Normalize first or filter first

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Normalize first or filter first

Postby citguy » Thu Feb 03, 2005 7:06 pm

The recent discussions on normalizing have got me rethinking my logic on whether to nomalize then apply filters or filter then normalize. Logic would suggest that normalizing after filtering would bring background noise back up with the content, but logic does not always reach the correct conclusion. I just did a 40 year old reel to reel tape and did the procedure BOTH ways. I was hard pressed to tell much difference but thought I might have heard more inter-channel crosstalk when I normalized first. I concluded that to filter then normalize and then filter one additional time is not good.
Stan
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Re: Normalize first or filter first

Postby adaywayne » Thu Feb 03, 2005 8:07 pm

citguy wrote:The recent discussions on normalizing have got me rethinking my logic on whether to nomalize then apply filters or filter then normalize. Logic would suggest that normalizing after filtering would bring background noise back up with the content, but logic does not always reach the correct conclusion. I just did a 40 year old reel to reel tape and did the procedure BOTH ways. I was hard pressed to tell much difference but thought I might have heard more inter-channel crosstalk when I normalized first. I concluded that to filter then normalize and then filter one additional time is not good.
Stan


Normalise after declicking and applying any filters, I say. This way (1) loud clicks are not used as the peak. (2) Applying filters can change the overall volume as well as the detected peak so it ,=]makes sense to filter first.
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Postby Derek » Sat Feb 05, 2005 3:15 pm

Yes, the best approach is to normalise after you have finished other processing.

It is true as the original poster said, that normalising will increase the noise along with the signal. However the net effect on signal to noise ratio (the important parameter) is exactly the same. To take an example, say you have a file where the signal peak is -7dB and the noise floor is -50dB. The signal to noise ratio is therefore, 50 - 7 = 43dB.

Signal = -7dB
Noise = -50dB

1. Apply hiss filter (at 14dB setting) and then normalise (to -1dB):
1a. Hiss filter:
Signal = -7dB (no change)
Noise = (-50 -14) = -64dB
1b. Normalise
Signal = (-7 + 6) = -1dB
Noise = (-64 + 6) = -58dB


2. Normalise ( to -1dB) and then apply the hiss filter (at 14db setting)
2a. Normalise
Signal = (-7 + 6) = -1dB
Noise = (-50 + 6) = -44dB

2b. Hiss filter:
Signal = -1dB (no change)
Noise = (-44 -14) = -58dB


So you see that in both cases you end up with the same result.
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Postby adaywayne » Sun Feb 06, 2005 4:58 pm

Derek wrote:Yes, the best approach is to normalise after you have finished other processing.


2b. Hiss filter:
Signal = -1dB (no change)
Noise = (-44 -14) = -58dB[/color]

So you see that in both cases you end up with the same result.


I was thinking more about applying equalisation. If one normalises first and then applies a bass or treble cut, it is possible, is it not, to end up with a "signal" peak at lower then -1dB?
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Postby Derek » Sun Feb 06, 2005 5:16 pm

adaywayne wrote:
Derek wrote:Yes, the best approach is to normalise after you have finished other processing.


2b. Hiss filter:
Signal = -1dB (no change)
Noise = (-44 -14) = -58dB[/color]

So you see that in both cases you end up with the same result.


I was thinking more about applying equalisation. If one normalises first and then applies a bass or treble cut, it is possible, is it not, to end up with a "signal" peak at lower then -1dB?


Yes, that's true. I was just illustrating that there is no advantage to normalising before filtering. I agree it can be a disadvantage as in the case you cite.
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