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So about that new Si diode clipping in Q5.xx Drive block

spx90

Power User
Thanks a lot @jaresee
am pleased to see that you are working with of the driver blocks :)

I love, historical Muff, I hope there is a big step forward :rolleyes:
 
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FractalAudio

Administrator
Fractal Audio Systems
Moderator
Hey! I had a bunch of time on my hands today. They gave us the day off at work to vote and seeing as I can't vote I took advantage of a house free of kids to play a bunch of guitar. One of the things I did today was broke out the old Analogman-modded TS-9 pedal. It's one of my few remaining pedals. I true gem of a drive pedal.

It was effortless to make the TS-808 pedal and my real TS-9 sound incredibly similar. 60 seconds of tweaking maybe? Scary simple to do now with the default drive block settings and just a little tweak of the low cut (had to cut a bit more than default -- 869.6 Hz) and then nothing by Drive, Tone and Level. Going back and forth between the two they were very, very, very close.

What really blew me away (and I've mentioned this in the mega thread about the firmware release) is the trailing edge of a held note. That's always been where the not-quite-right behavior of the Drive block has been. But now it is deadly accurate. Indistinguishable decay characteristics from my real life pedal now.

I was also very surprised at how close the Drive, Tone and Level knobs corresponded between the real pedal and the Drive block. Not exactly the same, but close enough so that you could start a real world to model match by just putting those three knobs on the model in the same general positions as the real pedal to get you going.
You'll never get the knobs to correspond exactly. Commercial quality potentiometers are terrible. They vary widely in both end-to-end resistance and resistance at midpoint. Variations of +/- 20% are common (that's 40% total!!!). The Axe-Fx always assumes an ideal potentiometer, i.e. a pot where the end-to-end and midpoint resistances are exactly the specified value. Furthermore commercial "audio taper" pots are not truly logarithmic. They use a crude piecewise approximation. The virtual pots in the Axe-Fx are true log.

This is the #1 reason for the whole "no two amps sound the same". In fact they probably do sound the same but you need to adjust the pots on one (and possibly quite a bit) to make it sound like the other. For example if a tone control is at noon (5.00) on one amp you may need to set the other amp to anywhere from 3.00 to 7.00. This applies to any product that uses potentiometers, including drive pedals.

This also means when matching any virtual amp/drive/etc. in the Axe-Fx to a real-world counterpart that you may need to deviate significantly to get the same sound. For example, to get our reference Dual Rectifier's orange channel to match the model I need to set the model's treble control to around 4.0 (with the amp's treble at noon). This is because the pot in the amp has a significant deviation from the intended resistance at the midpoint. It's a 250K linear taper pot but it reads around 100K/150K when set to the midpoint. This is quite typical of commercial quality pots.
 

barhrecords

Axe-Master
You'll never get the knobs to correspond exactly. Commercial quality potentiometers are terrible. They vary widely in both end-to-end resistance and resistance at midpoint. Variations of +/- 20% are common (that's 40% total!!!). The Axe-Fx always assumes an ideal potentiometer, i.e. a pot where the end-to-end and midpoint resistances are exactly the specified value. Furthermore commercial "audio taper" pots are not truly logarithmic. They use a crude piecewise approximation. The virtual pots in the Axe-Fx are true log.

This is the #1 reason for the whole "no two amps sound the same". In fact they probably do sound the same but you need to adjust the pots on one (and possibly quite a bit) to make it sound like the other. For example if a tone control is at noon (5.00) on one amp you may need to set the other amp to anywhere from 3.00 to 7.00. This applies to any product that uses potentiometers, including drive pedals.

This also means when matching any virtual amp/drive/etc. in the Axe-Fx to a real-world counterpart that you may need to deviate significantly to get the same sound. For example, to get our reference Dual Rectifier's orange channel to match the model I need to set the model's treble control to around 4.0 (with the amp's treble at noon). This is because the pot in the amp has a significant deviation from the intended resistance at the midpoint. It's a 250K linear taper pot but it reads around 100K/150K when set to the midpoint. This is quite typical of commercial quality pots.
Is there a reason not to match the reference amps and pedals pots instead of using ideal values?

Seems like the model doesn't exactly match an amp anyway so making the model match the reference amp would not be worse.
 

Smittefar

Fractal Fanatic
@barhrecords It would not help anybody, as it would only match the reference, and everybody's amp will be different. Also, to measure the exact taper, I believe you have to remove the pot from the circuit(soldering)
 

barhrecords

Axe-Master
@barhrecords It would not help anybody, as it would only match the reference, and everybody's amp will be different. Also, to measure the exact taper, I believe you have to remove the pot from the circuit(soldering)
Good point.

I was just thinking about my own amps. The sweet spot on quite a few of my vintage Fenders are close to the same. I bought them all at different times from different places.

