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Modeling / Analog / Digital / Solid-State Community Posting

Discussion in 'Modeling Amps, Plugins and Apps' started by jaytee32, Aug 10, 2015.

  1. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    Hi *,

    A while back we had a thread going (that I started) about the differences between the terms "solid state", "analog", "emulator", "modeler", "profiler" etc. There was also a followup round. My intent was to have this be some sort of recurring post for newer people to the group, as these discussions keep coming back to life. I may have started the discussion, but the post below is the summary of discussions involving a number of TDPRI people, please refer to the original threads to see the cast of characters contributing:

    http://www.tdpri.com/forum/modeling...1482-modeling-analog-digital-solid-state.html and
    http://www.tdpri.com/forum/modeling...-emulating-digital-solid-state-draft-2-a.html

    If you have a strong disagreement with the post, might be good to browse through those original discussions as a lot of the disagreements boil down to differing points of view on ill-defined terms like "modelling".

    Here goes, hope this is helpful especially to newcomers!
    -------------------------------------------------------------

    There's a lot of confusion surrounding the terms listed in the subject. For example we see posts confusing "solid state" with "digital" and "emulation" with "modeling". This post tries to clarify that confusion for the benefit of anyone reading.

    First let's talk about the terms that are well defined.

    1) solid state: this is a pretty old fashioned term actually, all it means for the purposes of amplifier discussions is : no tubes. Technically it means that all the electronic components are constructed out of solid materials. Vacuum tubes are of course not solid -- that's the distinction. Solid state doesn't mean anything else except "no tubes". "Transistor" amps are solid state amps (as long as they don't contain some tubes too, in which case they are called "hybrids").

    2) analog/analogue and digital : analog circuits work on an incoming signal as a continuous value, and the various pieces of the circuit work in the same way. Digital circuits work basically on numbers, doing operations on those numbers. For a guitar amplifier, the input signal is converted to a sequence of numbers, then inside the amp calculations are performed on those numbers resulting in an output signal.

    Think of analog like a measuring cup: you pour water into it, however much or little you like; depending on how much you pour in, the water level in the cup rises or falls. Digital is like your bank balance : you can only put money in in units of cents. So your bank balance is always a whole number of cents.

    Usually when people speak of digital electronics, they mean something that works as a computer, because modern computers also work with digital, discrete values ... data are stored in memory locations that can hold whole numbers of various sizes, just like the cents in your bank balance.

    Analog vs digital is not strictly related to solid-state/transistor/tube. One relation which (as far as we know always holds is tube amps are always analog. But not the other way around ... analog amps are sometimes tube, sometimes solid state.

    In theory you could build a digital tube amp, but we don't know of any ... so another relation is digital always means solid state. Again, not the other way around: solid-state (transistor) amps are sometimes digital (like a Peavey Vypyr) and sometimes analog (like my old Randall Commander II). There are also some hybrids, like the Vox Valvetronix that has a tube (analog) preamp section and a solid-state (digital) modeling and section.

    Now there are some terms commonly used (say "marketing hype three times real fast") which are not so well defined. This is what a bunch of us on this forum came up with for definitions to assist us in our discussions, and people new to modeling amps to help understand some of the terms being thrown around.

    Here are some common terms:
    • a clone or copy is an amp that tries to copy another amp, and that's about it. think of all the '57 deluxe clones out there.
    • an emulator is an amp that (analog or digital, usually digital) tries to recreate sounds by making a "virtual circuit" that is identical to some other amp's circuits. Examples are the Blackstar ID (which emulates different power tubes as well as how a tube would interact with the speaker) and the Fender Cyber Twin.
    • a profiler is an amp that can capture the sounds made by another amp and reproduce them

    Finally we call a modeler any amp that can be configured to "sound like" other amps, or that allows you to construct a very wide range of specific tones, by choosing different combinations of settings. Given this definition of modeling, it could be achieved using many different techniques, for example:
    • using an emulator principle to simulate various amps, effects, etc as described above
    • using digital (DSP) techniques to transform an input signal into the same output signal an amp or effect would have produced. Technically speaking, this would be emulating the end-to-end signal transfer function, rather than the electronic circuit itself.
    • using a profiling technique to copy how another amp responds to the guitar
    • having an extremely flexible tone stack, power stage, or switchable internal circuitry that allows a wide range of amp sounds to be created.

    Note this last point is a ill-defined grey area, as it's not well-defined just how flexible your tone stack needs to be for you to call it "modeler". Two examples are the Tech Trademark series and the Egnater Tweaker. The Tech21 web site refers to the SansAmp (which is at the heart of the Trademark) as "analog amp modeling". The Tweaker is not usually referred to, nor marketed, as a modeling amp. However the switches are named "vintage/modern", "usa/ac/brit", similar to the Trademark's "calif/british/tweed" and "us/uk/flat" and even to the Roland Cube's switch between "Black Panel", "Brit Combo" and "Tweed". The intent in all cases is to recreate, or at closely resemble, sounds specific to other amps.

