Thaks a lot Nigel for your info. It is in my plan to improve my actual Leslie simulator, and I had listen a lot of rumors about this VENTILATOR and also BURN (by Scognamiglio, another Italian that you may know) and I was impressed because I also think thatn nowadays there cant be any incredible technology under the hood for a leslie, but maybe a big bag of tricks.
Ciao M. > -----Messaggio originale----- > Da: music-dsp-boun...@music.columbia.edu [mailto:music-dsp- > boun...@music.columbia.edu] Per conto di Nigel Redmon > Inviato: mercoledì 18 giugno 2014 11:25 > A: A discussion list for music-related DSP > Oggetto: Re: [music-dsp] Simulating Valve Amps > > BTW, I do know that it was developed with the Sonic Core SCOPE SDK, and I > suspect its just using fairly routine DSP blocks, with a lot of care in tweaking > the sound. (It runs in my mind that I might have seen some block diagrams > on a forum back when he was developing itthe point is that I dont think > there is any cutting-edge tech involved.) But thats all I know. > > On Jun 18, 2014, at 10:40 AM, Nigel Redmon <earle...@earlevel.com> wrote: > > > No, Marco, sorry. I wish I did. The result is very good, and a huge > > leap from the sim in the CX-3. Very annoying that they dont support > > MIDI switching of the speed > > > > http://www.earlevel.com/main/2013/02/16/ventilator-adapter-in-a-mint-t > > in/ > > > > > > On Jun 18, 2014, at 10:11 AM, Marco Lo Monaco > <marco.lomon...@teletu.it> wrote: > > > >> Ciao Nigel, talking about the VENTILATOR, do you know something more > >> about its secrets/internals? > >> :) > >> > >> M. > >> > >>> -----Messaggio originale----- > >>> Da: music-dsp-boun...@music.columbia.edu [mailto:music-dsp- > >>> boun...@music.columbia.edu] Per conto di Nigel Redmon > >>> Inviato: mercoledì 18 giugno 2014 08:22 > >>> A: A discussion list for music-related DSP > >>> Oggetto: Re: [music-dsp] Simulating Valve Amps > >>> > >>> Well, some people think its close enough for rock n rock (amp > >>> sims), > >> others > >>> dont. Its the same with analog synths and virtual analog. But > >>> theres > >> also > >>> the comfort of tube amps, and theres the comfort of the limited > >>> sound palette of using the amp that you know and love. Amp sims are > >>> really about variety (cant afford a Plexi, a Twin Reverb, SLO, > >>> AC-30, and a few > >> boutique > >>> amps? Now you can). > >>> > >>> I appreciate the old stuff, but I appreciate the convenience and > >> flexibility of > >>> the new stuffto me it *is* close enough for rock n roll (new stuff > >>> in generalI dont play much guitar). I play a B3 clone because I > >>> hauled a Hammond decades ago, and I hauled and still have (needs > >>> work) a Leslie, > >> but > >>> Id just as soon use my Ventilator pedal on the CX-3 (yes, with > >> programmable > >>> leakiness and aging of the tone wheels, etc.)more convenient, and > >>> gets the sound I want. Others would shudder at the thought. Well, > >>> until their backs start giving out I know a hardcore, old-time B3 > >>> blues player > >> (Mule > >>> a nickname he earning for hauling around his B3 and Leslies) who > >>> picked up > >> a > >>> clone for his aging back after hearing my CX-3 though the > >>> Ventilator. Not > >> for > >>> all gigs, mind you, but as an option to go with for some gigs. The > >>> point > >> is that > >>> if the tradeoffs are attractive enough, its easier to let yourself > >>> try > >> new things > >>> even if you feel that it falls ever so slightly short of what youre > >>> used > >> to, or > >>> strays from your comfort zone. > >>> > >>> So while some might feel that amp sims havent arrived yet, other > >>> might > >> feel, > >>> where the heck have you been the past decade?" ;-) > >>> > >>> > >>> On Jun 17, 2014, at 6:59 PM, robert bristow-johnson > >>> <r...