Using Parametric EQ as a Poor Man's HPF?

[agedhorse]

How many bass amps have you designed that don't already have a high pass filter like that internally?
Does adding a second external one really provide a significantly better outcome than using the tone controls?
Yes, technically it is different but really for practical purposes how much different?

Within the last 20 years, none.

With a fixed 24dB/octave HPF at 30Hz, it doesn't affect the low end tone at all (with a little subjectivity), and it works great for speaker protection.

With a variable HPF, sweeping up can allow much more precise control at say 50Hz while not affecting 55Hz - 60Hz appreciably. The same can not be said for tone controls.

For practical purposes, especially for those who may boost a little bass eq then roll off the very bottom of the boost, it can make a huge difference.

 

[crazyBassClown]

If I use the "low mid" control, when set to 50hz, and roll it completely off, could that possibly do the trick as an "on-board HPF"

For practical purposes, especially for those who may boost a little bass eq then roll off the very bottom of the boost, it can make a huge difference.

Well, how about in the actual case asked here, of using bass control, and then low mid set below it at 50Hz to roll the bottom of the low control off and then built in HPF? would that get fairly close to HPF with an adjustable cut off? To me it seems it really would, depsite ll the HPF love on here.

 

[Redbrangus]

That's because it is NOT shelving.

Except that a HPF absolutely is a shelving type filter. The attenuation RATE OF ROLLOFF remains constant, and when you integrate this the result is that the attenuation continues to increase the farther below the knee you get.

As expressed by @agedhorse is how I've always understood it.

 

[agedhorse]

Well, how about in the actual case asked here, of using bass control, and then low mid set below it at 50Hz to roll the bottom of the low control off and then built in HPF? would that get fairly close to HPF with an adjustable cut off? To me it seems it really would, depsite ll the HPF love on here.

Are you just being argumentative today or do you simply not understand?

It does not get even close because of the slopes are WAY too shallow to be effective. There's no way to get better than 6dB slope, which means that the signal is only 6dB down a full octave away from the knee. For a HPF, it's typically 18-24dB down, which means that you can lower the HPF to remove the energy that you don't want while minimizing the effect on energy that you do want.

Say you want the signal to be 24dB down at 20Hz, that would make the -3dB point 40hz with a 4th order HPF. For the same 24dB down using a first order tone control or eq, you would be 3dB down at 200Hz

Doing the same calculation with -24dB down at 25Hz would equate to -3dB at 50Hz with a HPF or -3dB at 250Hz with a tone control/eq.

THIS is why a HPF is a much more useful tool for this kind of signal processing.

 

[40Hz]

Does adding a second external one really provide a significantly better outcome than using the tone controls?
Yes, technically it is different but really for practical purposes how much different?

I can’t speak for every amp ever made. But running an SWR SM-400 with a HPF inserted in the effects loop (setting it around 50-60Hz if you’re also using a Goliath cab) makes a huge difference. You get cleaner punchier sound and you also significantly lower the amp’s running temperatures by using one.

There’s no settings on the limiter, the main EQ knobs, or the built-in semi-parametric graphic equalizer that will accomplish that on that amp.

 

[gitfiddl]

I can’t speak for every amp ever made. But running an SWR SM-400 with a HPF inserted in the effects loop (setting it around 50-60Hz if you’re also using a Goliath cab) makes a huge difference. You get cleaner punchier sound and you also significantly lower the amp’s running temperatures by using one.

There’s no settings on the limiter, the main EQ knobs, or the built-in semi-parametric graphic equalizer that will accomplish that on that amp.

My SM-400 is the reason I bought my HPF initially. I now use it with all my amps. It, for me at least, is truly one of those "How did I ever survive without it before?" tools.

 

[crazyBassClown]

Say you want the signal to be 24dB down at 20Hz, that would make the -3dB point 40hz with a 4th order HPF. For the same 24dB down using a first order tone control or eq, you would be 3dB down at 200Hz

Doing the same calculation with -24dB down at 25Hz would equate to -3dB at 50Hz with a HPF or -3dB at 250Hz with a tone control/eq.

THIS is why a HPF is a much more useful tool for this kind of signal processing.

Cool maths bro.
Now how about instead of a single theoretical filter, we go out into the real world, apply a 40hz HP filter 4th order, add on the bandpass eq -15dB at 50 hz. Then this real world response is much closer to 4th order HPF at 60-70Hz + 4th order HPF at 40Hz. Not the same but definitely getting in the ballpark. No one is asking you tot ake HPF out of amp, just pointing out that buying an additional hpf is probably not neccesary.

