Jump to content
funkydoug

High Pass Filters

Recommended Posts

3 hours ago, Jus Lukin said:

Just on the PEQ- it won't actually be acting as a high pass filter. While it's removing the demanding frequencies which are causing air movement, it is only cutting around the set frequency. A high pass cuts progressively as you head downwards from the set frequency, ie,  if you have -24db/oct at 30hz, signals at 15hz will be attenuated by 24db, signals at 7.5hz will be attenuated by 36db, 3.75hz will down by 48db, and so on. The PEQ is actually a notch filter set low, and while it may be cutting a lot at 30hz it may well be leaving 7.5hz untouched.

Just being pedantic, but it's worth doing so when we are using specific terms! They could both be called a low cut, but a high pass and a notch are different things. 

So based on Al Krow experience should I setup three PEQ patches in series set at 20Hz, 15Hz and 7.5Hz ? Would that over lap work as a HPF Set at 39Hz as per my Thumpinator?

Should the Q value be set at the mid point?

Share this post


Link to post
Share on other sites
22 hours ago, JohnDaBass said:

So based on Al Krow experience should I setup three PEQ patches in series set at 20Hz, 15Hz and 7.5Hz ? Would that over lap work as a HPF Set at 39Hz as per my Thumpinator?

Should the Q value be set at the mid point?

Hi - on the Zoom B3n the lowest PEQ centre setting is 20Hz. Going up from that, the next two were 25Hz and 32Hz, but I found that 32Hz and above was impacting on tone. So you could cut at 20Hz and 25Hz (plus, if you want, an extra one to double up the cut at 20Hz) sounds like a good combination. 

I thought the Thumpinator was set at 28Hz? But I am more likely than you can to be wrong on this, as I don't have one! 

Q values - as I mentioned, I found there was a trade off between tone (better at high Q) and effectiveness of cut (better at low Q) hence going for a mid point, but others may have further insight on this. 

Edited by Al Krow

Share this post


Link to post
Share on other sites
12 hours ago, Jus Lukin said:

Just on the PEQ- it won't actually be acting as a high pass filter. While it's removing the demanding frequencies which are causing air movement, it is only cutting around the set frequency. A high pass cuts progressively as you head downwards from the set frequency, ie,  if you have -24db/oct at 30hz, signals at 15hz will be attenuated by 24db, signals at 7.5hz will be attenuated by 36db, 3.75hz will down by 48db, and so on. The PEQ is actually a notch filter set low, and while it may be cutting a lot at 30hz it may well be leaving 7.5hz untouched.

Just being pedantic, but it's worth doing so when we are using specific terms! They could both be called a low cut, but a high pass and a notch are different things. 

Just querying one point, if I may: - the typical HPFs available (e.g the Broughton) cut by 12dB (which one of our experts has remarked as being insufficient), so -12dB would seem to me to be the maximum attenuation? If that is correct, then your "-24db/octave" attenuation figures would, in practice, be much smaller and HPFs typically not deliver a cut of up to 48dB at 3.75Hz etc? 

Share this post


Link to post
Share on other sites
7 hours ago, Al Krow said:

Just querying one point, if I may: - the typical HPFs available (e.g the Broughton) cut by 12dB (which one of our experts has remarked as being insufficient), so -12dB would seem to me to be the maximum attenuation? If that is correct, then your "-24db/octave" attenuation figures would, in practice, be much smaller and HPFs typically not deliver a cut of up to 48dB at 3.75Hz etc? 

No not maximum attenuation. -12dB per Octave. Every time you drop an octave (half the frequency) you're another 12dB down. Take the example of a -12dB/Octave HPF with a cutoff frequency of 200Hz (obviously high for bass guitar use, but just for illustration). At 100Hz the filter is cutting 12dB, at 50Hz it's cutting 24dB, at 25Hz it's cutting 36dB, and so on.

  • Thanks 1

Share this post


Link to post
Share on other sites
42 minutes ago, Bigwan said:

No not maximum attenuation. -12dB per Octave. Every time you drop an octave (half the frequency) you're another 12dB down. Take the example of a -12dB/Octave HPF with a cutoff frequency of 200Hz (obviously high for bass guitar use, but just for illustration). At 100Hz the filter is cutting 12dB, at 50Hz it's cutting 24dB, at 25Hz it's cutting 36dB, and so on.

Ok thanks to you and @Jus Lukin for clarifying this.

Seems to me that -12dB / octave on an HPF is pretty steep (and is very different to what a PEQ will be doing).

Could I be so bold then and just query whether an HPF really needs -24dB / octave (per @Chienmortbb's excellent earlier post)?

