renshen1957 wrote:Cliff Schecht wrote:
Sorry but I have to strongly disagree that digital signal processing can't accurately reproduce the subtleties of a tube amp. Anyone who is well versed in modern technologies and capabilities would realize how benign that sort statement has really become.
One of my good friends and I have spent hundreds of hours discussing and designing digital systems that can accurately emulate analog without sounding like, well, emulations. We call it "analog inspired digital" style design and while I honestly can't program for shit, I've spend a lot of time figuring out and studying quirks in analog and my buddy will figure out how to model whatever phenomenon in digital. While our focus is on analog synths at the moment, I can promise you that we could (and eventually will) shift our focus to modeling the strange things that happen when you push a tube amplifier into the non-linear operating regions.
The thing is that a lot of the digital stuff that has been introduced so far has been complete crap and this has tainted a lot of peoples views of what digital modeling is really capable of. It's a shame too because as hard as some try to change peoples opinions, guitar players are some stubborn bastards and it's hard to undo the damage that has been done in the past. All I can really say is give it another 10 years and I bet many people will change their tune (tube?) when it comes to digital modeling stuff.
Hi,
Although not as clearly written as I would like to have (I posted past midnight my time after a long day's work and sleep deprivation from the night before), I think I will stand pat on my statement that Digital Simulations to date have promised much and delivered less than the hype.  
I agree that with another decade there will be advances in digital modeling.  
Whether these advances will be up to the task to change tube amp adherents is another matter. After all if it isn't broken, why fix it? When one's tone signature is perceived as what makes one unique or what is keeping you employed and paying the mortgage, I can understand the tenacity of Guitar players and tube amps.
You wrote, "I have to strongly disagree that digital signal processing can't accurately reproduce the subtleties of a tube amp."
Well, the track record for digital signal processing hasn't been that successful to date. At best it would be a D- for tube amps.  Maybe C for digital instruments as I will comment below.
You wrote, "While our focus is on analog synths at the moment."
As someone who worked with (an occasional on) analog synthesizers in the 1970 (Moog IIIP, Mini Moog, Buchla etc), these devices were all Solid State.  (No company to my mind produced a classic analog tube synthesizer for retail sale used by bands that I am aware off.)
I have admiration for your accomplishments, emulating a solid state device with another solid state isn't exactly the same thing as emulating either tubes or for that matter acoustic instruments.
The general impression in related area of digital reproduction and/or the use of digital sampling is that no one to date has built a digital piano that among blind listening tests (to eliminate the psycho-acoustic factor) couldn't be distinguished from the real thing amongst pianists.  I could say they same about sampled sounds (software for digital organs for $100,000 installations in Churches), and Harpsichord samples off 18th Century instruments. I've played Pipe Organs and digital organs) and as audience member (organists are diehard friends and will fill the chairs at each others performances) as well as the latest digital harpsichords software and real harpsichords, and my conclusion is that pipe organ builders and harpsichord makers aren't going to go extinct in the near future (unless the economy keeps being depressed) or in the next decade for that matter. 
(I would extend the above observations to the best software for orchestral instruments. At least I can tell when a score has real instruments or canned ones.)
As to the quality of the sound (tone replication) among the players of digital pianos and organs, the consensus is these instruments are used for their expediency and convenience not because tonal signatures had been cloned to a tee.  Ask any major keyboard player and they will say it beats trying to transport or rent have delivered a grand piano, a synth, and an organ to a gig. The equivalent of a Line 6 amp for cover bands. 
Ask if it is indistinguishable from the real thing, and the replies are essentially a firm negative.  For example, when I last talked to Goldy McJohn (yes, the Goldy McJohn) about his keyboard he was playing (it produced a good replica of a Hammond B-3 in instrument about the size of a computer keyboard), he replied that it got the job done was good because he couldn't get the roadies to deal with transporting and lifting a real Hammond (tube model).  He said he would gladly switch back to the real deal in a heartbeat (he wasn't 100% convinced of the digital replication) if could find a practical solution to transportation.  To his credit, he made the keyboard sound very close to the original.
Electro Harmonic's Holy Grail emulation of the classic tube Spring reverb by Fender is advertised as "so faithful that even Dick Dale couldn't tell the difference."  (The Grail is nice, for sure. But after 40 years of loud rock music and chemotherapy for cancer, I'm not sure Dick Dale's hearing was in such great shape when the Grail came out.) 
At least among the guitarist I know (my son included) digital delays of any type are used as a separate effect on its own for its flexibility. Many eschew using the "analog" settings and use the real deal as a separate effect and especially on recordings. And those Tel Ray Oil Can delays have their proponents, too, although I do not know of any digital simulations. 
Ask a Concert Classical Pianist about digital and they will flat out say digital does not "cut it" on terms of performance being exactly equal and dynamic as an acoustic piano.  Even with the instruments with hammer touch keyboards, the tone wasn't indistinguishable from the real thing or produced the overtones (even without the complication of the damper pedal being depressed) in the same manner as a piano.