Since you are claiming expert status to back up your assertions, would you care to reconsider or defend this statement:

Except that a HPF absolutely is a shelving type filter.

Because wikipedia + any reference material I have ever read would disagree.
Insisting your word is gospel while making fundamental mistakes isn't exactly a good look.

 

[yodedude2]

key word there is 'type'. it can't be used to boost like a shelving filter; it is a specialized class of shelving type filter that only cuts, and in an more extreme fashion (usually). no mistake, and certainly no fundamental mistake, made in the statement.

 

[crazyBassClown]

key word there is 'type'. it can't be used to boost like a shelving filter; it is a specialized class of shelving type filter that only cuts, and in an more extreme fashion (usually). no mistake, and certainly no fundamental mistake, made in the statement.

Really? Unless you argument is all filters are shelving filters, which makes the statement pointless, then they are.
And even Aged knows the difference because his argument amounts to a bass control is a shelving filter and therefore doesn't continue to decrease output as frequency decreases, but "shelves" the decrease below a given frequency, hence the name.


High-pass and low-pass filters[edit]
A high-pass filter is a filter, an electronic circuit or device, that passes higher frequencies well but attenuates (cuts or decreases) lower frequency components. A low-pass filter passes low-frequency components of signals while attenuating higher frequencies. Some audiophiles use a low-pass filter in the signal chain before their subwoofer speaker enclosure, to ensure that only deep bass frequencies reach the subwoofer. In audio applications these are frequently termed "low cut" and "high cut" respectively, to emphasize their effect on the original signal. For instance, sometimes audio equipment will include a switch labeled "high cut" or described as a "hiss filter" (hiss being high-frequency noise). In the phonograph era, many stereos would include a switch to introduce a high-pass (low cut) filter, often called a "rumble filter", to eliminate infrasonic frequencies.

Shelving filter[edit]
While high and low pass filters are useful for removing unwanted signal above or below a set frequency, shelving filters can be used to reduce or increase signals above or below a set frequency.[13] Shelving filters are used as common tone controls (bass and treble) found in consumer audio equipment such as home stereos, and on guitar amplifiers and bass amplifiers. These implement a first order response and provide an adjustable boost or cut to frequencies above or lower than a certain point.

 

[Eighthnoterock]

I got one for myself for Christmas because I bought into the hype!?! Crap, I hate it when that happens.

 

[yodedude2]

Really? Unless you argument is all filters are shelving filters, which makes the statement pointless, then they are.

it's a 'type' of shelving filter in the way that it operates at a set frequency point instead of within a frequency bandwidth like some other filters can (edit: like the filters in a typical graphic e.q.). i'm sorry, i don't know how to explain it any more simply to you. good luck!

edit: this discussion reminds me of mccartney talking about how much he enjoyed the 'british eq' tone controls of the old abbey road mixing desks. he clearly described the effects of a shelving filter (both cutting and boosting) as opposed to a tone filter working within a fixed bandwidth.

 

[crazyBassClown]

it's a 'type' of shelving filter in the way that it operates at a set frequency point instead of within a frequency bandwidth like some other filters can. i'm sorry, i don't know how to explain it any more simply to you. good luck!

Shelving:

High and low pass

see how the "shelving" filter creates what looks like a shelf while the high and low pass continue to roll off forever. That is not a shelf, or shelving filter.

Whether you can explain it to me any more simply or not, what you are saying is simply incorrect.

 

[Al Kraft]

And most bass players ever haven't used a separate HPF, other than what their amp/cab provides.
Fiddling with low eq will probably get you most of the way and if you feel that isn't magical, a HPF probably won't be either.
I remember back in the day when the Bill Fitzmaurice cabs were the latest magical fad on TB. You don't tend to see them around here much any more, I guess the magic just fell out of em.
Or possibly things occasionally become over hyped in talkbass land

I can assure you as a musician and an engineer (over 40 years experience in both fields) that "fiddling with the low EQ" will not get you what you can get with a HPF (unless it is actually a HPF and mislabeled as a low EQ). There is no magic involved there and filter (shelving EQ, peaking EQ, high pass, low pass, band pass, etc.) designs are anything but a fad. Although I think most engineers would admit that implementing filters in a musical and useful way does involve a touch of both art and science.

I don't think Bill Fitzmaurice products or their/his lack of presence here today had anything to do with lost magic either. Bill had a style of communication and lack of patience for self-proclaimed experts in his area of expertise that I suspect were prime reasons for his current absence, but to the best of my knowledge his products continue to perform as designed.

