the answer to my own (second) question at this forum

of course, comments are welcome...

... at least I increased my posting count, something I don't do near as often as I should.

Kelsey

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 02-16-2002 09:55 AM

Talk about weighting....just take a look at my profile on the left!
Mark @ GTS

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Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001

posted 02-16-2002 10:14 AM

Antonio:
You don't need an expensive microphone to get reasonable results. You should use a small omnidirectional electret condenser midrophone - NOT a dynamic type designed for live music use. Any "vocal" mic will have poor directional and frequency response for this use.
These tiny microphones are inherently pretty good - actually quite difficult to make so that the response is not flat.You can get them at any electronics store, they are used in almost every device that has a built-in microphone like telephone answering machines, cassette recorders, etc etc etc. They are usually a tiny metal can with a wire attached at one end and a hole or bit of screen at the other.
The ones used in professional multiplexers are carefully nade, and matched for rosponse and output level - but are essentially the same.
You won't have any calibration for SPL but the actual spectrum response you see should be reasonably accurate.
There are "self pwered" versions and ones that need external DC power - the latter are generally better and the circuit to power them from a 9V battery is simple, just use a good quality blocking capacitor.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 02-16-2002 10:18 AM

Most of the PC analyzers allow for a offset correction curve so take a drive out into the country and put the mic on a stand in a farmers field (on a calm day) and that should be a flat reading and generate an offset from there

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Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 02-16-2002 02:09 PM

Great!!

Thanks for the info!

Gordon,

I didn't know that in a farmers field you can have a flat response...

Bye
Antonio

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 02-16-2002 02:22 PM

Depends on the farmers daughter

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