@audioimagination.com> wrote: > >>> > >>>> On 6/17/14 8:24 PM, Nigel Redmon wrote: > >>>>> (Thinking outside the nest ) > >>>>> > >>>>>> (...maybe that means opening up the LPF as the gain knob setting > >>>>>> is > >>>>>> reduced) > >>>>> Yes > >>>>> > >>>>> And good discussion elsewhere in there, thanks Robert. > >>>>> > >>>> yer welcome, i guess. > >>>> > >>>> you may be thinking outside the nest; i'm just thinking out loud. > >>>> > >>>> i think, like a multieffects box, we oughta be able to simulate all > >> these amps > >>> (don't forget the Mesa Boogie) and their different settings in a > >>> single > >> DSP > >>> box with enough MIPS and a lotta oversampling. dunno if simulating > >>> the > >>> 50/60 Hz hum and shot noise would be good or not (i know of a B3 > >>> emulation that simulates the "din" of all 60-whatever keys leaking > >>> into the mix even when they're all key-up). but they oughta be able > >>> to model each deterministic thing: the power supply sag, changing > >>> bias points, > >> hysteresis in > >>> transformers, capacitance in feedback around a non-linear element > >>> (might use Euler's forward differences in doing that), whatever. > >>> whatever it is, > >> if > >>> you take out the hum and shot noise, it's a deterministic function > >>> of > >> solely > >>> the guitar input and the knob settings, and if we can land human > >>> beings on the moon, we oughta be able to figure out what that > >>> deterministic function is. for each amp model. it shouldn't be > >>> more mystical than that (but > >> there > >>> *is* a sorta mysticism with musicians about this old analog gear > >>> that we > >> just > >>> cannot adequately mimic). > >>>> > >>>> and thanks to you, Nigel. > >>>> > >>>> L8r, > >>>> > >>>> r b-j > >>>> > >>>> > >>>>> On Jun 17, 2014, at 4:07 PM, robert bristow- > >>> johnson<r...@audioimagination.com> wrote: > >>>>>> On 6/17/14 3:30 PM, Nigel Redmon wrote: > >>>>>>> This is getting nesty... > >>>>>> yah 'vell, vot 'r ya gonna do? :-) > >>>>>> > >>>>>>> On Jun 17, 2014, at 10:42 AM, robert bristow- > >>> johnson<r...@audioimagination.com> wrote: > >>>>>>> > >>>>>>>> On 6/17/14 12:57 PM, Nigel Redmon wrote: > >>>>>>>>> On Jun 17, 2014, at 9:09 AM, robert bristow- > >>> johnson<r...@audioimagination.com> wrote: > >>>>>>>>> > >>>>>>>>>> On 6/17/14 5:30 AM, Nigel Redmon wrote: > >>>>>>>>>> > >>>>>>>> ... > >>>>>>>>>>> Anyway, just keep in mind that the particular classic amps > >>>>>>>>>>> dont sound "better" simply because they are analog. They > >>>>>>>>>>> sound better because over the decades theyve been around, > >>>>>>>>>>> they survivedbecause they do sound good. There are > plenty > >>>>>>>>>>> of awful sounding analog guitar amps (and compressors, and > >>>>>>>>>>> preamps, > >>>>>>>>>>> and ) that didnt last because they didnt sound > >>>>>>>>>>> particularly good. Then, the modeling amp has the > >>>>>>>>>>> disadvantage that they are usually employed to recreate a > >>>>>>>>>>> classic amp exactly. So the best they can do is break even in > sound, then win in versatility. > >>>>>>>>>>> And an AC-30 or Matchless preset on a modeler that doesnt > >>>>>>>>>>> sound exactly like the amp it models loses > >>>>>>>>>>> automaticallyeven if it sounds better because it failed to > >>>>>>>>>>> hit the target. (And it doesnt helped that amps of the same > >>>>>>>>>>> model dont necessarily sound the same. At Line 6, we would > >>>>>>>>>>> borrow a coveted ampone that belonged to a major artist > and > >>>>>>>>>>> was highly regarded, for instance, or one that was rented > >>>>>>>>>>> out for sessions because it was known to sound awesome.) > >>>>>>>>>> what did you guys do with the amps when you > borrowed/rented > >>> them? was your analysis jig just input/output, or did you put a few > >>> high- impedance taps inside at strategic places and record those > >>> signals simultaneously? > >>>>>>>>> Yes. For instance, sweeping the EQ with incremental settings > >>> changes. > >>>>>>>>> > >>>>>>>> yes, another issue (which i didn't really touch on) is mapping > >>>>>>>> the > >>> settings of the knob to the internal (to the DSP) coefficients and > >> threshold > >>> values and such. that is "coefficient cooking" and is the same > >>> issue as defining Q in EQs so that the knob behaves like the ol' > >>> Pultec or > >> whatever. > >>> your digital implementation might work very well, but if the > >>> position of > >> the > >>> knob in the emulation is not nearly the same as it was for the > >>> venerable > >> old > >>> gear (to get the same sound), someone might complain. > >>>>>>> Oh yes, they *will* complain ;-) > >>>>>>> > >>>>>>>>>>> On Tue, Jun 17, 2014 at 6:58 PM, Nigel > >>> Redmon<earle...@earlevel.com> wrote: > >>>>>>>>>>>> On Jun 16, 2014, at 7:51 PM, robert bristow-johnson< > >>>>>>>>>>>> r...@audioimagination.com> wrote: > >>>>>>>>>>>>>> one thing that is hard to replicate is a sample rate that > >>>>>>>>>>>>>> is infinity (which is how i understand continuous-time > >>>>>>>>>>>>>> signals to be). but i don't think you should need to > >>>>>>>>>>>>>> have such a high sample rate. one thing we know is that > >>>>>>>>>>>>>> for *polynomial > >>>>>>>>>>>>>> curves* (which are mathematical abstractions and maybe > >>> have > >>>>>>>>>>>>>> nothing to do with tube curves), that for a bandwidth of > >>>>>>>>>>>>>> B in the input and a polynomial curve of order N, the > >>>>>>>>>>>>>> highest generated frequency is N*B so the sample rate > >>>>>>>>>>>>>> should be at > >>> least (N+1)*B to prevent any of these generated images from aliasing > >>> down to below the original B. > >>>>>>>>>>>>>> if you can prevent that, you can filter out any of the > >>>>>>>>>>>>>> aliased components and downsample to a sample rate > >>> sufficient for B (which is at least 2*B). > >>>>>>>>>>>>>> > >>>>>>>>>>>>> This really goes out the window when youre modeling > amps, > >>>>>>>>>>>>> though. The order of the polynomial is too high to > >>>>>>>>>>>>> implement practically (that is, you wont end up utilizing > >>>>>>>>>>>>> the oversampling rate necessary to follow it), > >>>>>>>>>> this is a curious statement *outside* of the case of hard > >> clipping. > >>> oversample by 4x and you can do a 7th-order polynomial curve and > >>> later eliminate all of the aliasing. oversample by 8x and it's > >>> 15th-order. do > >> *no* > >>> oversampling and you can still make use of the fact that there's not > >>> a lot above 5 kHz in a guitar and amp (so 48 kHz is sorta > >>> oversampled to begin with). you can fit a quite curvy curve with a 7th- > order polynomial. > >>>>>>>>>> > >>>>>>>>>>>>> so > >>>>>>>>>>>>> you still be dealing with aliasing. Modern high gain amps > >>>>>>>>>>>>> have huge gain > >>>>>>>>>>>>> *after* saturation. In practical terms, you round into it > >>>>>>>>>>>>> (with a polynomial, for instance), then just hard clip > >>>>>>>>>>>>> from there on out, and there goes your polynomial (it can > >>>>>>>>>>>>> be replaced by an approximation that's very high order, > >>>>>>>>>>>>> but whats > >>> the point). > >>>>>>>>>> yes, we splice a constant function against a curve. if at > >>>>>>>>>> the > >> splice as > >>> many possible derivatives are zero as possible, that splice appears > >>> pretty seamless. this is why i had earlier (on this list) been > >>> plugging these > >> curves: > >>>>>>>>>> > >>>>>>>>>> x > >>>>>>>>>> f(x) = C * integral{ (1 - u^2)^M du } > >>>>>>>>>> 0 > >>>>>>>>>> > >>>>>>>>>> (C