Any cab simulator circuit worth building?

[J0K3RX]

Yeah, I only have access to a tablet PC right now so breadboard is not an option for me at the moment. If you look at this link http://schems.com/bmampscom/blackstar/  check out the ds2it schematic. It's a variation of the HT5 schematic without the switching.

[Rob Strand]

ust curious, what happen (in real life) if we ditch 1n5 and 12k in choice switch? and add 1M bias resistor in IC1b?

It's while since I played with that idea.  At 30dB down it's going to be subtle.  There's a few units out there that do this in various ways.  To some degree it is similar to leaking a very small amount of dry signal through (but you get the shelf on the low end as well).  Also, the shelf often results when you try to add a notch.


EDIT: I think JOK3RX 290R should be 390R ?

[Rob Strand]

Yeah, I only have access to a tablet PC right now so breadboard is not an option for me at the moment. If you look at this link http://schems.com/bmampscom/blackstar/  check out the ds2it schematic. It's a variation of the HT5 schematic without the switching.

The thing about cam sims is there different usage scenarious and the "right" EQ depends on where you put them in the chain.

Scenario 1:      Guitar ---> Effect --->  Amp  + Speaker --->  CabSim -> Desk/Record
   The Amp/Speaker interaction adds some bass and treble boost so the Cab Sim only needs
    to emulate the speaker.

Scenario 2:      Guitar ---> Effect --->  Amp  Line/Preamp out  --->  CabSim -> Desk/Record
    The Amp/Speaker interaction is lost so the Cab Sim need to include the bass and treble boost.

    The Marshall SE100 and HK Red Box pro are some of the few that use different EQ for
    lineout and speaker out connection.

Scenario 3:      Guitar ---> Effect ----+--->  Amp  etc
                                                       --->   CabSim -> Desk/Record
    The Amp/Speaker interaction is lost so the Cab Sim need to include the bass and treble boost.
    The EQ of the amplifier is lost, typically being some form of mid-cut.
    The "Cab sim" is now really a cab sim + crude amp EQ sim as it needs to put back the mid-cut.

An example is this one.  The marketing YT videos show effects plugged straight into the unit then recorded.
You can see deeper mid cuts.
http://www.tonebone.com/jdxdirectdrive-specs.php

The Hotline 2 has a cab switch, one setting is flat but there are two other "cabs" which have 400HZ and 800Hz notches. It's difficult to say if these are different cabs or simply covering different usage scenarios.

The ds2it schematic shows some form of mid cut notch before the cab sim.

Scenario 4:      Guitar ---> Distortion Effect with CabSim  or Tube Preamp with CabSim output -> Desk/Record

These cases get pretty blurred as it is difficult to know what part is the effect and what part is the cab sim.
It's not uncommon for the "cab sim" part to have no bass roll-off.  We know that is technically wrong.  The
bass cut-off is usually part of the distortion circuit so the distortions low-cut kinds of covers the speaker's low cut as well.

On top of all that is if you want to add the effect of the mic.

[Rob Strand]

Anyway the main point I wanted to make is the use scenario affects what the "right" eq is.

I've had this idea for some time (like 5 years) but I hadn't  had a chance to gather the data accurately.  It uses the "Wisdom of the Crowds" idea.   I often call it "Wisdom of the Cows" because if you have a lot of "dumb" info the result follows the dumb.  It can't pluck out a single expert opinion which is watered down by general stupidity.

Basically you take a sh#t load of "good" responses, say in dB, then take the average of all of them.  The result is the "centre of good".      The cool thing about using dB is any gain offsets have no effect on the final *shape* of the average response.

You can expand this idea by assigning stronger weights to responses  that are deemed better and lower weights to poorer ones.     If you use weights that are "judge by you" then the average response is the one *you* like.   You kind of remove the "dumb" outcomes. (However, be careful about pulling samples: a unit might have good qualities, say good bass end, but you don't like it overall as it is too bright. There is good and bad.)

Anyway,  so as not to pool too much dissimilar data I tried to isolate some cab sims which had the following common characteristics:
- accepted a line level signal.
- closed box or non-specific.
- have been used by some of the masses with some level of "good" feedback (and obviously bad as well.)
- must have reasonable high-pass and low-pass cut-offs.   No skimped designs or designs which don't roll-off the low-end.

This is no means an exhaustive study.  I wanted to test the idea.    I used to idea using 17 cab sims as data.  The responses are plotted on top of one another.   What is clear is that even though these are considered OK there is an enormous variation.   How can we make sense of it?



Anyway by treating the 17 responses as votes for candidates, I computed the average and median responses.   The result was quite cool.   I've plotted the results below with a few other cab sims so they can be compared:



I suspect the result sounds quite acceptable.  The good thing is the median and average are close.  I've got a circuit which matches the resulting responses but I haven't yet tried to tweak it.