Share this post


Link to post
Share on other sites

It's only taken 11 pages... O.o

Different strokes for different folks I suppose! For a hard cutoff HPF like the Thumpinator, then 24dB is certainly more appropriate. For speaker sim 12dB is better, but might still be a little harsh for some applications.

Share this post


Link to post
Share on other sites
18 hours ago, JohnDaBass said:

So based on Al Krow experience should I setup three PEQ patches in series set at 20Hz, 15Hz and 7.5Hz ? Would that over lap work as a HPF Set at 39Hz as per my Thumpinator?

Should the Q value be set at the mid point?

Well... no!

I've pinched a picture off Google, which shows the two types of filters on a graph. The HPF (top right) starts at a certain point and just keeps on cutting. The band reject (although you can see why it's also called a notch, bottom right) cuts around the set frequency  From the point of view of high pass filtering, the high pass only let's the highs pass the set frequency. The notch, as on the PEQ cuts around the frequency, but still lets lows pass the filter.

fig1.jpg.36654f82952036fda57e5fb119bdb017.jpg

The Q is simply the width of the notch, so can't be set any way other than at the mid point. It always varies the breadth of the notch around the mid point, which is more commonly called the centre frequency, or set frequency.

Share this post


Link to post
Share on other sites
19 minutes ago, Bigwan said:

It's only taken 11 pages... O.o

Different strokes for different folks I suppose! For a hard cutoff HPF like the Thumpinator, then 24dB is certainly more appropriate. For speaker sim 12dB is better, but might still be a little harsh for some applications.

Haha - some of us are more simple bass players than electronics whiz kids. But nonetheless have a willingness to learn (and bear in mind the lower elasticity of our grey matter corresponding to the greyness of our hair...)

Share this post


Link to post
Share on other sites
Guest adi77

Q determines how narrow or wide the bell is :)

Share this post


Link to post
Share on other sites
49 minutes ago, Al Krow said:

Ok thanks to you and @Jus Lukin for clarifying this.

Seems to me that -12dB / octave on an HPF is pretty steep (and is very different to what a PEQ will be doing).

Could I be so bold then and just query whether an HPF really needs -24dB / octave (per @Chienmortbb's excellent earlier post)?

As Bigwan says, different strokes, or rather, it depends what the application is. In physical electronics, the basic high or low pass filter is 6db/oct, I presume just by nature of the components. Higher cuts are usually just stacked versions of these, although the digital realm is no doubt much different.

The simplest way to look at it is that a steeper slope will be more audible, a shallower slope more natural sounding. For an HPF, potentially, the lower you set it, the steeper you want it to be, as it will be harder to hear down there, but you want it to be effective by the point of subsonics. The Thumpinator is a good example if this, leaving 30hz untouched, but cutting quite hard below there. Speaker sim is also a good example, where an old school sealed cab will naturally begin to roll off low end quite high, but with a gentler slope, where 6 or 12db/oct might give a similer effect.

Of course it gets much more complicated. There is not only the slope, but the curve- the cutoff frequency is usually where the signal is already down by 3db, and there a numerous different curves. I'd need to look them up to be specific, but off the top of my head the Bessel is the simplest curve, a fairly straight angle on a graph, but which also has resonance at the cutoff, another feature of filters which means there is also a boost at the cutoff frequency! The most popular for crossovers, both for the HPF and LPF is the Linkwitz-Riley curve, which is not resonant and combines into a flat response between high and low bands when set to the same frequency, regardless of slope.

If you're really interested, it might be worth having a nerd up session, reading from the point of view of sound engineers or electronics engineers rather than just bass use. You don't have to be an expert (I'm far from that myself) but it will give you a much more complete picture, and will probably be more comprehensive and informative overall than us lot! xD

Share this post


Link to post
Share on other sites
30 minutes ago, Jus Lukin said:

The Q is simply the width of the notch, so can't be set any way other than at the mid point. It always varies the breadth of the notch around the mid point, which is more commonly called the centre frequency, or set frequency.

Agreed. I think what @JohnDaBass was getting at was should Q be at the mid point of the available breadth range for it i.e. 0 to 16 on Zoom. As that range is non linear, 4 is actually the mid point on the patch 'dial'. I've set out why I found a mid point 4 range to be best when I was using.

Share this post


Link to post
Share on other sites

Ah, I see! Well, there is no should- the ears and/or situation need to be the judge.

Share this post


Link to post
Share on other sites
9 minutes ago, Jus Lukin said:

Ah, I see! Well, there is no should- the ears and/or situation need to be the judge.

