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Hi-Pass Filterin'

 
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D Voice
Been Here Awhile


Joined: 26 Jun 2010
Posts: 232

PostPosted: Wed Aug 17, 2011 8:41 pm    Post subject: Hi-Pass Filterin' Reply with quote

Specifically, I was doing a non-critical recording with a SP C-1 into a PreSonus TubePre (with the -pad on) into a USB mixer.
All 3 have items in the chain have High Pass roll-off switches

But it brings up a generic question:
Where to do the high-pass filtering? And is this a hard-and-fast rule, or does it depend on the equipment.?

For one reason or another, I have been led to believe that:
a) you don't want to do the filtering on more than 1 outboard device
b) you want to do the filtering at first item in the chain (the mic if it has one; otherwise the pre-amp).

If so, why?

Are these both ALWAYS true, and if not, when/why not?


I guess in normal conditions, it is rumble and vibrations that is best to filter out those.
But do the (tube-ish) mic pre's possibly create some noise at the low end that should be attenuated at the pre or at the mixer?

TIA
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Mike Sommer
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Joined: 05 May 2008
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Location: Boss Angeles

PostPosted: Wed Aug 17, 2011 10:03 pm    Post subject: Re: Hi-Pass Filterin' Reply with quote

Quote:
Where to do the high-pass filtering?

Generally Mic Rolloff Switches were once intended to be used when mics are used out doors, particularly on windy days, or if you are in a very boomy room or there are any low frequency noise in the background, the rolloff can cut most of that out.

Personally I've never used a mic's rolloff switch, I will use the rolloff on a mixer before I use a mic's. Why? That's just me, and I know the frequency rolloff of the mixer better then I do all the mics.

Let's understand, there is noting useful in the human voice below 80Hz, if you hear a difference in your vocals when you use an 80 or 75Hz highpass or rolloff, more than likely it is room resonance and bass build up, and your room needs treatment.


If we use compression on vocals, we want to use a Highpass or rolloff before the audio goes into the compressor, so the compressor does not "Pump" or compress to the powerful bass frequencies.

Quote:
And is this a hard-and-fast rule, or does it depend on the equipment.?
No, just do what sounds good: Record, Listen, and Compare your audio files. Learn what sounds good and what does not. If you need help, run it by us.

Quote:
a) you don't want to do the filtering on more than 1 outboard device
If you can do that, and have the proper gear and it sounds good - do it out board first. I've always said, develop your sound outside the computer first. One you're all dialed in, all you need to do is simply record, do a few edits and go.

Quote:
b) you want to do the filtering at first item in the chain (the mic if it has one; otherwise the pre-amp).
Sometimes yes and sometimes no. Just do what sound the best. I generally roll off after the preamp, before it goes into an outboard compressor. If you are going directly into the DAW you can rolloff before it goes in. Or you can do it in the DAW.

General rule of thumb:
Anytime you want to take away something do it before the compressor If you want to add something (EQ boost echo etc..) do it after the compressor.


Quote:
Are these both ALWAYS true, and if not, when/why not?

Nothing is right or wrong- there may be a better way of doing something but there is never a Best Way. Do what sounds good to you.


Quote:
I guess in normal conditions, it is rumble and vibrations that is best to filter out those.
Of course!! that goes without saying.


Quote:
do the (tube-ish) mic pre's possibly create some noise at the low end that should be attenuated at the pre or at the mixer?

Depends. Sometimes they can add roundness and fullness, they can be tubby, sometimes they can sound thin. BUT they only work with the frequencies that are given to them. If pushed tubes can even create there own compression, which gives the illusion of more bass, but it's only the compression increasing the quieter parts. That's what compression does.
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georgethetech
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Joined: 18 Mar 2007
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PostPosted: Wed Aug 17, 2011 11:25 pm    Post subject: Reply with quote

In other words, what Mike's sayin' is "if it sounds good, it IS good".
There are no hardset rules when it comes to this stuff. Record versions with of the different HFP's engaged and listen... Don't trust your ears? Post 'em here.
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D Voice
Been Here Awhile


Joined: 26 Jun 2010
Posts: 232

PostPosted: Thu Aug 18, 2011 12:00 am    Post subject: Reply with quote

Thank you, gentleman.

So I am trying to get my head around this.
Where in the circuitry does the high-pass filter affect the signal? Before it is amplified, or after?

I guess an example would be, a pre-amp:
if the preamp were adding adding any low end noise, would the hi-pass filter reduce that, or only noise that comes down the line from the mic?
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