Cytomic "The Scream" stomp box distortion plugin

[pekbro]

The Glue, The Drop, The Scream... in eurorack, would be phenomenally cool.
...Just sayin

I think the best fit for eurorack would be The Glue, being able to run your outputs through The Glue to smooth out levels and make things stick together better I think would be really useful, as long as the cost was low enough (otherwise you may as well just use analog). It would need to be at least 88.2 khz processing, otherwise you'll be losing too much analog goodness.

Digital processing will add latency, and then you break what eurorack is best at, being able to feedback any signal to anywhere else to create resonance paths between various modules, but The Glue will usually be at the end of the chain, so it's not so much of an issue. I love eurorack filters that have an external patch point for their resonance path so you can do this easily, but most cascade filters will allow for this anyway. This is the same thing people do with their mini moogs.

Thanks for that, beyond whether it's in the cards or not, definitely it would be great
to see what you could do with the Eurorack format. No doubt it would be great, with
companies like u-he beginning to test the eurorack waters, hopefully this is an emerging
trend and more great devs like yourself might see fit to follow suit one day.

[abi]

hi there! i just bought the scream and wonder where i can find some presets for it! anyone?

[Arrested Developer]

hi there! i just bought the scream and wonder where i can find some presets for it! anyone?

They will come with the release...

[abi]

hi there! i just bought the scream and wonder where i can find some presets for it! anyone?

They will come with the release...

Ok, thanks for the info!

[andy-cytomic]

hi there! i just bought the scream and wonder where i can find some presets for it! anyone?

You can manually install some presets from this zip file:

https://cytomic.com/files/scream-beta-presets-2.zip

[abi]

hi there! i just bought the scream and wonder where i can find some presets for it! anyone?

You can manually install some presets from this zip file:

https://cytomic.com/files/scream-beta-presets-2.zip

Thank you I got them!

[Oden]

Hi,

I am interested in modelling the Boss SD-1, which there is a preset for. I have a few questions, since I want to get it as close as possible.

The OP amp:
- JRC4558 has a slew rate of 1.7 V/uS according to the fact sheet, but the plugin has a default of 1.0? The SD-1 uses JRC4558DD, which presumably is a low noise variant. I don't know what this means in practice, but the model can be assumed fine?

The diodes:
- The diodes for the newest iteration of SD-1 are 1N4148, but older ones had 1N914, 1S2473, 1S1588. The last two are not emulated in the plugin. For the question, what is the meaning of post-fix A/B on 1N4148 (for sure not 1N914 A/B)? The post-fix B and standard 1N4148 match the 1N4148 pedal best.

The schematic/parameter values:
- I believe there is a small typo in the preset, the value of R118 should be 1 meg. This seemed irrelevant to the sound. What is the extra resistor RQ104 (and RQ102) and why can they not be edited? Level pot 92.8 instead of 100k?

General:
Is it possible to provide some documentation on what the meaning of the different parameter values relating to the diodes and OP amp? Is there a way to bypass values other than typing large/small values?

Overall the plugin is very close to the box. The slight difference is that the pedal does not clip quite as hard as the plugin. The harmonics taper slightly faster and the odd harmonics are less pronounced on the pedal. Slightly brighter/more fizzy feel on the plugin.

[andy-cytomic]

Thanks for the great questions! It sounds like you're wanting to get more serious about things, but please be warned it is a deep area. The short answer to this is: circuits are complicated, and components are not exact, and use your ears for what you like the sound of!

I'll answer your specific questions inline below:

Hi,

I am interested in modelling the Boss SD-1, which there is a preset for. I have a few questions, since I want to get it as close as possible.

For the default preset I matched my particular TS-808 very closely by doing a lot of measurements, and this took a lot of time. I added extra components to the circuit so it could be "bent" into other types of tube screamer, including an SD-1. I am guessing you want to be able to get The Scream to match as closely as possible to your particular SD-1. That will require doing a lot of measurements and taking a lot of time fiddling the component values till they match. I cannot help much with that since I don't have your particular SD-1, so can't tell what the values should be.