My conclusion exactly, too :) 

Share this post


Link to post
Share on other sites

I play in a function band and a Pub rock band. The function band demands quite a wide variety of bass sounds and to deliver those sounds I have  created a very flexible pedal board. I wish to create a much smaller pedal board for the Pub rock band. I want to use my "new" Zoom MS-60B to provide and replace a tuner, Thumpinator and TC Spectra Comp and then into my Tech21 VT Bass DI. So I end up with two pedal boards.

So the main reason for being so inquisitive ( Pain-in-the-Backside) is to grasp whether the PEQ on the MS-60B can get close to what the Thumpinator is doing. So my current understanding is that I should set up two or three PEQ in series with the frequency set at 25Hz & 20Hz with Q set at around 4. This would give a " notch" centered at 25hz & 20Hz and the Q of 4 would produce a notch width of (maybe?)+ 10Hz - 10Hz . I would in effect being cutting frequencies from 10Hz to 35Hz. As Al Krow correctly pointed out to me the Thumpinator is set to 30Hz  so I am possibly 5Hz higher.

The rest of my rig is a Mesa Subway D800 and one or two Barefaced Super Compacts. The reason for the Bright Onions switch is to allow me to feed my bass signal into the front of the Mesa D800 via the BD I21 ( for boost mid song) and the Tech21 VT Bass DI Deluxe into the AUX in of the Amp. The Mesa D800 has a fixed HPF in the preamp which is why I only use the Thumpinator after the BO Switch and into the Tech 21 VT Bass Deluxe then into the AUX IN of the Amp. The Aux In signal is inserted before the Master Volume control so it is simple to balance my sound between the Mesa Preamp and the VT Bass DI Deluxe. The setup enables me to have seven ( plus boost) pre set analogue sounds all accessed via the footswitches. I know it's NOT a HELIX but it really suits my needs.

Sorry for the long explanation but I just wanted to get my dumb questions into some sort of context for the "Clever Ones" amongst us who help so much in broadening our understanding of what we are all trying to achieve.

20180403_134838.jpg

Share this post


Link to post
Share on other sites

Sounds like a great setup!

The HPF in the MS-60b is to be found in the AcBsPre, which is based on the Fishman Platinum Pro EQ. The 'depth' control is for the filter, 10 being minimum cut. Depending how accurate the copy of the filter it is, it should be introducing a cut at 10hz even at 10. At 9 it is cutting from about 40hz, so is the most akin to a Thumpinator. We also discussed stacking these filters to get a steeper slope, which reminds me- I need to download the bit of software which was kindly used earlier on to test the filters and do my own experiments! I find that with the AcBsPre, all EQ halfway with Gain at 50 and Level at 100 gives me a 'bypassed' sound which I can use as just a low pass filter.

Using notches will to some degree or other leave 'unwanted' VLF content, so not perform speaker protection well, or stop VLF hitting compressors or overdrives and having an effect on tone/response. Whether something like 5hz is actually present in a bass guitar signal at all, or in quantity to cause issue is not somethig I can say for sure, but if it is, notches will be doing little or nothing to attenuate that signal. A HPF will.

For the uses you mention, the comps in the Zoom are fine, and there is also a Sansamp Bass Driver sim, or SVT sim, so you may find you can get away with just the one box. I've used mine as HPF-Comp-Overdrive Pedal-SVT for classic rock gigs to good effect, and will again!

Please don't consider your questions a pain in the bum- or consider many of us clever! ;) I'm just an obsessive nerd about this stuff. xD

Share this post


Link to post
Share on other sites
On 23/02/2018 at 17:25, Al Krow said:

These are the specs I have provisionally agreed a couple of weeks back with Tom at COG.

  1. Fixed HPF with 12dB cut at 28 Hz
  2. Variable 12dB cut at HPF 20Hz to 400Hz (to deliver the desired 24dB HPF cut at 28Hz and below with a combination of the fixed and variable HPF)
  3. Variable LPF 12dB cut at 700Hz to 14kHz 
  4. Two true bypass switches: one for the two HPF filters, a second one for the single LPF filter; and
  5. Volume control to add +20db (to compensate, if required, for the effect of the cut being caused by engaging the filters)

With the unit housed in a 1590BS (11.2cm x 6.0cm x 3.8cm)

... although I've had radio silence for a couple of weeks from Tom which is always a little frustrating, but I guess he's busy.

What do folk think about the spec? Any other folks interested in getting something like this?