The result should be interpreted as the least offensive to all people.   Keep in mind it was based on relatively good cab sims to start with.      However, also keep in mind if you like a specific tone (bright, dark, bottom heavy) it is unlikely to be correct because you are at an extreme.

Note also the idea of leaking some HF through does not come out in the results because only a few units do that and that info gets watered down.   However it could turn out this is a good idea.   In that case it would be an example where the ideas of a small number of experts gets watered down by the masses.

It's interesting it is not too far off some of the responses of other units, despite the messy starting point data.  Does that mean these designs have sort out the central goodness by trial and error?

The last comment I wanted to make is I didn't use some designs as input data because they had variable controls.  Usually variable controls go to extremes and it is difficult to know where the actual good zone is located, which is much narrower than the range offered.  I would have to build them then narrow it down myself.

[EDIT:  I've added a comparison with the hotline 2 (setting: flatter cab, sand pot mid position 5k, accent on)


Anyway it was just an idea and I wanted to see how it panned out.

[Rob Strand]

Yeah, I only have access to a tablet PC right now so breadboard is not an option for me at the moment. If you look at this link http://schems.com/bmampscom/blackstar/  check out the ds2it schematic. It's a variation of the HT5 schematic without the switching.

I noticed some differences between your HT5 schematic and the factory schematic.
1) At Input, CB switch:   5.1k,     factory 9.1k
2) First low-pass filter:   2x10k,   factory 2x18k
3) Output terminal:        290R,    factory 390R

Are they mods you did or just typos?

[Rob Strand]

FYI.  I had a quick play with the Wisdom of the Cows cab sim.   I transferred filters to DSP because I could do that quicker than building a circuit.   It sounds OK.  I think its sounds close to the JMP1 and the Hotline 2.   The variable highs on the Hotline2 does have something to offer particularly if you use a lot of overdrive.    If you want to do metal chunking you probably want more low end.  The VAL Version 7 2012 has a a lot of bottom end and a variable low-end control.

[ElectricDruid]

Thanks very much for this, Rob. I absolutely love this sort of stuff. It's proper work done with real data! It's brilliant to see so many collected responses compared like that, and interesting to look at the ways they are similar and the ways in which they differ.

One way of making sense of the variation in cab sims is to point out that not all cabs are the same either. Some of these might be looking for a 4x12 sound, or a 2x12, or something more "tweedy", or something more Champ or whatever. So how you sort that out to come up with an overall cab sim I have no idea. But the data does present several interesting ideas for ways a circuit could add some tweakability without getting ridiculous.

They all follow a general pattern of low-end rolloff, a low hump, slightly/not so slightly scooped mids, high hump, and rolled off treble. That's basically a highpass filter with a slightly variable cutoff and a tweak able resonance (amount of low hump) and similarly for the high - a lowpass filter with a tweak able cutoff and resonance. If you used a filter where passband gain decreases with resonance, you'd get more mid scoop as you increased the humpiness. It wouldn't necessarily be any particular cab sim, but it might allow you to get in the same region as quite few.

Fascinating stuff. Thanks again for doing the hard work.

Tom

[Rob Strand]

One way of making sense of the variation in cab sims is to point out that not all cabs are the same either. Some of these might be looking for a 4x12 sound, or a 2x12, or something more "tweedy", or something more Champ or whatever.

Yes it's tricky.   It's one of those things where you can't please everybody.  The compilation tries to contain closed box (ideally 4x12) and non-specific cases.   Even with that restriction the variation is enormous.

An interesting thing I noticed was the Blackstar HT1 has more low-end roll-off than the Blackstar HT5, despite coming from the same company.    The HT1 is a combo with an 8" speaker so you would want the Cab Sim to sound something like the combo speaker.  The HT5 is a head which is why it offers a closed box/open box switch; there is a combo version with a 1x12" .  So obviously the HT1 needs more roll-off. However, maybe the HT1 would sound better connected to a 4x12" cab - so a better sounding cab sim would have more low-end!

So how you sort that out to come up with an overall cab sim I have no idea. But the data does present several interesting ideas for ways a circuit could add some tweakability without getting ridiculous.

I'm convinced you need some form of tweakability.   Some units have a mic position knob  but you have to really question whether that is actually the right thing.  Like if the sim it self doesn't sound like a speaker why have a knob which tweaks a secondary effect?

The cool thing about moving stuff to DSP is I can move the filters around.   For example I can shift the low-pass filter up and down by 5% or 10% and listen to the difference.  On distorted guitar you can hear a difference.   

For the VAL 7 simulator the author gave some samples for unprocessed samples and processed samples.   When I transferred that cabsim to DSP I only approximated the response.  It was still close and I could verify the response of the DSP filter against the spice simulation of the circuit.   When I processed the author's unprocessed samples with the DSP filter they didn't sound *exactly* the same.  I looked at the spectrum and I could see the HF cut-off on the processed samples was about 5% higher.  When I shifted the DSP low-pass filters up 5% the difference was much less.  I'm thinking the 5% could be due to parts variation.  However I also noticed the processed samples had a tad more bass, which was also audible.    The interesting thing is some small differences are audible.

