HPF vs. EQ

franvarin

franvarin

May 30, 2013
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#1
Hi everyone,
I have a curious question that I'm hoping someone can provide a clear explanation for. I've been researching the use of HPFs on live bass signal to eliminate sub-sonic noise. I believe I have a pretty good handle on the theory. But, where I'm confused is it seems to me I should be able to EQ that frequency out and eliminate it with a graphic eq...something like a Boss GEB-7. The latter has a band at 50hz so, is it possible to leave the other bands flat and just drive the one band all the way down to eliminate anything below 50hz in this case? If so, how does this differ from a HPF? Is it really the same thing?
 
#4
BadExample said:
HPF-Pre, updated December 18, 2016 - hpftechllc

I think you want a minimum 12db cut, more better. How much does the boss cut? Sealed or ported cab?
Click to expand...

As far as I remember the Boss bass Eq has a +/- 15 Db boost/cut pr. frequency.

The thing with graphic equalizers though is, as far as I understand it, please correct me if I got it wrong, that they only will cut the frequency you select to full extence of the cut selected and then a fairly narrow curve in the near perimeter to both sides, but since it's a curve not as much as the main frequency displayed and less and less the further you get from that frequency.

So if I am right it will work something like this: maybe cutting the 50 Hz band -15 Db, the 45 Hz band maybe -12 Db, the 40 Hz band maybe -6 Db and so on, and work the same way on the higher side of 50 Hz, 55 -12 Db, 60 -6 Db...

Mind these are only examples to illustrate how a graphic equalizer works and the curve (bandwidth) and cut might be even more narrow in reality.

So not the same effect at all, where a HPF would cut everything in a totally steep curve under a certain frequency.
 
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#5
NoiseNinja said:
As far as I remember the Boss bass Eq has a +/- 15 Db boost/cut pr. frequency.

The thing with graphic equalizers though is, as far as I understand it, please correct me if I got it wrong, that they only will cut the frequency you select to full extence of the cut selected and then a fairly narrow curve in the near perimeter to both sides, but since it's a curve not as much as the main frequency displayed and less and less the further you get from that frequency.

So if I am right it will work something like this: maybe cutting the 50 Hz band -15 Db, the 45 Hz band maybe -12 Db, the 40 Hz band maybe -6 Db and so on, and work the same way on the higher side of 50 Hz, 55 -12 Db, 60 -6 Db...

Mind these are only examples to illustrate how a graphic equalizer works and the curve (bandwidth) and cut might be even more narrow in reality.

So not the same effect at all, where a HPF would cut everything in a totally steep curve under a certain frequency.
Click to expand...

Most graphic EQ's notch a narrow frequency Q. So a little either side of that frequency and their effect is minimal. But many graphic EQ's last slider on the bass and treble side are shelving sliders. So every thing lower than that frequency (bass side) and everything higher (treble side) is effected. A bit like a B / M / T controls.
 
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#6
GMC said:
Most graphic EQ's notch a narrow frequency Q. So a little either side of that frequency and their effect is minimal. But many graphic EQ's last slider on the bass and treble side are shelving sliders. So every thing lower than that frequency (bass side) and everything higher (treble side) is effected. A bit like a B / M / T controls.
Click to expand...

Thank you for enlightening me in that aspect.

I know the following is not going to help OP, but your elaboration rise a question for me:

Would you happen to know if the last sliders on the graphic EQ on a Trace Elliot SM series would in fact also happen to work as shelving sliders or not?
 
#7
GMC said:
Most graphic EQ's notch a narrow frequency Q. So a little either side of that frequency and their effect is minimal. But many graphic EQ's last slider on the bass and treble side are shelving sliders. So every thing lower than that frequency (bass side) and everything higher (treble side) is effected. A bit like a B / M / T controls.
Click to expand...
So, if I follow all that's been said here about graphic EQs, each slider just controls the specific band they are assigned to. So, in the case of the Boss pedal I mentioned, the 50hz band (lowest and left most) would only have an effect on that specific frequency. So, anything lower (including the sub-sonic range I'm concerned with) would still flow through. Do I have this right?
 
#8
franvarin said:
So, if I follow all that's been said here about graphic EQs, each slider just controls the specific band they are assigned to. So, in the case of the Boss pedal I mentioned, the 50hz band (lowest and left most) would only have an effect on that specific frequency. So, anything lower (including the sub-sonic range I'm concerned with) would still flow through. Do I have this right?
Click to expand...
In simple terms, a HPF will start attenuating at the given frequency and roll-off everything below that point at whatever the filter is spec'ed for (usually given in dB/octave). Usually, graphic EQ filters are centered at the frequency you see on the slider and create a bell or inverted bell-shaped curve around that frequency (the width is referred to as its Q). It's possible (and I do not know in this case) that the top and bottom sliders will act as shelving filters affecting everything above and/or below the frequency shown.

If you want to dial out sub frequencies, your best approach IME is to use a HPF. The HPF-Pre Series 3 is excellent and very affordable for the quality, utility and flexibility/adjustability it offers.
 
