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Heads with built in high pass filters


BillyBass

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3 minutes ago, Downunderwonder said:

Yup, I must have got my eyes crossed looking at it on my phone!

 

For the continued mystified:

 

Placing a straight edge on the graph at 0dB& 40hz, parallel to the gist of the intial curve, hits 10hz down at -36dB = 18dB per octave. [10¹ hz to 40hz is 2 octaves]

18db/octave is logical as that can be done with one opamp. 24db/Oct needs 2 opamps so a budget-oriented design is more likely to be 18.

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5 minutes ago, Al Krow said:

Haha - we maybe need @Chienmortbb to put us out of our misery and share what he thinks the slope is! 

 

The Veyron is certainly an amazing value bit of kit and if it's delivering 18dB/octave cut below 30Hz, well that works for me.

My adjustable 24dB / octave filter moves between 50hz and 80hz depending on room and genre and rig.

 

Sometimes the bass EQ gets a bit of a boost along with the filter shifting up. It is great having the EQ liberated from mud control.

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2 hours ago, NHM said:

 

Is it more effective to put a HPF first in the chain, or last, (such as in the amp's effects loop)?

Depends on what fx you have and how you like them. Also depends on if you are being fed to PA and you like some reins on soundguys that would be better pint pullers. Also the signal level in your fx loop and what your HPF likes.

 

A few examples.

 

Compressors and envelopes and octaves sometimes need the whole enchilada signal to do their best work.

 

An octave down will need HPF to follow in any case.

 

If your DI comes from a pedal you'll want the HPF in before that unit.

 

If you don't have any pedals and your HPF is a line level operating unit you'll want it in the fx loop.

 

Sometimes a unit will be good in a pedal loop with the buffered signal but too little input impedance of its own to plug pickups in direct.

 

Some big gun little stage players go the other direction and put HPF after their FOH send so they can make the stage amp bark a bit louder without sending a whole lot of lows into the room that messes up FOH.

 

 

 

Edited by Downunderwonder
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2 hours ago, NHM said:

 

Is it more effective to put a HPF first in the chain, or last, (such as in the amp's effects loop)?

Max at SFX Sound recommended it should be the first thing in the chain. If the effects loop is parallel, as many are, some LF will still get through, so caveat emptor.

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15 minutes ago, pete.young said:

Max at SFX Sound recommended it should be the first thing in the chain. If the effects loop is parallel, as many are, some LF will still get through, so caveat emptor.

I think I agree with Max, adding the HPF early in the chain increases headroom at each stage.

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thanks for the helpful advice about where best to place the HPF. I've been running mine in the effects loop so I'll switch it around to come after the compressor - it will be interesting to hear the difference.

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22 hours ago, Downunderwonder said:

Some big gun little stage players go the other direction and put HPF after their FOH send so they can make the stage amp bark a bit louder without sending a whole lot of lows into the room that messes up FOH.

I'm more 'derringer' than 'big gun' but that's exactly what I do when there's an external soundman. Give them everything, keep the sub bass off the stage. Why knows what they'll be needing for the room (or more likely field as we only really work with sound crews outdoors) and it's near impossible to get that sub bass back after it's been so well removed. 

 

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3 hours ago, NHM said:

thanks for the helpful advice about where best to place the HPF. I've been running mine in the effects loop so I'll switch it around to come after the compressor - it will be interesting to hear the difference.

I would place it before the compressor. That way the detector won’t key off of the low stuff you are filtering out.

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On 22/11/2021 at 10:35, NHM said:

 

Is it more effective to put a HPF first in the chain, or last, (such as in the amp's effects loop)?

I guess our man Down under has it sussed. Sounds pretty sensible... 

 

I don't use a lot of peripheral gadgetry, I tend draw straight lines from points A to B if I can. Mostly I'm looking to keep inaudible lows out of my system.

In any sort of modern pa there's a lo-pass toggle on the channel my DI goes to, so there's an argument you can make for patching it into my fx loop. 

But I'm starting to 'check out' now as I begin thinking about it... I'm going to sit down... 😆

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On 11/11/2021 at 08:50, Downunderwonder said:

My adjustable 24dB / octave filter moves between 50hz and 80hz depending on room and genre and rig.

 

Sometimes the bass EQ gets a bit of a boost along with the filter shifting up. It is great having the EQ liberated from mud control.

 

Indeed, that can be a nice 'trick': bump the bass EQ a bit, and then turn up the filter cutoff frequency removing the lowest lows until... well, until it sounds right. It allows you to get a nice and fat low end without the mud. I 'discovered' that by chance, using the Mesa D800+'s built-in adjustable HPF. I thought I was so clever... then I saw I had just invented the wheel a few thousand years after the original :D

 

 

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On 07/11/2021 at 12:41, Al Krow said:

 

I put the question to sfx who make the Thumpinators back in 2019 and received this response which was instructive:  "I do not publish the slope of the micro-Thumpinator filter. The only thing I can tell you is that the micro-Thumpinator cuts at more than 12 dB/oct." All the best, Max [sfx]

Phil's charts in the post above really do demonstrate how effective it is in reducing unnecessary speaker excursion in the sub-audio range. Be interesting to know if any amp's HPF are comparably good? My guess is that a few may be, particularly where they are an advertised feature, but many are not given the additional component cost etc.