gets adjusted so that f(1) = 1 and f(-1) = -1.) > >>>>>>>>>> > >>>>>>>>>> you can splice that to flat values at +/- 1 and the nature of > >>>>>>>>>> the > >>> function will not change appreciably from the polynomial in the > >>> region of > >> the > >>> splice. > >>>>>>>>>> > >>>>>>>>>> anyway, the whole point is to give the guys with golden ears > >>>>>>>>>> no > >>> cause to complain about hearing aliases. same with emulating > >>> sawtooths > >> and > >>> hard-sync synthesis. > >>>>>>>>>> > >>>>>>>>>>>>> Anyway, you pay your money, you make your choices. > >>> Obviously > >>>>>>>>>>>>> some really good musicians making really interesting music > >>>>>>>>>>>>> use modeling amps. They dont have to be better than > >>>>>>>>>>>>> tubes, in order to be a win, just good enough to be worth > >>>>>>>>>>>>> all the benefits. If youre a session music, you can bring > >>>>>>>>>>>>> in the truck with all of the kinds of amps that might be > >>>>>>>>>>>>> called on, or you can bring a modeling amp, for instance. > >>>>>>>>>>>>> And going direct into the PA or your recoding > >>>>>>>>>>>>> equipment etc. Im not > >>> going to make judgments on what people should like, so Ill leave it > >>> at > >> that. > >>>>>>>>>>>>> > >>>>>>>>>>>>> One happy thing about the aliasing is that, given a decent > >>>>>>>>>>>>> level of oversampling, it wont be bad at lower overdrive > >>>>>>>>>>>>> levels. At the higher the overdrive levels, the harder it > >>>>>>>>>>>>> is to hear aliasing through all that harmonic distortion > >>>>>>>>>>>>> youre > >>> generating. So it could be worse... > >>>>>>>>>> i really agree with this, Nigel. with *some* oversampling > >>>>>>>>>> (but > >>> theoretically not sufficient oversampling), you can get away with a > >>> lot > >> (like > >>> hard limits or whatever stuff goes on inside a transformer with core > >> loss). i > >>> would not say that you have to oversample to a ridiculously high > >>> degree > >> just > >>> because there is a hard-limit saturation in there or that your tube > >>> model > >> is > >>> not a polynomial approximation (but i wonder why you wouldn't try to > >>> fit > >> the > >>> grid-to-plate tube curve to a finite-order polynomial). > >>>>>>>>> What I mean is... for a modern high-gain amp, the gain is on > >>>>>>>>> the > >>> order of 2^16 (and the curve starts its significant bend up near > >>> 1). So > >> most of > >>> the signal, when youre playing maxed out, is simply clipping hard. > >>> If > >> your > >>> goal is to not alias in the audio band at all, by figuring the max > >> harmonic > >>> component based on the order of the equivalent polynomial and the > >>> highest freq of the guitar input coming in well, your oversampling > >>> factor is going > >> to > >>> be a lot higher that youre willing to implement. > >>>>>>>> i understand. hard-hard-limit and you got harmonics going up > >>>>>>>> to > >>> infinity anyway. > >>>>>>>> > >>>>>>>>> Theres really no point in calculating a continuous polynomial > >> over > >>> that range that I can see. > >>>>>>>> well, if it splices *well* to the clip region, it might *still* > >>>>>>>> have > >> a point. > >>>>>>>> > >>>>>>>>> Its no big dealI just brought it up because I often see > >>>>>>>>> people, > >> here > >>> and elsewhere, go down the thought path of... "OK, I want to make a > >>> guitar distortion unit if I keep my polynomial to order N, I only > >>> need to > >> oversample > >>> by (N+1)/2...", completely forgetting that when, in their code, they > >> branch to > >>> limit the output to +/- 1, their polynomial order just went out the > >> window. > >>>>>>>> yes, that's true (sorta). at least *if* the splice to the > >>>>>>>> limited > >> constant > >>> value is not smooth. > >>>>>>>> > >>>>>>>> but you