    So a modeler could be anything from an extremely flexible analog solid-state amp, or tube amp like the Tweaker, to a DSP-based amp like the Peavey Vypyr or Fender Mustang, to a profiler -- the main point of modeling is not "how you do it" but "what are you trying to do" -- and that is to sound like multiple other amps.

    Emulator, DSP, very flexible tone stacks, profiling -- this all refers to the "how you do it" part.

    Hope this post helps further understanding and useful discussion in this forum!
     
    GrantR likes this.

  2. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    Came across a discussion about whether the Katana is, or is not, a modeling amp ... decided it was time to bump up this post :)
     
    Staypuft1652 likes this.

  3. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    And again, discussions about whether the Katana is, or is not, a modelling amp ... bump time :)
     

  4. Allthesound

    Allthesound Tele-Afflicted

    Oct 21, 2011
    Connecticut
    So many inaccuracy's in your post tells me you have no real understanding about the underlying principles of what is commonly accepted as present day modeling. I see it as a disservice to new comers.
     
    beagle, SustainerPlayer and codamedia like this.

  5. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    Perhaps you'd care to point out what the inaccuracies in the post are? I contest your statement about me having no understanding about the principles behind how modelling amplifiers work, but again, if you care to be specific, I am listening. It's a community post after all, if you have better ideas, they will go in the post.
     

  6. BigDaddyLH

    BigDaddyLH Telefied Ad Free Member

    Class D amplifiers are not necessarily digital, right?
     

  7. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    It's a good question ... I actually had never heard of a class D amplifier, never made it past A and AB. Looking at what wikipedia says, I would have said "almost" - like digital, the amplitude coming out of the transistors is either on or off, but the pulse width, timing, and separation are not fixed as they would be in a digital system. Then I came across this quote in the article:

    The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits or include digital signal processing devices, the power stage deals with voltage and current as a function of non-quantized time. ​

    That non-quantized is another way of saying that the timing, width, and separations are not fixed. I guess to the extent we trust wikipedia and my gut feeling (and yours too I guess), the answer would seem to be "no".
     

  8. Digital Larry

    Digital Larry Tele-Holic

    517
    May 30, 2017
    Silicon Valley, CA
    I wouldn't describe a class D amplifier as "digital" - but some people probably do. My understanding is that they use pulse width modulation in the output stage, which reduces power dissipation in the output transistors quite a bit - they are either "off" or "on". That switching takes place above audio frequencies and is filtered out by a low pass filter prior to going to the speakers. Maybe in some pedantic way it could be considered digital, but AFAIK it is not doing calculations of any sort.
     
    jaytee32 likes this.

  9. luckett

    luckett Friend of Leo's

    Jun 14, 2011
    .
    Class D is digital in the sense that it uses PWM to control the binary state of the power transistors. PWM is inherently digital due to it's discrete binary mode of operation.
     

  10. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    PWN = pulse width modulation. The information is encoded in the width of the pulses and their separation. If you look at for example the circuit diagram here:

    https://www.maximintegrated.com/en/app-notes/index.mvp/id/3977

    there's nothing digital about it ... the output is "on" (binary one) when the input signal exceeds the internal oscillator's triangle wave, and zero otherwise ... all the information is in the width of the pulses and their separation, not in a numerical value represented by the ones and zeros as in a binary/digital computer.

    Again, I see the definite similarities, but if we agree to call it "digital" it's not the same digital as in a digital computer. Just as an independent data point, the article cited above does not mention "digital" anywhere.

    Edit: this is a nice article explaining why "digital" is a misnomer, how some class D amps do have a digital stage control stage, and (in their opinion) why the pure-analog class D amps are better than the ones with the digital control stage. Nice article.

    http://www.audioholics.com/audio-amplifier/the-truth-about-digital-class-d-amplifiers
     

  11. luckett

    luckett Friend of Leo's

    Jun 14, 2011
    .
    You just described it as being a binary signal. Binary signals with discrete on/off states are digital. You don't have to have numerical values represented for a signal to be digital. The PWM signal used in a Class D amp is digital.
     
    beagle likes this.

  12. Cesspit

    Cesspit Tele-Meister

    391
    Oct 16, 2014
    Oxfordshire England
    To deep for boys. My little brain can't keep.
    I thought there were two types of amp, those with valves and those without. Makes sense that way.
     

  13. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    I agree that I described it as binary - it's either off or on. Digital is (as far as I know) always binary, but not necessarily the other way around. A light switch on the wall is also binary (on or off) but it's not digital.