The most systematic and full proof approach would be to de-solder all the components, measure them all in detail, then solder the pedal back together. You could then just enter all the parameters of all the components directly and you would have an excellent match. This would require a considerable amount of test equipment and expertise to measure things like the slew rate of op-amps, and the saturation characteristics of diodes etc.

So why is this so complicated? Perhaps a little background on circuit components is required for some perspective:

A datasheet is guide only. It doesn't state the exact characteristics of any particular component, it just specifies something "close enough" to what the component will actually do and give limits on when it will blow up and when it should work as expected given certain bounds of voltage, temperature and current/power. To make sure it will actually do what the datasheet says in your particular application you really need to build the circuit and test it out.

Most components have terrible tolerances, 10% is average for resistors, potentiometers and capacitors are usually worse. To add complications there are multiple types of resistors and capacitors and each one has different properties that a circuit designer needs to know which is best bang for buck for a particular application.

Ok, so now back to trying to model this mess with an expectation that all the nice and neat numbers of a bit of paper called a schematic / datasheet are only a rough guide to the underlying reality of the physical circuit.

The OP amp:
- JRC4558 has a slew rate of 1.7 V/uS according to the fact sheet, but the plugin has a default of 1.0? The SD-1 uses JRC4558DD, which presumably is a low noise variant. I don't know what this means in practice, but the model can be assumed fine?

Anything from 1V/uS to 5V/uS will sound pretty much the same in this circuit, and most non-vintage chips will be more like 5V/uS as per their updated datasheets.

The diodes:
- The diodes for the newest iteration of SD-1 are 1N4148, but older ones had 1N914, 1S2473, 1S1588. The last two are not emulated in the plugin. For the question, what is the meaning of post-fix A/B on 1N4148 (for sure not 1N914 A/B)? The post-fix B and standard 1N4148 match the 1N4148 pedal best.

I made two different virtual "batches" of 1N4148, batch A and batch B which have slightly different values but within the tolerance of what a 1N4148 is. Use whichever you like the sound of best. If you want other diodes grab some spice models from the internet and enter them in and see if you like them. Please be aware that most spice models are also only rough guides, they are not an exact model of your particular didoes. If you want to match your particular diodes in your SD-1 then I suggest desoldering them and setting up a test to characterise each one individually.

The schematic/parameter values:
- I believe there is a small typo in the preset, the value of R118 should be 1 meg. This seemed irrelevant to the sound. What is the extra resistor RQ104 (and RQ102) and why can they not be edited? Level pot 92.8 instead of 100k?

I measured the level pot in my TS-808 and it was 92.8k (to the nearest 0.1 of an ohm). This is within 10% tolerance of 100k. A pot also doesn't usually go all the way to 0 ohm, which is why there is a minimum value you can also include.

RQ104 and RQ102 are resistors that are in place of switching JFETs to lower the cpu load. When the JFET is switched it doesn't make much difference to the tone, but I wanted to model the little chirp you get when actually switching, which the resistors do well enough when their values are ramped up / down to give a basic emulation of what the JFETs are doing. The "rjfet_on" and "rjfet_off" values can be edited, but which value each resistor has depends on the position of the flip flop "active" button, they swap between the on value and the off value. For the generic SD-1 make rjeft_on = 22k and rjfet_off = 10meg, and yes, R118 should be 1meg, thanks for spotting that!

General:
Is it possible to provide some documentation on what the meaning of the different parameter values relating to the diodes and OP amp? Is there a way to bypass values other than typing large/small values?

There is a lot of information on the internet about op-amp and diodes parameters, or you could do an electronic engineering course to learn more. The entire area is highly technical, and it is beyond the scope of the plugin to explain things much detail, and most people will just glaze over and be put off by too much information. Here are a couple of links for you to read:

Boyle op-amp macro models-
http://www.ecircuitcenter.com/OpModels/OpampModels.htm

Dode models parameters-
https://www.allaboutcircuits.com/textbo ... ce-models/

There is no way to bypass a component that is in the model, the model always models everything in the circuit. For example, where you type in "0" for a resistor value you actually get 0.0001. For resistors and capacitors I could support typing in "open" or "short" to indicate an open or short circuit, but I think just typing in 0 or 100meg is fine, and you know what you are getting.