@Bigwan - something you could put together? If so, please PM me with your thoughts on pricing (I can't be doing with waiting for Tom to get back to me forever :) )

I’ve been thinking about getting a HPF. I use the one on my B3n for my bass guitar and the deep control on my fishman for my double bass. I do like the idea of having one separate from the B3n as I don’t always have room for it in a patch and also feel I’d rather have it a bit more hands on. I’d thought about getting in touch with Tom to make a version of the fDeck but would be interested in the hpf +lpf.

Share this post


Link to post
Share on other sites
8 minutes ago, Apeneck Sweeney said:

I’ve been thinking about getting a HPF. I use the one on my B3n for my bass guitar and the deep control on my fishman for my double bass. I do like the idea of having one separate from the B3n as I don’t always have room for it in a patch and also feel I’d rather have it a bit more hands on. I’d thought about getting in touch with Tom to make a version of the fDeck but would be interested in the hpf +lpf.

Feel free to PM me and I'd be happy to share where things have got to with the above.

Share this post


Link to post
Share on other sites
On 4/3/2018 at 06:38, JohnDaBass said:

So the main reason for being so inquisitive ( Pain-in-the-Backside) is to grasp whether the PEQ on the MS-60B can get close to what the Thumpinator is doing. So my current understanding is that I should set up two or three PEQ in series with the frequency set at 25Hz & 20Hz with Q set at around 4. This would give a " notch" centered at 25hz & 20Hz and the Q of 4 would produce a notch width of (maybe?)+ 10Hz - 10Hz . I would in effect being cutting frequencies from 10Hz to 35Hz. As Al Krow correctly pointed out to me the Thumpinator is set to 30Hz  so I am possibly 5Hz higher.

 

The best way to figure this out for real is to simply measure it yourself. If you have even a rudimentary soundcard there are plenty of freeware solutions to doing that. Several years ago a friend on another forum asked why just cutting his ten band EQ pedal at 32 Hz wouldn't work just as well as using a dedicated HPF. So here's roughly what a 10dB cut at 32Hz would look like:

10Bandgraphic_32Hzcut.JPG

 

...compared to a fixed 12dB + variable12dB format HPF set for a -3dB point of 32Hz:

 

HPF_32Hzminus3dB.JPG

 

Note that especially in at least the first case whatever native low rolloffs the rest of the system provide could impact the left side of that curve quite substantially. Hence my recommendation to actually measure rather than assuming. Yel_wink.gif

Edited by Passinwind

Share this post


Link to post
Share on other sites

Time to call in the cavalry!

@bartelby Hey buddy would you mind setting up a patch on your B3 with 3 PEQ effects, two centred at the lowest 20Hz setting and one a notch higher at 25 Hz? All three with Q=4 and maximum cut "-20" and posting what that looks like compared to clean by-pass please?

Edited by Al Krow
  • Like 1

Share this post


Link to post
Share on other sites
55 minutes ago, Al Krow said:

Time to call in the cavalry!

@bartelby Hey buddy would you mind setting up a patch on your B3 with 3 PEQ effects, two centred at the lowest 20Hz setting and one a notch higher at 25 Hz? All three with Q=4 and maximum cut "-20" and posting what that looks like compared to clean by-pass please?

on the B3 PEQ there are two sweepable EQ's per effect so it would be possible to do 6 PEQ effects, completely over the top though, I think the law of diminishing returns kicks

 

Edited by PaulWarning

Share this post


Link to post
Share on other sites
Guest adi77

Does anybody still makes tilt eq's? (would be cool in a pedal format)

Edited by adi77

Share this post


Link to post
Share on other sites
59 minutes ago, Al Krow said:

Time to call in the cavalry!

@bartelby Hey buddy would you mind setting up a patch on your B3 with 3 PEQ effects, two centred at the lowest 20Hz setting and one a notch higher at 25 Hz? All three with Q=4 and maximum cut "-20" and posting what that looks like compared to clean by-pass please?

For extra credit do distortion and signal/noise testing as well...Or_wink.gif

And for better or worse, yeah, I have done this myself way too many times with my DIY stuff.

Share this post


Link to post
Share on other sites
4 minutes ago, adi77 said:

Does anybody still makes tilt eq's? (would be cool in a pedal format)

Thunderfunk amps use them, for one. I've had an onboard/pedal format design set to go for a few years now, but other rabbit holes continue to beckon more seductively.

Share this post


Link to post
Share on other sites
Guest adi77
1 minute ago, Passinwind said:

Thunderfunk amps use them, for one. I've had an onboard/pedal format design set to go for a few years now, but other rabbit holes continue to beckon more seductively.

Cool, thanks passinwind :) 

if you decide to make one please let us know :)

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.



×
×
  • Create New...