Can tube sound be replicated via plugins?

Discussion in 'Sound Science' started by roughsleeper, Mar 30, 2013.
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  1. RoughSleeper
    Many say tube sound is nothing more than EQ and designer coloration, if this is the case would it be possible to exactly replicate tube sound through the use of a plugin?
  2. p a t r i c k
    I guess by plug-in you mean some thing for a replay program such as iTunes.
    I often think that people pursuing a valve sound ("tube sound" in US) might do better buying a valve buffer rather than a valve amplifier. The reason I say this is that you can just unplug the valve buffer and return to the non valve sound, which I think will be a bit of a relief when you get fed up with it.
    Here is a valve buffer, or tube buffer:

    It is a "plug-in" but maybe not the kind you were discussing :)
  3. RoughSleeper
    I should have clarified, by plugin I mean a computer plugin. This is assuming a person is using their computer as their source and the plugin is being run at the same time through the program thats playing the music or as core audio.
  4. mikeaj
    Different tube devices affect the signal in different ways, particularly if you're talking about amps—then the load used would be a factor as well.  Some circuits with tubes in them don't really change the sound in any significant way.  How are you defining a tube sound?  What are its characteristics?
    There exist a lot of effects processors, even amps with a tube-sound kind of mode, software, plugins, etc. that try to emulate a tube sound, but it may or may not be really like any particular example you might think of.
    Something like the Carver challenge shows that you can build hardware to emulate a tube amp (one that changes the sound a lot, in a characteristic way) sound very well, around to the point where seasoned reviewers can't tell them apart.  So doing the same in software wouldn't be difficult.  The issue would be that you'd need different code or different parameters at least, if the load changes, maybe if output level changes, apparently even if the tube amp is using a power conditioner or not because its power supply is that flaky and temperamental, etc.  Again, it really depends on what you're meaning to emulate.
  5. jaddie
    It's possible to exactly emulate any device, it's mostly a question of taking the right measurements of the device you're trying for. It's what Carver called the "transfer function".  Like mikeaj said, the "device" may be a combination of an amp and a load.  I'd envision a tube emulator to have controls that select from a few specific famous amps, and a few specific famous loads.  Then tweaks for the amount of feedback, quality of the output transformer, etc.  Heck, while we're at it, throw in characteristics of a few tube-era speakers.
    Just so long as we realize that in truth, a tube device with a clearly "tube" sound is distorting the audio in some way, not improving the accuracy of reproduction.  Also, a plug-in may emulate tube sound exactly, but it won't emulate the tube amp experience.  A large part of why people like tube electronics is the awareness of the tubes in ways both visual and tactile.  Ever see a tube amp without visible tubes, usually right out where you can't miss 'em?  That's part of the fun, and something a plug-in can't do.
    I question the motives behind plug-ins that emulate, for example, analog tape recorders, replete with high THD, IMD flutter, scrape flutter, and wandering azimuth.  Or plug-ins that emulate vinyl, with surface noise and mistracking distortion.  Why on earth? Just because we can?
    I think I'll get a vinyl emulator that adds noise, pops and ticks, and follow it with a vinyl de-clicker and cleaner and just let the plug-ins duke it out with each other. 
  6. ultrabike
    I think linear distortion might be straight forward to emulate. Non-linear is possible, but perhaps a bit more involved.
  7. jaddie
    Yup, equalizers are everywhere.
    A bit, but not really challenging.  Googling "tube emulation plug-in" returns quite a few references to products and free plugs.  None of this stuff is hard to do, the hardest part is deciding what to do.
  8. kramer5150
    Many say tube sound is nothing more than EQ
    No this is incorrect... at least in the sense of a PURE-EQ that does nothing more than boost/cut frequencies.  Tubes also add distortion and other harmonic "artifacts".
    if this is the case would it be possible to exactly replicate tube sound through the use of a plugin?
    You'd think it would be, as common as tube preamp and amp simulators are in the recording industry.
  9. jaddie
    While this is true, the distortion is not something that adds to the "tube sound" in a positive way, and as it turns out, people who have successfully simulated the tube sound (i.e. Carver) did not add distortion, they just did it with a response modification (a type of EQ). 
    Tube simulators can, and some do add distortion.  
    Beyond the non-linear mechanisms that create harmonic distortion and intermodulation distortion, there are no other mysterious "harmonic artifacts".  
  10. ultrabike
    Perhaps the main ingredient of "tube sound" perception is frequency response coloration...
  11. wuwhere Contributor
    Here are three frequency response curves from three different amplifiers, two all tubes and one solid state.
    Audio Research Classic 60, all tube:
    Conrad Johnson Premiere Eleven, all tube:
    Krell KSA-50S, solid state:
    Fig.1 Krell KSA-50S, frequency response at 1W into 8 ohms, in balanced mode (top), 2W into 4 ohms (bottom), and into dummy load (top at 2kHz) (right channel dashed, 0.5dB/vertical div.).
    If you are shown these graphs without knowing which is which, can you tell the tube amp from the solid state?
  12. jaddie