can make a polynomial match as many derivatives (equal > >>>>>>>> to > >>> zero) of the hard limit as possible (but that might be at > >>> cross-purposes > >> to > >>> getting the polynomial to follow a tube curve) and for levels that > >>> hit > >> that limit > >>> (so the code branches to the limit), if the overflow or spike isn't > >>> so > >> bad, the > >>> behavior isn't so far away from the "ideal" polynomial and the total > >>> behavioral issue remains inside the window, i would think. > >>>>>>> Yes, Robert but, with the kind of gain necessary OK, so you have > >>>>>>> the > >>> y-xis as you output level, x-axis as input. To view the entire curve > >>> for a Soldano Super Lead Overdrive, for instance, you draw the curve > >>> of your choice to rise from y=0 and give you a soft bend into y=1 (full > output). > >> The > >>> bend will be somewhere around x=1, ballpark (maybe its x=2 or 3, to > >>> allow for lower input levels, but the point is that its a small > >>> number compared > >> to > >>> whats coming next) then you allow for x=30000 or so (a flatline > >>> from the > >>> x=1..3 area). Is that not a pretty high order polynomial? > >>>>>> well, yeah, and it might better be described as a function that > >>>>>> is > >>> discontinuous with most of its derivatives, even the 1st. > >>>>>> > >>>>>> so > >>>>>> > >>>>>>> The point being, yes the polynomial would be handy at low gain > >>> settings, but you still need to build this thing to work at extreme > >>> gain > >> settings > >>> at the same time. > >>>>>> okay, you mean with it cranked up so that it virtually hard limits. > >> that's > >>> not exactly what comes to mind about "warm" tube distortion. like > >>> those DevilDrive guys (or was it the Kemper guys) built a 12AX7 > >>> preamp to model (and i wonder how much that tells us about how a > >>> Fender Twin Reverb cranked up to arcweld behaves like). > >>>>>> > >>>>>> but this is hard clipping distortion, not zero-crossing > >>>>>> distortion, > >> right? in > >>> between the nasty hard limits, you might be able to decently model > >>> the > >> tube > >>> curves with finite-order polynomials. specifically the mapping > >>> curve from biased grid voltage to biased plate voltage given a > >>> specific load line > >> (which > >>> may be affected by power sag). maybe you can cover that quite well > >>> with a finite-order polynomial and emulate that with a finite > >>> sampling rate. but > >> if it > >>> clips, might be nasty, regarding aliases. > >>>>>> > >>>>>> the only thing i know how to tame down a hard limit (and it may > >>>>>> very > >>> well not be compatible with the characteristic tube curve) is to set > >>> as > >> many > >>> derivatives as possible to zero and splice the hard limit to that thing. > >>> continuity to the 2M-th derivative including the hard limit. > >>>>>> > >>>>>>> So anything at the low gain settings is pretty insignificant for > >> something > >>> designed to handle the high gain settings. > >>>>>> well, we gotta think sorta like the string theorists. we gotta > >> imagine how > >>> to seamlessly glue together two ostensibly incompatible systems. > >>> like how do we crossfade from the low-gain behavior (the "warm tube > >>> sound") to the behavior we like when it's cranked up to arc-weld? > >>>>>> > >>>>>> > >>>>>>> Hence my feeling that there not much point to calculating how > >>>>>>> much > >>> headroom you haveyou can pretty much count on infinity. There may > >>> be some reasons to do itIm not demanding that I have the right > >>> idea, just simply explaining what I meant by my comments. In > >>> reality, its not so > >> clear > >>> cut, because as I mention before, the more you get into a situation > >>> where aliasing will be big, at the same time