    I just took a look at the Webster definition of digital, and I'd still say PWM isn't digital, but I think the definition is vague enough that one could make an argument either way. Are we both right or both wrong? BTW there is one of the definitions in Webster that I really disagree with :

    • electronic
      • digital devices/technology
      • also : characterized by electronic and especially computerized technology
      • the digital age
    Basically saying anything electronic is digital, which means my Pro Reverb is digital ;-)
     

  14. codamedia

    codamedia Friend of Leo's

    Apr 4, 2009
    Western Canada
    :confused: o_O... Can you please explain to me what those 6L6 tubes (2 or 4 depending on model) are doing in the larger Peavey Vypyr's since you say those are solid state (transistor) amps and that you don't know of any digital tube amps?

    IMO: In your effort to educate people you are confusing amp sections and branding many things inaccurately which does nothing but muddy the waters even further.
     
    beagle and Allthesound like this.

  15. luckett

    luckett Friend of Leo's

    Jun 14, 2011
    .
    A binary signal is the most basic and fundamental of digital signals. Finding a internet dictionary of colloquial English that doesn't state that doesn't mean it's not so. Last time I checked, Webster's is not the definitive source for technical info. Trying to using it as a primary source for a technical definition is a bit suspect. I suggest you go ask someone who has domain expertise on the subject to educate you.
     
    beagle likes this.

  16. burntfrijoles

    burntfrijoles Poster Extraordinaire

    To me the Katana is not a modeling amp. It has 5 basic tones for clean, crunch, lead, "brown" and acoustic. There is nothing that I have seen that suggests they assiduously tried to recreate the specific characteristics of individual amplifiers. It seems to mostly be a plug and play type amplifier. It's almost like a digital version of an Egnater tweaker or (stretching it) a Mesa with the clean, blues and lead sections.
    Modeling amps on the other hand purport themselves to emulate specific amp brands down to differentiating models. The options are in the user interface. It could certainly be argued that they only do their jobs to varying levels of accuracy.
    Regardless it's mostly marketing semantics.
     

  17. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    Hi, I do have the domain expertise, and I did ask some of my colleagues today (these are guys who build next generation computers that are not yet available to the general public yet). Funny how people assume that I don't have any qualifications. I used the dictionary as a compromise; I am a physicist and am aware that we use terms (like "force" or "theory") that have specific definitions for us, but mean something totally different in everyday English. I am making the assumption that most people reading this are not scientists or engineers.

    Anyway, these colleagues of mine agreed with you on PWM being a digital technology! In the discussion that followed, we understood the reason: my definition of digital is old fashioned.

    I am old enough to remember when the digital revolution started, when it referred specifically to a sequence of bits. The generally accepted definition within the younger crowd is anything that works on a binary sequence. They even went as far as to say that a light switch is digital, because it's either on or off. Thanks for educating me!
     
    Last edited: Feb 8, 2018

  18. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    Agreed that it's mostly marketing semantics, and agreed that in some sense, a Katana is a digital brother of an Egnater Tweaker. On the other hand, in our "best we could do" terminology (trying to escape the hype), both the Katana and Tweaker are made to sound like several different types of amplifier, and in that sense we called it a modeler. Given the hype, there is no strict definition of modeler, so I can't really disagree with you. Hope you can see what we were trying to accomplish with the post!
     

  19. jaytee32

    jaytee32 Tele-Meister

    406
    May 30, 2011
    Netherlands
    Hi, I did not realize that earlier versions of the Peavey Vypyr were Hybrid models that included tubes. When we wrote the post a couple of years ago, these models were out of production. I just checked right now and they are no longer listed on Peavey's site, all the Vypyrs being produced are full solid state models without tubes. You are exactly right though, the older models are not pure solid state if they have tubes!

    You misunderstood what I meant by digital tube amps. I don't mean that there are no digital amps that also have tubes; there are a lot of those, like the older vypyr models. What I mean is that all the digital parts of those amps are solid state. It is possible to build a fully tube based digital amplifier, so no transistors included. The very first digital computers were also tube based .. the ENIAC had 20,000 vacuum tubes.

    The point I was trying to make is that "analog vs digital" is something completely different than "solid state vs tube". Not everybody understands this. I saw just yesterday a post on the Amp Central forum where somebody said "doesn't solid state mean digital?" We illustrated in the post that in principle you could have
    • a solid state digital amp
    • a solid state analog amp
    • a tube analog amp
    • a fully tube digital amp
    and then I said that as far as I know, nobody has ever built that last one. I bet if you built a fully tube based digital amp, it would be as big as a small high school!

    Do you still think it's inaccurate? Also, how could I rewrite that section that would be clearer? I am open to suggestions.
     
    codamedia likes this.

  20. burntfrijoles

    burntfrijoles Poster Extraordinaire

    Not really but I'm a little slow.
    It really doesn't matter the technology or the platform, the only thing that matter is outcome which, in this case, is tone or tones.
    I'll just leave it at that and butt out of this thread.
     
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