High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread

[Al Kraft]

In the meantime ... there's lots of talk here about d-class amps (versus, presumably some other class, or versus all other classes). Now ... I have a vague understanding that the class of amp is due to the internal architecture of power transistors / power tubes (?) but I have no clue how that relates to the discussion of sub 40 Hz frequencies escaping from the amp into the speaker ... which is what this thread is all about right ?

So can someone please explain for me why the class of amp is relevant ?

Off the top of my head I would say the answer is tradition. Specifically, doesn't every thread that deals with some type of a problem/issue/concern end up eventually being an indictment of class D and SMPS technology?

 

[BadExample]

As an example, when you add one signal that is phase shifted exactly 180 degrees over part of it's range with a signal that is not phase shifted, you will get a subtraction of the larger signal from the smaller signal at that range. If the levels are the same, they will drop out entirely. There is a lot of phase shift with higher order active filters, sometimes not quite what you might expect.

Even worse than the 180 degree shift Andy probably used for simplicity is the 162.37 degree shift because you cant invert one signal to fix it.

Or maybe a 12 deg shift because it might not seem like a phase shift.

 

[BadExample]

sub 40 Hz frequencies escaping from the amp into the speaker ... which is what this thread is all about right ?

So can someone please explain for me why the class of amp is relevant ?

While your question has been answered, FYI and for those learning about filtering signals, you want to remove the deep bass before the heavy amplification, before the power amp section of you bass amp for sure. This conserves headroom.

I want to say furtest up the chain is best, but there may be cases where that doesn't work out so well. And I imagine a good quality bass amp has the HPF right where it's as effective as it needs to be.

 

[Sixgunn]

Then, yeah - the 800+ is definitely the way to go in your case, IMO... Nothing against the Quilter, but the D800+ is WAY more versatile - for a "one amp person", it's a no-brainer, IMO...

I respectfully disagree.

 

[RandM]

Yes, essentially identical to the D-800 preamp

Thankyou AH - PraiseB.

I know I'd experiment anyway and there was a single reference I think - if a HPF saves the amp from working with useless freqs'
we can't hear and improving performance - does it have a similar benefit for any pedals ect?

Where in the signal chain would it have the most benifit - or does that depend on personal taste/preference?

Cheers Maurie.

 

[BigBeatNut]

So can someone please explain for me why the class of amp is relevant ?

Thread drift.

Surely a query about why {Topic X} is relevant to the thread can't be considered thread drift ? Or did you mean that those mentioning d-class amps in the 1st place were guilty of thread drift ?

{EDIT} Of course this post, being a bit meta, might be considered thread drift

 

[Stumbo]

Thankyou AH - PraiseB.

I know I'd experiment anyway and there was a single reference I think - if a HPF saves the amp from working with useless freqs'
we can't hear and improving performance - does it have a similar benefit for any pedals ect?

Where in the signal chain would it have the most benifit - or does that depend on personal taste/preference?

Cheers Maurie.

There are benefits. The Effects Forum has some detailed threads on this topic.

 

[mesaplayer83]

I respectfully disagree.

You're certainly entitled to your opinion, but I think between the D800+'s EQ section, Voicing Knob, and variable HPF there's a pretty strong case made for my statement...

 

[NKBassman]

Thankyou AH - PraiseB.

I know I'd experiment anyway and there was a single reference I think - if a HPF saves the amp from working with useless freqs'
we can't hear and improving performance - does it have a similar benefit for any pedals ect?

Where in the signal chain would it have the most benifit - or does that depend on personal taste/preference?

Cheers Maurie.

As previously mentioned, I have used one at the beginning of my pedal chain before a compressor to filter out sub frequencies and prevent it from clamping down too hard. But most people would put it at the end of their pedal chain before the amplifier. Otherwise another good spot would be in the amp effects loop if the HPF can handle line-level signal.

 

[Bassist30]

I almost ALWAYS use a HPF on Acoustic instruments. Let's just say ALWAYS for acoustics.
Acoustic Guitars too. Nothing worse than a 6 string acoustic guitar Thumping deeper than a bass drum.. That's a MESS.

But Electric bass, I prefer to let it go AS IS, and just let the AMP that i select for that gig do the EQing .. Newer amps seem to all be pre HPF..
(edit) Its why still use my API 512 pre on some gigs. Its Fat, Wide and Fast... Or even my old 70s Alembic F2B that i have grown very fond of.. Not a great amount of EQ. BUT it has a synergetic beauty when used with a certain bass and cab..

Nothing like a F2B. Thanks for working on mine...... I can't think of a 3 knob pre better than that (on each channel). In fact very very few pre's match the Alembic F2B... Not sure what year is mine but they continue to make them the same.