They all follow a general pattern of low-end rolloff, a low hump, slightly/not so slightly scooped mids, high hump, and rolled off treble. That's basically a highpass filter with a slightly variable cutoff and a tweak able resonance (amount of low hump) and similarly for the high - a lowpass filter with a tweak able cutoff and resonance. If you used a filter where passband gain decreases with resonance, you'd get more mid scoop as you increased the humpiness. It wouldn't necessarily be any particular cab sim, but it might allow you to get in the same region as quite few.

Yes most have that pattern. Some leave off the low-cut but it's still somewhere in the signal chain as I mentioned earlier.   To a large degree this pattern is what a loudspeaker does.   The small amount of mid-scoop often comes for free as part of the low and high peaks.  I've noticed some of the bass end tweaks are OK for clean but not so great for metal chunking.  In the past, in DSP, I've created knobs which do various things or do two things at a time and they sometimes sound OK but the always leave you asking for more.     For an analog circuit, the minimalist recipe would be like:
- bass tweak (like VAL 7),
- treble tweak (like the Hotline 2),
- perhaps some mid notches (like the Hotline 2) for different use cases.

You definitely don't want 50 options where only 5 sound good!

As far as covering the most bases how the low end is adjusted makes a big difference.

There still some work to be done on the high-end like is notching (eg. Lart 2 and VAL 7.0) better than just a low-pass?   I know it can be made to sound quite close.   And is leaking some high-end through a good thing?

Fascinating stuff. Thanks again for doing the hard work.

No worries.    I thought I put it up instead of leaving it on my hard disk with the rest of my silly ponderings.

[jhsa]

Has someone built this one??

https://www.diystompboxes.com/smfforum/index.php?topic=70445.0

João

[temol]

Has someone built this one??

https://www.diystompboxes.com/smfforum/index.php?topic=70445.0

João

Yep.. in 1590A and 1590B enclosures. Nice sounding device.

T.

[bobbass4k]

A friend of mine got me to fix his DSM OmniCabSim (V1) so i took the opportunity to trace it out, it's pencil squiggles at the moment but I can put it into kiCad if anyone's interested?

[sergiomr706]

Even pencil sounds good to me. Thank you!

[jhsa]

Has someone built this one??

https://www.diystompboxes.com/smfforum/index.php?topic=70445.0

João

Yep.. in 1590A and 1590B enclosures. Nice sounding device.

T.

Thank you.. I am just about to build one but I am not sure it is really what I want.
When I play live I connect my guitar directly to my SC Ui12 mixer. it has some Digitech am simulators on channels 1 and 2, but I don't really like them. By connecting the guitar directly to the mixer I get loads of fizz when using my overdrive pedal..  A good cab simulator is supposed to cake care of this fizz, right?
Also, I need the cab sim to be always ON no matter what pedal i am using, so no need for true bypass..
No, a real amp is not an option I need to take as few things as I can. Not getting any younger here

João

[temol]

Choosing a cab is a personal preference so it's hard to give any advice. I've built several cabsims and this one is somewhere high on my "I like it" list, mainly because of adjustability of the parameters, but also because of the sound.

ps. Check this forum thread.

T.

[FiveseveN]

SC Ui12

Why not implement the cabsim frequency response in the mixer's channel EQ? You have 4-band parametric EQ + Highpass, which is more than most analog cabsims offer. Or just use the graphic EQ.

[jhsa]

SC Ui12

Why not implement the cabsim frequency response in the mixer's channel EQ? You have 4-band parametric EQ + Highpass, which is more than most analog cabsims offer. Or just use the graphic EQ.

I think this is something to try..
I have been looking at this, perhaps I can emulate with the Ui's parametrics. You forgot the de-esser as well, so, 6 controls.
But with the channel EQ emulating the speaker, I believe I might need some kind of preamp with tone control, right?

Thanks

João

[jhsa]

Choosing a cab is a personal preference so it's hard to give any advice. I've built several cabsims and this one is somewhere high on my "I like it" list, mainly because of adjustability of the parameters, but also because of the sound.

ps. Check this forum thread.

T.

Thank you.

João

[jhsa]

Choosing a cab is a personal preference so it's hard to give any advice. I've built several cabsims and this one is somewhere high on my "I like it" list, mainly because of adjustability of the parameters, but also because of the sound.

ps. Check this forum thread.

T.

Do you have a link for the Bajaman mod to the Simple Cabsim? I can't find it.. 
A friend of mine also listened to your cabsim recordings and liked more the simple cabsim (both flavors)

Thanks

João

[temol]

Link to the mod.

T.

[jhsa]

Thank You..

João