Circuit solving is a bit complicated when it comes to bypassing a component it is actually the same as modelling a new circuit. So to actually fully bypass a component I would need to solve 2^n different circuit models where n is the number of things you want to bypass, so for this "simple" circuit of a tube screamer with around 50 components that would be around 2^50 = 1e15 different circuit models to develop and test, obviously not going to happen. Even if I could develop each model in 1 second that would still take 300k centuries to finish and if each model took 1k of compiled machine code it would take around 1000 Peta Bytes of storage to actually store.

Overall the plugin is very close to the box. The slight difference is that the pedal does not clip quite as hard as the plugin. The harmonics taper slightly faster and the odd harmonics are less pronounced on the pedal. Slightly brighter/more fizzy feel on the plugin.

So by now you should expect this one: by "the box" do you mean "your particular box"? I am guessing yes. Your particular box max have better capacitors than my TS-808, so I would go there first, and lower all ESR of all the capacitors down to 1 ohm. Also try making R107 or C105 bigger, as this will make the sound duller. Also check which input and output BJTs your SD-1 has and enter different values for those. Another thing to take into account is which type of soundcard you are using, you will need to match the oversampling filters and input and output impedance of your soundcard for an accurate comparison.

Ok, that was probably a bit much to take in, so sorry for that, but I hope I have been able to adjust your expectations a little as to the situation and how many variables there are and how in-exact things are Another thing you may want to do is grab another SD-1 from a different time (10 years difference would be fine) and listen to the differences between it and your SD-1, this may give you some more confidence that these differences are real and totally valid and it really comes down to which tone you prefer, not which is "correct", since obviously they are both actual SD-1 boxes

[jens]

Ok, that was probably a bit much to take in, so sorry for that

He asked for it.


And what a great reply!

[Oden]

Thanks so much Andy, fantastic reply. I love detail, not too much at all, apparently other KVRers loved it as well.

I will post some pics and demos once I get it done (may be some time).

[SamDi]

Wow, what a deep digging answer. I am impressed, how deep it can go. My ears just can‘t resolve this small changes in sound, related to small changes in the components, but maybe this is, because I am just using it for synths and not guitars. Maybe subtle changes can be heard better there. BTW, what is the current release date? Sorry if I should have overread this, some posts before.

[Havok]

Finally got.round to getting this, had a play around with it last night. Was sat tweaking the "mods" section for about 5 minutes wondering why I couldn't hear any difference before I noticed the mods switch haha

Sounds f**king incredible, great work Andy!

[acousticglue]

I did same,thing at first lol

[andy-cytomic]

Thanks so much Andy, fantastic reply. I love detail, not too much at all, apparently other KVRers loved it as well.

I will post some pics and demos once I get it done (may be some time).

Good to hear it helped

[andy-cytomic]

Wow, what a deep digging answer. I am impressed, how deep it can go. My ears just can‘t resolve this small changes in sound, related to small changes in the components, but maybe this is, because I am just using it for synths and not guitars. Maybe subtle changes can be heard better there. BTW, what is the current release date? Sorry if I should have overread this, some posts before.

It's pretty much just when you hard switch between two things that most of the time you will notice some differences. In isolation if you just listened to any old TS-808 on a guitar or synth you would just shrug and go yeah, that's a Tube Screamer.

I've spent a while getting all the updated security stuff and installers all sorted out, The Drop is released with it and it has fixed all security issues thus far, which is great - I've gut a whole bunch more checks in there to verify that the authorisation files can be written and try and change permissions on folders if they are wrong. I'm rolling out a new build of The Glue right now with all this new stuff, and then it's back to The Scream. Still don't have a hard date, but it's within a month or two now till I'll have a new beta to share.