I was wondering if most of the amps are not ideal, then matching a reference would put the knobs in a more typical setting (more authentic?)

Anywho, carry on :)
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Good point.

I was just thinking about my own amps. The sweet spot on quite a few of my vintage Fenders are close to the same. I bought them all at different times from different places.

I was wondering if most of the amps are not ideal, then matching a reference would put the knobs in a more typical setting (more authentic?)

Anywho, carry on :)
I don't think you understand.

Let's say the taper of a treble pot is linear. The biggest variation is midpoint resistance, which can vary +/- 20%. On one amp it might be -10%, on the next one off the assembly line it might be +10%. The Axe-Fx assumes 0%. Simple as that. That's what the aggregate is and what the designer originally intended.

When we match to our reference amps we adjust the knobs on the Axe-Fx to compensate for these things. IOW, if our reference amp's treble pot is -10% at the midpoint we reduce the treble knob accordingly on the model when checking the model's accuracy.
 

zenaxe

Fractal Fanatic
You'll never get the knobs to correspond exactly. Commercial quality potentiometers are terrible. They vary widely in both end-to-end resistance and resistance at midpoint. Variations of +/- 20% are common (that's 40% total!!!). The Axe-Fx always assumes an ideal potentiometer, i.e. a pot where the end-to-end and midpoint resistances are exactly the specified value. Furthermore commercial "audio taper" pots are not truly logarithmic. They use a crude piecewise approximation. The virtual pots in the Axe-Fx are true log.
This. Direct experience will bear this all out as truth quickly. Also, just to add: IMHO the fact that highly detailed modelers like the AxeFx can correct things like inconsistencies in values across sweep or imperfection in tapers (there is *no* advantage to piecewise approximation f.ex.) is a direct example of where modelers have the ability to do things you cannot do with physical hardware and in some senses be 'better' than IRL.
 

barhrecords

Axe-Master
I don't think you understand.

Let's say the taper of a treble pot is linear. The biggest variation is midpoint resistance, which can vary +/- 20%. On one amp it might be -10%, on the next one off the assembly line it might be +10%. The Axe-Fx assumes 0%. Simple as that. That's what the aggregate is and what the designer originally intended.

When we match to our reference amps we adjust the knobs on the Axe-Fx to compensate for these things. IOW, if our reference amp's treble pot is -10% at the midpoint we reduce the treble knob accordingly on the model when checking the model's accuracy.
I think I got that but I certainly defer to amp experts over my own knowledge! :)

I wasn't saying the model is not accurate or authentic. They sound incredible and authentic to my ears.

I was just wondering out loud why not make the AxeFx knob positions match the reference amps exactly? Or the drive pedal knob positions match the reference pedals? Even if they are not ideal to the schematic or design.
 

Ed DeGenaro

Experienced
This is why on clean sound we learn how to centre controls on real amps.
In short set them at noon sweep the bass control while ringing a big E chord to its sonic mid point which as Cliff pointed out is somewhere between 10 and 2 o'clock ish. The Do the treble.
Go back to bass since the piston if the treble will influence the bass. Next mud, re adjust treble and bass...that's where your "neutral" center is.
Obviously not working on modified Baxandall tone stacks since bass/treble inversely affecting mids.

In general I like that I can do things on the Axe I can't on Amps and once you start dialing with ears rather than eyes it'll be much less limiting than real amps.
 

spaceranger

Member
I think I got that but I certainly defer to amp experts over my own knowledge! :)

I wasn't saying the model is not accurate or authentic. They sound incredible and authentic to my ears.

I was just wondering out loud why not make the AxeFx knob positions match the reference amps exactly? Or the drive pedal knob positions match the reference pedals? Even if they are not ideal to the schematic or design.
Because he's simulating the circuits and components, not just that one amp. Since the actual performing spec of the components will inherently vary from the published ideal spec, I think what Cliff is doing is establishing a baseline model using the published spec so that the model is better able to simulate other amps of the same make & model, but that will also happen to have inherent variances in their component specs. This allows the model that Cliff produces to be more than just an accurate simulation of one single reference amp, but rather an idealized model that can be more accurately tweaked to match up with any number of the same amps. Then, Cliff tests the idealized model against the reference amp by adjusting the model to match the variances in the components of the reference to check the accuracy of the model.

He's not just trying to reproduce the best one-to-one simulation of that particular reference amp, he's extracting an idealized model of the amp and checking it against the reference amp for accuracy. The point isn't to make a one to one correlation between where you set the controls on the axe-fx and where you set the real controls on that one single reference amp. The point is to make the best model of the circuits and components for ANY amp of that make and model.
 
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JT2

Inspired
I love this [iaresee] TS-9 block. Thank you. But when I disable it in the string the audio goes off. The block must be engaged for sound. What did I do wrong?
 
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