Perhaps worth pointing out that it's not either / or - a Thumpinator in series with the amp's HPF should work in tandem to eliminate unwanted low end.

I do like where the Thumpinator cut-off is set i.e. just below the low B fundamental on a 5 string. Perfect for us 5 string players - although I appreciate we're going to be much more focussed on the 1st and 2nd harmonics, it's nice to know that the fundamental is still in there!

 

 

On 08/11/2021 at 08:44, pete.young said:

 Interesting that, I'm sure when we've talked about this in the past a figure of 24dB/oct has been bandied about. I don't recall whether there was any evidence to back this up. Maybe someone on Talkbass tested it?

 

Just had a little catch up with Max and he's pointed out that he's had the spec for the Thumpinator up for the past 12 months or so:

  • Cut-off frequency: ~25Hz
  • Slope: 36 dB/oct

Good to finally put the record straight on that. That's pretty steep and explains why it's such an effective tool for eliminating low end crud! He also confirmed that the only the layout had changed between the Mk1 and Mk2 versions i.e. the slope and cut/off remained the same.

He was also interested to hear about this little offering from Zorg, which he'd not come across previously. 

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I had a QSC PLX1202 power amp. It had dip-switches for an HPF ( on/off, 35Hz/50Hz -3dB 24dB/ octave roll-off)

 

This afforded me the opportunity to experiment. The 35Hz setting helped a lot. Cleared out a lot of "congestion" from the sound,  and audibly decreased the stress in the sound from the cabinet, while also tangibly increasing headroom. 

I was reluctant to use the 50Hz setting,  as it's below the fundamental of even "E" (about 41Hz). Turned out it was even better,  despite supposedly being above the lowest frequency the cab could supposedly output (but no dB reference point was given!)

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The obvious benefits of an HPF have interested me for awhile.

 

A few years ago I borrowed a Thumpinator and used it with an Aguilar TH500 through 2 Berg AE112's. I noticed very little difference with and without. I didn't see any change in the movement of the cones.

 

At the moment I'm running a Berg Forte HP through a Super Compact and sometimes with a Super Midget as well, and I still don't hear the HPF making much of a difference. The point where I can hear the HPF working it's changing the tone in a very unpleasant way, making it thin and nasty.

 

Is the HPF doing its job when I can't hear it? How do I know if it's doing anything useful not?

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27 minutes ago, chris_b said:

The point where I can hear the HPF working it's changing the tone in a very unpleasant way, making it thin and nasty.

You've got the idea then. Backing it off until it sounds good again is a great way to get set.

 

Should you crank something else up you won't be sending wobbly distortion. If you hear wobbly distortion or an excess of low end you can up the HPF a tad.

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27 minutes ago, Downunderwonder said:

You've got the idea then. Backing it off until it sounds good again is a great way to get set.

 

Should you crank something else up you won't be sending wobbly distortion. If you hear wobbly distortion or an excess of low end you can up the HPF a tad.

 

I get that, but am I to assume that the HPF is working? How do I tell if I can't hear or see any changes?

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24 minutes ago, chris_b said:

 

I get that, but am I to assume that the HPF is working? How do I tell if I can't hear or see any changes?

Eat your vegetables!

 

I'd say your cab probably rolls off in response right where you are comfortable so you don't hear any difference. That's fine until push comes to shove and bit more trim comes in handy, either to save the speakers or right the tone. Our ears gain low end sensitivity at higher relative volumes.

 

Or you might get a different gig where a deep blue sea of low end fundamental isn't what's wanted.

 

A good experiment is to set up with the HPF off and the right amount of bass EQ. Then put in a little too much bass EQ but now bring up the HPF.

 

That's often a different kind of good when you have limited EQ control. Not sure you don't have parametric filters up the wazoo on your flash amp though.

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5 hours ago, Lfalex v1.1 said:

I was reluctant to use the 50Hz setting,  as it's below the fundamental of even "E" (about 41Hz). Turned out it was even better,  despite supposedly being above the lowest frequency the cab could supposedly output (but no dB reference point was given!)

Most of your sound's "very-lows" are harmonic anyway. 50Hz isn't actually very useful, contributing to Sonic 'mud' for your FOH person to wrassle with, and that's not good for you. 

In a live mix those lows contribute pretty much nothing musically: they're hard to discern, they beat up your speakers, and take a lot of your amp's power (headroom) to reproduce. This is what the HPF is good for dealing with. Don't think of it as totally eliminating them, it's more like it discourages them. 

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