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Amp - true bypass or not?


theredguitar6
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sorry if this one's been covered before.

 

Let's keep it simple and imagine a single signal path with nothing else on it:

Add TWO different amps in series  ( archetype clean + archetype lead ).  set up bypass switches to flick between them - so theoretically each amp is bypassed whilst using the other ..although the signal chain does still pass through the by passed amp in each state.

THIS IS SOUND A ( Preset 1)

Create another preset and do the same thing but pull the second amp block down to a signal loop and put a A/B switch in front.  The A/B is set up 100% A  or 100% B depending which amp you are using.  all amp settings the same 

THIS IS SOUND B ( preset 2)

 

switch between the presets  - VERY DIFFERENT SOUNDS on each amp.

Have i missed something here or does the bypass function not fully bypass - because in example A each bypassed amp is definitely affecting the sound of the active amp.  In my case - actually in a good way.  Kind a sounds the same as putting a buffer in a signal chain.

 

Is this right? 

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I actually went into a support ticket over this subject (I believe we're talking about the same thing) - check the forum for my thread post which I believe was called 'Virtual True Bypass?'

 

They scoped my submitted patches and declared them 'much the same' in the end.

The statement was that it's impossible for a bypassed block to affect the sound downstream.

 

My ears insist this isn't the case, and I'm pretty sure they didn't plug in a guitar to test with a plain old ear test.

 

Please have a look at my thread to confirm that we're essentially talking about the same thing - though I didn't to the parallel routing because my patch is complex enough to not allow that - instead I had to keep them serial.

HOWEVER - I did make a work-around, gig tested this past weekend; I used a stereo effects loop pair (1/2) into which I inserted my own custom made short jumper cables straight from in to out, and did a hardware bypass of the second downstream amp when I wanted it out of the signal path using the separate send and return blocks on either side of the 2nd/downstream amp.

I'd meant to go back to that thread and update it with this 'workaround.'

 

What I found was it changed massively when I went from one amp to a different one in the downstream position; I had been using an ANGL downstream, tamed down greatly, but the Litigator coming into the equation was a better fit for what I was looking for, so I swapped it in a copy of the patch. Then compared... and was shocked by the difference, especially when using IRs instead of cab/mic blocks.

 

I can say this, too; for some reason, the audible difference to my ear is greatly reduced in this most recent firmware update (as it happens; couldn't be in response to my ticket, since there was too much overlap of time).

 

 

I hadn't intended on revisiting this can of worms; I had determined to 'agree to disagree' with the findings I was presented with... but your posting shows that it's likely not just me and my good friend Fulcrum hearing the difference.

He heard it instantly when I demonstrated it to him.

 

 

Thanks for posting.

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Nope don't understand that...

The split is 100% A or B ...not in the middle so it should not halve the signal

 

Is that the split or the merge.

Just checking all the boxes. But if you have the split set to Split A/B split 100, yes, you're right, it shouldn't halve the signal.

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Is that the split or the merge.

Just checking all the boxes. But if you have the split set to Split A/B split 100, yes, you're right, it shouldn't halve the signal.

No it's definitely the the split at A100/B100 ...so it shoudn't affect the signal.

I think  that the amp blocks - even when bypassed affect the signal chain- slight lift in level and perceived brightness.

I'm going to do further experiments 

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One thing is that when you create a split path, each path is automatically attenuated by 3dB, with the thought being that the summed output of those paths would be equal in volume to the original path. So when you have two parallel paths and select between one or the other, that will be 3dB quieter than having the two amp blocks in series with each other and selecting one or the other. I'm not sure where the 3dB cut actually takes place in the signal flow, but if it's at the split block itself, that actually could cause a slight tonal difference through the amp blocks.

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Did the OP see my post, and the suggestion to read my post about this subject?

 

I'm glad this can of worms has been re-opened in some fashion..

yes i did ... and many thanks for your thoughts and suggestions. I'm absolutely 100% sure on this so i'm to do some more work on it and report back.

Whilst we're on the subject i also have 2 identical presets ( by accident actually) apart from one has a parametric just before the output. So they should both sound the same if the para is bypassed right? ... well the don't. It's subtle but the para adds a little more mid and less HF even when it's bypassed.  Which is weird because thats what it's actually there to do. ...but not when it's bypassed.

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One thing is that when you create a split path, each path is automatically attenuated by 3dB, with the thought being that the summed output of those paths would be equal in volume to the original path. So when you have two parallel paths and select between one or the other, that will be 3dB quieter than having the two amp blocks in series with each other and selecting one or the other. I'm not sure where the 3dB cut actually takes place in the signal flow, but if it's at the split block itself, that actually could cause a slight tonal difference through the amp blocks.

Good call...

hadn't realised that.

I'll have a play around and restore that 3db with some gain blocks.  That a least will restore the perceived vol drop....and may indeed brighten the amp by pushing a little more. 

I should say that actually i'm very happy with the sound i'm getting switching the amps in series.  Just puzzled by what's going on  ...i know a lot of folk prefer the two amp A/B switch scenario for operational reasons. 

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Mystery solved .... or at least dramatically improved.

It's not the A/B split that causes the problem ...it's the merge mixer!.   We've taken a whole bunch of measurements this morning ( i'm in the pro audio industry) and the merge mixer is dropping 3-4db in the signal chain.  If you have a reasonable number of effects etc after this ( even reverb) it has quite a dramatic effect on tone and dynamics. Fortunately this all came back by raising the A & B levels on the merge mixer by 3db  ( 3.5db on a clean amp).

I did try some other tests - putting 3db gain block in front of the amps ( or A/B split) and that just slightly compresses the amps - last thing i wanted.

Also made up some presets to see if amps in series affect each other when bypassed.  It's small.  but the merge mixer affect is BIG.

I think this may have repercussions on other things as well ...  anywhere a merge mixer is used.

Hmmm ...

Hope that helps - it's certainly cured my issue.

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Mystery solved .... or at least dramatically improved.

It's not the A/B split that causes the problem ...it's the merge mixer!.   We've taken a whole bunch of measurements this morning ( i'm in the pro audio industry) and the merge mixer is dropping 3-4db in the signal chain.  If you have a reasonable number of effects etc after this ( even reverb) it has quite a dramatic effect on tone and dynamics. Fortunately this all came back by raising the A & B levels on the merge mixer by 3db  ( 3.5db on a clean amp).

I did try some other tests - putting 3db gain block in front of the amps ( or A/B split) and that just slightly compresses the amps - last thing i wanted.

Also made up some presets to see if amps in series affect each other when bypassed.  It's small.  but the merge mixer affect is BIG.

I think this may have repercussions on other things as well ...  anywhere a merge mixer is used.

Hmmm ...

Hope that helps - it's certainly cured my issue.

 

Well, that's a whole bunch of useful data - I'm going to make note of all of this and do some more testing of my own (though I am not equipped to do measurements with anything more than my ears.... but at least those were good enough to tell me something was amiss in the first place...)

 

In my super-patch, there are two split/merge points - one after each amp, as I use 2 cabs merged, plus on path 1 I have some parallel effects after the split (chorus and phaser) ...

Though, for me, that was my base-line sound, and it was sounding as it should for me.

My issues cropped up only after I changed the 2nd/downstream path 2 amp from ANGL to Litigator for my higher-gain sound option, and found that the result of the main clean sound with the 1st/upstream path 1 amp and cabs running past the downstream amp and cabs was hobbled in some fashion sound-wise.

Much as you described above; dynamics and tone in general negatively affected...

 

Thanks for digging into this.

I'm hoping Line 6 is monitoring this thread; it adds data points to my support ticket, as I see it.

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