An excerpt from review of the state of the art Yamaha sums this up:
"key-notes Home > The Piano > Yamaha Digital Piano
Yamaha Digital Piano
A Pianist's Review of the AvantGrand
I recently had an opportunity to play the AvantGrand, the new Yamaha digital piano that represents the current state of the art, and wanted to share my experiences with it with key-notes readers.
First, as a classical pianist I must caution that no matter how good digital piano technology gets, nothing replaces the real thing, and I don't see that changing even in the distant future. After all, Stradivarius and Guarneri violins have only become more valuable over time, and the best modern technology has been unable to match the beauty of their sound. Where digital versus acoustic pianos are concerned, a recording of a note (called a "sample") triggered by pressing a key and played by an electronic speaker just isn't the same as a real hammer striking a real string causing a real soundboard to vibrate."
Maybe Classical Pianist are stubborn bastards, too (my wife thinks so of me, but I was stubborn before I took up the Piano, Harpsichord, and Pipe Organ) I don't know of any name Classical Pianist that would perform a recital on a digital piano or have given a product endorsement to date for one (and Yamaha has lots of money. Maybe Classical Pianists aren't endorsement whores, too?)
You also wrote, "I can promise you that we could (and eventually will) shift our focus to modeling the strange things that happen when you push a tube amplifier into the non-linear operating regions."
Tubes aren't all that linear a device to begin with in their "linear" operating regions, and when pushed into distortion and other non-linear regions are even more complicated to understand and chart these variables.
Although the physics of SS components are very well understood, where tubes are concerned, we have a general concept and idea how they work, but being electromechanical devices, no one has fully worked out a complete understanding of why there can be as much variance as demonstrated in a tubes performance, even among tubes of the same dates of manufacture of the same type (12AX7).  (I won't go into component chemical variables, as the late Ken Fisher commented on in a interview)
As I have said previously, (though not in yesterday's post):
How does a tube react to AC signals and at what frequency, and at what voltage, and at what current levels?  (Highly variable.)
Add in transconductance, Mu, internal plate resistances, Miller capacitances, plate currents, as variables, and how tube behaves (or misbehaves) when overdriven (THD and IMD).  
Throw in the minimum voltage below which a tube cannot pull its anode toward the plate and what part of the tubes transfer curve is being utilized at low voltage signals as opposed to high voltage signals (even when controlled by a negative feedback loop) and phase changes from incomplete signal inversions. 
Also toss how a tube reacts to supply voltages which are not rigid (voltage sag) in the power transformer, interaction between the output transformer (and the power tubes): reflected impedance and other factors such as leakage inductance and vice versa), at what point and when an output transformer saturation occur. (I won't even start on the quality or lack there of concerning the Iron used in the laminations. As to the argument over the insulation, Paper or Plastic, anyone?)
These are just a few of the parameters that would have to be quantified, and I am only scratching the surface.
I haven't addressed components as variables, such as capacitors (resistance, as well as inductance, and distortion present in Electrolytic caps), and shan't go to deeply in detail for this evening do to constraints on my time. To  briefly touch on the subject of capacitors, (Dumble builders use ceramic caps) ceramic caps exhibit variation of a capacitor’s impedance with frequency variation. As to a Tweed Bassman model, the carbon composition resistors' resistance on the plates actually varies with the voltage across the resistor.   
And if one is trying to model a specific type of amp, then toss in the speaker cone's behavious, sound pressure levels, open back cabinet/closed back cabinet, room acoustics (standing waves), whether the speaker has an issue of beaming. These vary with signal intensity, signal volume, room temperature, humidity and barometric pressure.
Again, I have only addressed the tip of the iceberg.
If after doing so, one would have to use a Hi-Fi amp with sufficient headroom (lots of Watts) and a neutral full frequency speaker with minimum coloration to the final signal without adding any additional artifacts to the digital ones produced (hopefully at an inaudible level).
I sure wouldn't want to model a Dumble ODS or even  Marshall 800.
The architect Ludwig Mies van der Rohe who said "God is in the details," also said "A chair is a very difficult object. A skyscraper is almost easier. That is why Chippendale is famous."  I wonder what he would have said about linear devices (SS/digital) attempting to replicate a non-linear device (tubes amps)?
Maybe in ten years time the Super Computers of today can be made faster and shrunk in size to eliminate latency (using nano-vacuum tube technology?) to facilitate an economical and super minuscule size to crunch the numbers of these and a host of other variables to facilitate replicating a tube amp and be faster than Damn Fast. (And maybe include random numbers generator to facilitate the randomness of tube behavior?) The price would have to be affordable as 90/10 rule of money applies to Guitarists (as well as keyboard players) too. 
Maybe if all these factors can be digitized, the proof will be in a touch responsive amp that can mimic a tube amp.
Hearing will be believing.
Then again, as my wife points out when see asked why I am writing  this email, "Wouldn't just be easier to use a Tube amp? I use ginger in recipe that calls for ginger."
Best of Luck in your future endeavor.
Steve