    I might if they were plots of the amps all driven into the same reactive load. And 8 ohm resistor won't show you much.
  13. wuwhere Contributor
    An 8 ohm resistor is not a real world load, I agree. But 'might' is not good enough with real world loads. I have 3 all tube speaker amps and 1 mosfet hp amp that I listened to through my HE-6 hp. If I listen to each with the same music track I could probably tell with a high certainty which is which only because I'm familiar with them. If not there is no way to tell.
  14. jaddie
    You've just verified that it's possible to build tube amps without the "tube" sound.  It's also possible to build in more or less "tube" sound, at the designer's whim.  That's why I said I "might" be able to tell with reactive loads, because that's where you'll see response differences.  But I also might not, it depends.  I've personally done high resolution response plots of many different devices, and when I got to a vintage Marantz tube amp I was surprised and impressed with how non-flat the response was into a reactive load similar to a speaker with high-order three-way crossover vs a non-reactive 8 ohm load.  It was the only reason I could find that tube amps would have any sort of audible signature, assuming distortion is at a reasonable level.
  15. ultrabike
    Audio Research Classic 60
    Going by Stereophile, the Audio Research Classic 60 is not all tube, it's a "hybrid tube/FET power amplifier." Furthermore, I found in the article something of interest:
    "Unlike a good solid-state amplifier, which approximately acts as a voltage source, meaning that its output power will almost double as the load impedance halves, the Classic 60 is a typical tube design in being more like a current source: halve the load and the output voltage falls to maintain the same maximum current. The effect of this character on sound quality is not known, though it does imply both that such an amplifier will run out of steam with real-world loudspeakers somewhat earlier than a good solid-state design, and that it will retain less effective control on the loudspeaker near the clipping point."
    A current source and a voltage source will not behave the same way when driving a reactive load. This might partially explain the typical tube and solid state amp sound characteristics.
    Conrad-Johnson Premiere Eleven
    This one does seem to be all tube. From the same article at Stereophile:
    "Second, it has been postulated that all audible differences between well-designed amplifiers are due to the differences in frequency responses caused by the voltage-divider action between the loudspeaker impedance and the amplifier's source impedance. The latter measured between 0.48 and 0.56 ohms for the C-J, varying only slightly with frequency; and 0.28 ohms for the Krell KSA-50S, giving rise to response variations when loaded by the B&W Silver Signature (fig.3). The top trace is the Krell; the bottom, offset by 1dB for clarity, is the Connie-J. It varies by about twice as much as the Krell, reaching ±0.25dB. The tube amp's more depressed top two octaves were audible as a very slight lack of air, yet it was the C-J's lower mids that sounded warmer—the opposite of what these curves would suggest."
    "Fig.3 Krell KSA-50S (top) and Conrad-Johnson Premier Eleven A (bottom), frequency response at 0.5W into B&W Silver Signature loudspeaker (0.5dB/vertical div.).Fig.3 Krell KSA-50S (top) and Conrad-Johnson Premier Eleven A (bottom), frequency response at 0.5W into B&W Silver Signature loudspeaker (0.5dB/vertical div.)."
    Tube amps might typically have higher output impedance, which might account for some sound perception variations.
    Krell KSA-50S
    "The KSA-50S's input impedance measured 49k ohms unbalanced, the same for each leg of the balanced input; its output impedance was highish for a solid-state design at a calculated 0.28 ohms."
    This is probably high considering it is supposed to drive ~8 and ~4 ohm loads.
    "The slight (+0.08dB, -0.16dB) variation is due to the interaction between the '50S's output impedance and the load..."
    That is, the Krell might be a high impedance amp relative to other typical SS designs.
    I agree that one can have a wild frequency response solid state amp, and crazy frequency response tube amp. Note however that high output impedance, and voltage vs. current source behavior might account for the typical sound perception differences.
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