High Pass Filters

[markjazzbassist]

I've been reading a lot about using High Pass filters in the mix/tracking stage to help there be separation between the keys/guitar and bass/kick.

How many people are high passing stuff and what are you using and how are you using it?

Is this a more modern technique or have engineers always been high passing sources?

Do you find you EQ less if you HP, or do you just EQ an not HP?


Sorry for all the questions, i'm just very curious about this technique.

[groover]

First of all high pass filtering IS a form of EQ.

Since reading Mike Senior's book Mixing Secrets for the Small Studio http://www.cambridge-mt.com/MixingSecretsContents.htm I have been doing this on most or all of my tracks.

One of the purposes is to eliminate non-essential low frequency energy from the recorded sound. Examples: traffic rumble on a vocal track, body impact noise on a DI'ed acoustic-electric guitar. Low frequencies that aren't part of the musical sound per-Se.

A good way to dial it in is to insert an EQ with HPF capabilities, activate a HPF at the lowest available frequency, then gradually raise the frequency until you hear it adversely effecting the musical tonality of the track in question. Lower the frequency a bit from that point to give yourself a margin of error.

When you talk about keeping the keys out of the way of the guitar/kick out of the way of the bass it seems like a HPF would be too severe in most cases, although one with a VERY gentle slope could be useful. I think shelving or band filters would also be useful for that situation.

IMHO, of course!

[vvv]

That's a great book!

FWIW, I tend to HPF everything below 30-35Hz, except for (sometimes) kick. I have some default settings like where I HPF multiple electric rhythm guitar tracks at about 250Hz, etc., at least to start. I also frequently take the bottom off of backing vocals, sometimes from the lower mids.

Sometimes I usually use an FFT but sometimes a 12th order Butterworth (is that the name?) filter; the former is more gradual and "musical", the latter more extreme.

[Snarl 12/8]

I've always just used the eq's in my board or software for this. I'm guessing that's what most people use. My new board is digital, so the eq is very flexible. A lot of times just a slight shelf (3-6db) at a higher frequency (200Hz?) sounds better to me than a true "high pass" that's killing absolutely everything below what the cutoff is (say, 100Hz). Another fun thing to try is low shelf cutting 9db below 80Hz and then a big boost at 100Hz or something. (Frequencies and db's are totally arbitrary in what I'm saying, btw, since there's no actual track being eq'd.) That can do strange and wonderful things to your kick definition or what have you. Just get that thing out of the way and in the way in all the right places.

[vvv]

I've always just used the eq's in my board or software for this. I'm guessing that's what most people use. My new board is digital, so the eq is very flexible. A lot of times just a slight shelf (3-6db) at a higher frequency (200Hz?) sounds better to me than a true "high pass" that's killing absolutely everything below what the cutoff is (say, 100Hz). Another fun thing to try is low shelf cutting 9db below 80Hz and then a big boost at 100Hz or something. (Frequencies and db's are totally arbitrary in what I'm saying, btw, since there's no actual track being eq'd.) That can do strange and wonderful things to your kick definition or what have you. Just get that thing out of the way and in the way in all the right places.

Aminds me of how they say to use a Pultec ...

[kslight]

I almost always shelf or filter out unnecessary/conflicting content, if not when tracking then at least by the mixing stage.

[groover]

Aminds me of how they say to use a Pultec ...

Except that with the normal Pultec you can't set the cut and boost at different frequencies. But I have heard tell that some interesting things happen when you use the LF boost and cut together.
I can't hear it that well with my UAD plug-in version, but then my LF monitoring leaves something to be desired.

[GooberNumber9]

I actually HPF and LPF most of the tracks. I put them on and dial up the HPF until it starts to change the sound and then dial it back a bit, then the same thing with the LPF. I only sometimes HPF kick or bass, and I almost never LPF lead vocals or overheads/cymbals. Any track that needs to be highlighted and/or have some "air" will get no LPF or have it bypassed through automation at the appropriate time. Snare and guitars are likely candidates here. I will also often HPF and/or LPF reverb returns and mix them in just like any other track (I expect that's not so unusual since I picked up the practice from the community).

I imagine the HPFs and LPFs as basically being like a emergency vehicle lights for the tracks that NEED the highs or lows. Meaning, LPFing everything but lead vocals is basically saying "Lead vox gets priority above 12k, everyone else just has to get out of the way". That way I can guarantee presence (or thump) of (a) track(s) in the mix.

[ott0bot]

it kinda depends on the type of sound you are going for.

if you want a slick sounding, clean recording, then I hi and low pass the dickins of of some trAcks. especially the aforementioned guitars and various drum mics.

if I want a more live sounding, one room recording feel, definitely more or othe gentle boost and cut stuff.

like others said, I make alot of those discissions while tracking. for instance, micing a guitar can with a ribbon sometimes gives you a ton of bass from proximity effect that ill high pass to the point of need. field recording samples anywhere near a major road or freeway requires heavy filtering to keep the rumble at bay.

[Scodiddly]

As a live sound guy I couldn't live without them.

[cgarges]

Sometimes I use a hi-pass filter, sometimes I don't. Sometimes, I'll use a low-frequency roll-off on an EQ, as opposed to a hi-pass filter, because it often sounds different due to frequency selection, bandwidth, and/or circuit tone. Sometimes I'll do both if a source needs it. But if a source needs to be cleared up on the bottom, I usually listen to JUST the hi-pass first, as the simplest route.

Sometimes I'll use a hi-pass filter and boost low frequency stuff with an EQ, depending on the sound of the EQ. With an EQ that has a powerful bottom, sometimes just boosting even a little bit is too much, even though I might feel like a source needs some additional "heft" down there. In that case, boosting with the hi-pass engaged can be just the trick. That new AwTAC EQ is CRAZY good for this. The filter is set around a fairly high frequency, but with a gentle slope, so doing the boost/hi-pass thing really can give a source a nice, clear, full bottom end. Pultecs work in a similar fashion when boosting AND cutting on the bottom frequency. The bandwidth of the boost and cut control are different, so it can really give a shape to the bottom end. The Manley and Langevin versions of that EQ do the same thing. The classic API 550 series EQs will do this, but I find the effect much more subtle on those EQs.

Chris Garges
Charlotte, NC

[The Real MC]

Live or recording, HPFs are an underrated essential tool.

I find that crossovers make for good cheap effective HPF, LPF, or bandpass. Just put them in your inserts.

Between HPF and gating ringing toms/kicks, they really make a mix a lot better.

[drumsound]

I'll track with the hi-pass on the mic pre if I feel the need. My console has sweepable frequencies on all bands, so often when mixing I'm using the low shelf to cut things that get in the way and suck up headroom.

[Nick Sevilla]

I use filters all the time in mixing.

Especially on stuff that was recorded "flat" with no EQ nor compression.

You just have to get rid of the part of the frequency spectrum on a track, which you will never use.

This helps because the less unnecesary low end you have, the less muddy your mix, and the louder you can make your low end instruments, and similarly with the top end, the less of that unnecessary you have, the clearer the top end becomes.

A mentor of mine said it simply : "Focus".

When all you have are the things you need, you can make them work better in a mix.

Cheers

[telepathy]

I'll reiterate the "righteous/essential" position. especially being very specific with your chosen cutoff frequency. it sometimes helps to remember the key of the song & take notice of the part being played. I high-passed an electric guitar recently to remove mud (it was a hollowbody playing big chords, so there was a good amount of mud), which was successful except for one chord that didn't ring after the filter was engaged. it was an F, a barre chord in first position, and once I dialed back the filter to allow that F fundamental to come through, the guitar sounded huge without getting in the way of the real low-frequency information.