 

[Sixgunn]

You're certainly entitled to your opinion, but I think between the D800+'s EQ section, Voicing Knob, and variable HPF there's a pretty strong case made for my statement...

You are entitled to your opinion also but saying it's a no brainer is a bit presumptuous. The D800 has a totally different EQ section. You prefer it which is fine and well. I prefer the EQ on the BB800. If I said it was better or a no brainer, that would be presumptuous on my part because I would be assuming everyone shared my tastes. As far as the HPF, the D800 has one but you're using a Fdeck, too. Kinda makes the added expense of the built in one sound like a waste of money, to me.

 

[PraiseBassing]

So would a passive 1st order HPF work in the effects loop of an amp with a line level effects send? I’d just enjoy the practice of making it and would probably make a couple with different cut-offs just because.

 

[Old Garage-Bander]

Surely a query about why {Topic X} is relevant to the thread can't be considered thread drift ? Or did you mean that those mentioning d-class amps in the 1st place were guilty of thread drift ?

{EDIT} Of course this post, being a bit meta, might be considered thread drift

Someone wanted an explanation about why X is in a thread about Y.
I gave one.
The requirement for it to be relevant to the relevancy was not related to me at the time.

 

[mesaplayer83]

You are entitled to your opinion also but saying it's a no brainer is a bit presumptuous. The D800 has a totally different EQ section. You prefer it which is fine and well. I prefer the EQ on the BB800. If I said it was better or a no brainer, that would be presumptuous on my part because I would be assuming everyone shared my tastes. As far as the HPF, the D800 has one but you're using a Fdeck, too. Kinda makes the added expense of the built in one sound like a waste of money, to me.

Where you're making your mistake here is that I specifically said the D800 PLUS - maybe you should go back and read what I posted again...

Also, using an fdeck with the D800 isn't "wasting" anything - it's merely bringing it's capability a little closer to that of the D800+...

I'll stick with what I posted earlier - the D800+ feature set makes it a no-brainer for a one amp choice... The Quilter is a nice amp, but is pretty primative when compared to the D800+ - not to mention Mesa's stellar reputation for reliability and customer service... I almost forgot - the Mesa's DI would be worth something, too...

 

[Downunderwonder]

I used to use an HPF when I played loud rock and had no PA support. And used crappy old cab technology. Then I moved into high-excursion drivers and the need lessened -- not totally -- but the speakers didn't flop radically the way old ones did. I especially needed it with small 8 inch drivers (hi excursion) driven at volume. Then my gigs became quieter without the need for big volume. So now I don't need an HPF. My comment was quasi-rhetorical, but maybe not? I think TalkBass people think about this stuff a lot more than the mass of bassists out there who only know they want to BOOST everything without understanding why.

There's an amazing emotional intensity in the remarks made in this thread. You'd think this HPF capability would be built into all bass gear. But it's not. My interpretation is there isn't enough general demand for such a simple application. The "need" is not felt as deeply by many as it is here. Ignorance is bliss I guess.

You can't so easily sell something to an ignorant bassist when it has a knob on it for cutting bass.

 

[agedhorse]

So would a passive 1st order HPF work in the effects loop of an amp with a line level effects send? I’d just enjoy the practice of making it and would probably make a couple with different cut-offs just because.

1st order tends to be intrusive on tone while offering minimal protection. Generally not all that helpful, unless you are looking to roll off audible low end.

 

[RandM]

Could an explanation of 1st, 2nd> ect order HPF's be given so creaky old halfwits
(me) can understand please? : )

 

[PraiseBassing]

1st order tends to be intrusive on tone while offering minimal protection. Generally not all that helpful, unless you are looking to roll off audible low end.

Well looks like I’ll look into something else for that then. Thank you @agedhorse!

 

[BigBeatNut]

Could an explanation of 1st, 2nd> ect order HPF's be given so creaky old halfwits
(me) can understand please? : )

A first order filter cuts at 6db/octave. ( e.g the signal at 10Hz is reduced by 6db more than the signal at 20Hz ). A 2nd order filter cuts off more sharply at 12db/octave, and 4th order filters 24 Db/octave are not unheard of. Anything more than that and it's getting like a brick wall cutoff. Below, blue = 1st, red = 2nd.

 

[agedhorse]

The reason it's called a first order is because of the math behind the filter that represents the slope of the rolloff.

All of the filters I design into bass amps are typically 4th order, or 24dB/octave (same as 80dB/decade)

The other parameter is called the alignment, it represents the shape of behavior as the filter begins to roll off. The quicker the transition, the more likely there will be ringing and artifacts, but if the transition isn't quick enough some of the effectiveness of the filter suffers. This is part of the art behind filters.