While some things on TB may be overly-hyped at times, I tend to see enthusiasm over innovative/novel designs as natural in an amps and cabs forum. While the HPF is neither innovative nor novel in electronics, some of the newer implementations that provide speaker protection, preserve headroom, and can be used in a variable, complementary way with an amp's tone controls are worth a little hype IMO. At least for me, compared to amps with no HPF or a fixed HPF it is a bit of a game changer. YMMV of course.

 

[40Hz]

Since you are claiming expert status

He is an expert, bro. He doesn’t need to claim he is.

Apparently you have absolutely no idea who he is or what he does.

Mind sharing your electronics and technical credentials with us so we can have a better idea who you might be?

 

[crazyBassClown]

He is an expert, bro.

Apparently you have absolutely no idea who he is.

Actually I do know who he is, and yes he is an expert. He is also not god.

He is also factually challenged about fundamental terminology in this instance.

Bill had a style of communication and lack of patience for self-proclaimed experts in his area of expertise that I suspect were prime reasons for his current absence

BFM's problem was with anyone who dared question any single statement he had to make. I remember much heated discussion a long time ago where he absolutely insisted that there was absolutely no point at all in adding a crossover to piezo tweeters because it was not required and made absolutely no difference. As was commanded by god, or something.
Low and behold a while later, crossovers suddenly appeared within his designs. I guess he finally realised he may not know absolutely everything and other people may know something as well.

IF you want to share knowledge being prepared to teach and justify your position is helpful. Merely saying "this is so" tends to rub people the wrong way when most things aren't actually absolute.



I also remember when markbass was "THE" thing to get, now moved on to darkglass. probably end up being something else next.
Are all these things good? Yes, including HPF.
But it's not some magic talisman that absolutely everybody needs and a counter opinion to the hypers may help people avoid dissapointment when the HPF isn't the absolute be all end all they think it's going to be.
People have managed to get by just fine without em for a long time.

 

[Redbrangus]

In reference to filters, I've always used the term 'shelving' to distinguish that filter shape from a 'peaking-dipping' or bell-shaped one. In that context, I have always considered a HPF to be a specialized, multi-pole, shelving-type filter. I wasn't even aware that there are filters with the response curve described, where the response is constant below the corner frequency...I had always assumed that the response continued to decrease as the frequency decreases, even in simple filters. But obviously I'm not much of a filter guy...I build speakers and play a little bass guitar.

 

[agedhorse]

Cool maths bro.
Now how about instead of a single theoretical filter, we go out into the real world, apply a 40hz HP filter 4th order, add on the bandpass eq -15dB at 50 hz. Then this real world response is much closer to 4th order HPF at 60-70Hz + 4th order HPF at 40Hz. Not the same but definitely getting in the ballpark. No one is asking you tot ake HPF out of amp, just pointing out that buying an additional hpf is probably not neccesary.

Since you are claiming expert status to back up your assertions, would you care to reconsider or defend this statement:


Because wikipedia + any reference material I have ever read would disagree.
Insisting your word is gospel while making fundamental mistakes isn't exactly a good look.

No, it's not the same, similar, or even close. The -15dB bandpass at 50Hz will have a -3dB point at around 200Hz. Bandpass filters in typical eq stages are also first order filters unless you add gobs of feedback to greatly increase the Q, but that doesn't work well for tone control purposes so it's not often done.

Regarding filter shapes, there are peak dip type filters (also called bandpass/band reject filters or bell shaped filters) and there are shelving type filters, that's about it for audio. I don't care what somebody in the audiophile community calls something, these are the same folks that believe electrons can only travel one direction in a wire (the electrical equivalent of "the earth is flat")

Baxandall type filters are just a form of shelving filter.

I don't need to justify what I learned in my 6 years of engineering education. Your posts are becoming more confrontational and less respectful, I don't think this is appreciated by anyone here.

 

[40Hz]

Actually I do know who he is, and yes he is an expert. He is also not god.

He is also factually challenged about fundamental terminology in this instance.

Uh-huh. Now about your credentials?

 

[Al Kraft]

Actually I do know who he is, and yes he is an expert. He is also not god.

True, but it wouldn't surprise many of us to find that god has him on speed dial for times when difficult amplifier design questions come up.

People have managed to get by just fine without em for a long time.

I'll agree that people have managed to get by, but is that the same as getting the most out of their amp/cabs? I will be the third SWR SM-400 owner in this post who will tell you that a HPF used with that head makes a night and day difference. While my SM-400S managed to work okay before I used a variable HPF, it did much more than just manage to do a good job with one. To your point though, some heads already have a suitable HPF and more of a good thing doesn't necessarily/automatically become additive in win column IME.

 

[PraiseBassing]

Where is the logic in using 3 filters to accomplish the job of one appropriately designed one?