you are in a situation > >>> where youll > >> have > >>> more generated harmonics to mask the aliasing. In the end, aliasing > >>> is > >>> *mainly* a problem if you bend a guitar note and you heard harmonics > >>> going in the wrong direction. For some reason guitarists just cant > >>> get around > >> that > >>> (lol). > >>>>>>> > >>>>>>>>> BTW, the more the overdrive, the less the weaker upper > >>>>>>>>> harmonics > >>> of your guitar matter, so you can cheat by rolling them off as you > >> increase > >>> drive. > >>>>>>>> a useful idea. more pre-LPF as the grunge gets cranked up. > >>>>>>>> > >>>>>>>>> But you cant rely on that too much, because guitar players > >>>>>>>>> like to hang analog distortion stomp boxes in front of your > >>>>>>>>> modeling amp, giving you powerful higher harmonics. :-) > >>>>>>>> yeah, but can't you *still* pre-LPF that signal (the output of > >>>>>>>> the > >>> distortion stomp box) as the amp drive is cranked up? i dunno. > >>>>>>> Yes, its definitely one place where you can win, and help > >>>>>>> yourself make the best of a practical amount of frequency > >>>>>>> headroom. Probably the biggest difference (between assuming > >>>>>>> direct, clean guitar strings as input, and one thats be > >>>>>>> pre-crunchified with a > >>>>>>> stompbox) is that for the former you might get by with a > >>>>>>> lower-order filter, because guitar string harmonics drops of > >>>>>>> pretty quickly by themselves. (So, you might design an amp sim > >>>>>>> that seems relatively alias-free, then get a customer or beta > >>>>>>> tester complaining about the aliasing, and that's were you find > >>>>>>> out that guitarists will still want to run their stuff into your > >>>>>>> sim, even if you give them those functions in DSP.) > >>>>>> well, i know there can be different specs. but for a 32-tap FIR > >>>>>> LPF, > >> you > >>> can put the same brick-wall LPF on both guitar (that might not need > >>> it as > >> bad) > >>> and the grunge box. it's just that for clean amp setting, you might > >>> hear > >> the > >>> difference between your straight-grunge pedal and the LPF'd one (and > >>> it's less necessary, maybe that means opening up the LPF as the gain > >>> knob setting is reduced). > >>>>>> > >>>>>> -- > >>>>>> > >>>>>> r b-j r...@audioimagination.com > >>>>>> > >>>>>> "Imagination is more important than knowledge." > >>>> > >>>> > >>>> -- > >>>> dupswapdrop -- the music-dsp mailing list and website: > >>>> subscription info, FAQ, source code archive, list archive, book > >>>> reviews, dsp links http://music.columbia.edu/cmc/music-dsp > >>>> http://music.columbia.edu/mailman/listinfo/music-dsp > >>> > >>> -- > >>> dupswapdrop -- the music-dsp mailing list and website: > >>> subscription info, FAQ, source code archive, list archive, book > >>> reviews, > >> dsp > >>> links http://music.columbia.edu/cmc/music-dsp > >>> http://music.columbia.edu/mailman/listinfo/music-dsp > >> > >> -- > >> dupswapdrop -- the music-dsp mailing list and website: > >> subscription info, FAQ, source code archive, list archive, book > >> reviews, dsp links http://music.columbia.edu/cmc/music-dsp > >> http://music.columbia.edu/mailman/listinfo/music-dsp > > > > -- > > dupswapdrop -- the music-dsp mailing list and website: > > subscription info, FAQ, source code archive, list archive, book > > reviews, dsp links http://music.columbia.edu/cmc/music-dsp > > http://music.columbia.edu/mailman/listinfo/music-dsp > > -- > dupswapdrop -- the music-dsp mailing list and website: > subscription info, FAQ, source code archive, list archive, book reviews, dsp > links http://music.columbia.edu/cmc/music-dsp > http://music.columbia.edu/mailman/listinfo/music-dsp -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp
