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Null tests
Old 22nd September 2010
  #1
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thesteve's Avatar
Null tests

I've been doing some reading regarding how to interpret the results of a null test where the two pieces of audio do not completely cancel when the are flipped out of phase. This has come up because I recently tracked a vocal split through a radial mic splitter into an ssl VHD and a great river me2nv. The "vhd" knob was set very high, so there was significant distortion on one channel. The G.R. was pretty clean.
The tracks null to about -54 (using waves Paz meter for measurement).
I had read somewhere that a result of nulling to -60 would be an eqivelant of having two pieces of audio that are indescernable to the average ear.
So, the issue here is, of course, that the two tracks sound very different but null down close to what is considdered inperceivable.
I have no conclusions, and I am also a "mix with your ears" kinda guy so in a way I don't care. I have just been seeing so many references to null tests and the like that I thought I would check this out.
Old 22nd September 2010
  #2
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JoaT's Avatar
"null down close to what is considered inperceivable"

You answered your question right there.

Close, but not quite inperceivable. And Close to what is considered. If something is considered there's always people who will claim it is insufficient.

My 2 cents.
Old 23rd September 2010
  #3
Gear Guru
 
Ethan Winer's Avatar
 

Quote:
Originally Posted by thesteve View Post
I had read somewhere that a result of nulling to -60 would be an eqivelant of having two pieces of audio that are indescernable to the average ear.
That's probably true. If the difference is 60 dB down it's unlikely you'd hear it due to masking. It's also possible to have two sources that don't null very well but still sound the same. For example, a microphone recorded through two different sound cards might drift slightly over time. So you'll get a good cancellation, but after 1/4 second the null goes away. Phase shift is another reason that two sources may not null, even if the sources sound the same. Phase shift is not usually audible, but it can prevent nulling.

One good way to compare similar sources is with an FFT analyzer. Many audio editor programs have this feature, and it can show the spectral content to very low levels at high resolution.

--Ethan
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