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#9
Al Kraft said:
In simple terms, a HPF will start attenuating at the given frequency and roll-off everything below that point at whatever the filter is spec'ed for (usually given in dB/octave). Usually, graphic EQ filters are centered at the frequency you see on the slider and create a bell or inverted bell-shaped curve around that frequency (the width is referred to as its Q). It's possible (and I do not know in this case) that the top and bottom sliders will act as shelving filters affecting everything above and/or below the frequency shown.

If you want to dial out sub frequencies, your best approach IME is to use a HPF. The HPF-Pre Series 3 is excellent and very affordable for the quality, utility and flexibility/adjustability it offers.
Click to expand...

Here's a real world comparison (well, real models at least) of a 10 band graphic EQ with the lowest slider (32Hz in this case) pulled all the way down:

10Bandgraphic_32Hzcut.jpg


And a 4th order HPF set at -3dB = 32Hz:

HPF_32Hzminus3dB.jpg
 
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#11
Al Kraft said:
Your two pictures were easily worth more than 2000 words Charlie! :thumbsup:
Click to expand...

Well, there are many other different implementations of graphic EQs (and HPFs for that matter), but most of the ones I've seen with shelving on the lowest and/or highest sliders were in DAWs, and even then they are often lower order slopes.
 
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#12
Passinwind said:
Well, there are many other different implementations of graphic EQs (and HPFs for that matter), but most of the ones I've seen with shelving on the lowest and/or highest sliders were in DAWs, and even then they are often lower order slopes.
Click to expand...
My experience mirrors that, but I wasn't sure which graphic EQ the OP might end up using. My rule of thumb is that if you want to be sure you've got the sub frequencies taken care of, an HPF is the only way I know to be sure to get them all with a high level of attenuation.
 
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#13
So, with a graphic eq, a solid maybe :D My take:

With a ported speaker, it's more important to HPF. You want a sharp roll off somewhere above the port tuning freq. With a sealed speaker, you still save the energy wasted on freqs you can't hear or the speaker can't produce. Ported could get improved sound and safety. For a ported speaker, I would look closely at @fdecks HPF that cuts 12 db at a fixed freq. then cuts another 12 db at an adjustable freq. I don't recall the first stage cut freq., but he designed it to work with a 5 string. It would work for a sealed cab as well, but if the sealed cab is capable of going down below the cut off, it might be worth looking for something with a slightly lower cut off. With a ported cab, you may notice an improvement in clarity, but with sealed, not so much unless you were hitting xmax or encountering some other form of unwanted distortion without HPFing it. It all depends on what is coming out of your amp and what the cab is doing with it.
 
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#14
Al Kraft said:
In simple terms, a HPF will start attenuating at the given frequency and roll-off everything below that point at whatever the filter is spec'ed for (usually given in dB/octave). Usually, graphic EQ filters are centered at the frequency you see on the slider and create a bell or inverted bell-shaped curve around that frequency (the width is referred to as its Q). It's possible (and I do not know in this case) that the top and bottom sliders will act as shelving filters affecting everything above and/or below the frequency shown.

If you want to dial out sub frequencies, your best approach IME is to use a HPF. The HPF-Pre Series 3 is excellent and very affordable for the quality, utility and flexibility/adjustability it offers.
Click to expand...
Awesome explanation, thanks!
 
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#16
franvarin said:
Thanks! The graphs help a lot!
Click to expand...
Charlie always helps a lot! :D

For a ported cab, I think, you would want to shift the -3db cutoff on the HPF quite a bit to the right, depending on the porting. Probably 50 to 70 Hz if porting is unknown. I think some HPFs that are preset go higher than that. Take the advice of others on this if you are shopping by cutoff freq. This is just my gut feeling more or less.
 
#17
Passinwind said:
Here's a real world comparison (well, real models at least) of a 10 band graphic EQ with the lowest slider (32Hz in this case) pulled all the way down:

10Bandgraphic_32Hzcut.jpg


And a 4th order HPF set at -3dB = 32Hz:

HPF_32Hzminus3dB.jpg
Click to expand...

So the real difference comes down to the filter order. IIRC, 1st order is 3dB per octave, second is 6 and so on up to 4th at 12dB/octave, which is rarely found in graphic EQ pedals but we are saying is necessary, along with shelving vs bandpass. to function as a HPF?
So even if the bottom slider is shelving, if it is only 3 or at best 6dB per octave it will still not work as well as a dedicated 4th order filter? Makes sense to me.
 
#18
BadExample said:
Charlie always helps a lot! :D

For a ported cab, I think, you would want to shift the -3db cutoff on the HPF quite a bit to the right, depending on the porting. Probably 50 to 70 Hz if porting is unknown. I think some HPFs that are preset go higher than that. Take the advice of others on this if you are shopping by cutoff freq. This is just my gut feeling more or less.
Click to expand...

Say what?

Riis
 
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#19
Filter order + Q if it is a notch filter, as in a graphic eq.
Zooberwerx said:
Say what?

Riis
Click to expand...
I said: "For a ported cab, I think, you would want to shift the -3db cutoff on the HPF quite a bit to the right, depending on the porting. Probably 50 to 70 Hz if porting is unknown." and "Take the advice of others on this if you are shopping by cutoff freq. This is just my gut feeling more or less." :D

The idea is to not have much sound reproduced at the tuned freq. Most HPF's I've looked at have a higher -3db than 30 Hz.
 
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