Question about Split A/B and Merge block levels

[stephane_dupont]

Hello,

 

There's something that I don't understand with "A/B" and "Merge" block levels.

 

Let me explain:

 

Let's say I have a straight signal, from guitar to XLR outputs, no block on the signal, nothing. A blank preset.

 

Now, I add a 0db gain block, just to be able to split path (If I'm right, we can't split path without a block?). Still the same, the sound has not changed.

 

Now, if I click on the 0db gain block and move it below, a "Split" and a "Merge" blocks are created.

 

If I configure the blocks like that:

 

Split: Split A/B, Route To "A 100"

Merge: 0db / Center / 0db / Center / Normal / 0db

 

I should have the same sound than the blank preset from the start right? It should go from the input, to the split block, 100% of the signal is sent on the A path, there's no block on it, then the merge is with everything center and 0db, the output should be the same as a blank preset right?

 

... but it's not the case. It's less loud. I recorded both to test it thoroughly (first recorded dry guitar, then reamping with straight path and then with the split/merge): with the split/merge blocks, there's exactly 3db less.

 

Bug or feature? If it's a feature, can you explain it? :)

 

Thank you.

 

 

[duncann]

Right, can't split without something there to cause the split.

 

If this is accurate - no reason to really doubt you - it's a nice discovery. Something to certainly be aware of when designing patches because everything downstream from the split can potentially be tonally different because of this, unless compensated for. Would also like to know if this a bug or intentional.

[hideout]

I'm wondering if it's intentional to prevent overloading blocks downstream.

 

I still think you should be able to create splits without having to instantiate a block.

[zooey]

Forgive my probable ignorance here, don't have a Helix yet, but bear with me for a second.

 

If you split a signal into two separate unity gain paths, then sum them together, it'd end up louder, because you're adding two copies of the signal together, an increase of 3db. You'd have to reduce the level at the summer by 3db to get the same level you started with.

 

If instead of splitting the signal, you had an A/B switcher, where only one side of the split is live at a time, that doesn't happen. It's unity gain into the split, unity gain back at the summer, so it's unity gain through the whole chain.

 

From the name 'Split A/B' (which is all I know about it), maybe that block is designed to be used as either an A/B switcher (one side live at a time), or a true split (both sides always live). If that's the case, either it or the summer needs to have its gain adjusted differently for those two cases. It's not exactly a bug or a feature, it's physics, or maths, really.

 

Make sense?

[duncann]

But stephane_dupont observed and measured 3dB less.

 

An A/B split can be used to route the signal to either path A, path B, evenly, or anything in between.

 

A Y split just splits the signal, no parameters to adjust.

[Joepeggio]

Hello,

 

There's something that I don't understand with "A/B" and "Merge" block levels.

 

Let me explain:

 

Let's say I have a straight signal, from guitar to XLR outputs, no block on the signal, nothing. A blank preset.

 

Now, I add a 0db gain block, just to be able to split path (If I'm right, we can't split path without a block?). Still the same, the sound has not changed.

 

Now, if I click on the 0db gain block and move it below, a "Split" and a "Merge" blocks are created.

 

If I configure the blocks like that:

 

Split: Split A/B, Route To "A 100"

Merge: 0db / Center / 0db / Center / Normal / 0db

 

I should have the same sound than the blank preset from the start right? It should go from the input, to the split block, 100% of the signal is sent on the A path, there's no block on it, then the merge is with everything center and 0db, the output should be the same as a blank preset right?

 

... but it's not the case. It's less loud. I recorded both to test it thoroughly (first recorded dry guitar, then reamping with straight path and then with the split/merge): with the split/merge blocks, there's exactly 3db less.

 

Bug or feature? If it's a feature, can you explain it? :)

 

Thank you.

Like stated above a merge of 2 excact signals produces a 3db increase. I think the A/B and y splits reduce the level by 3db so when they re-merge its back to unity. The A100 setting etc is the percentage to that side, still 3db lower it seems.

 

I have ran into this in some patches. I usually boost it in the merge, boost the level of a block in that path, or put a 3db boost before the split if there is a gain sensitive block downline.

[stephane_dupont]

Also, it's really strange that an A/B split reduce levels by 3db, but a Y split doesn't...

 

If someone from Line6 can give us more details that would be great.

 

EDIT: my bad, Split also reduce level by 3db.

[zooey]

Thinking about this more, I think another thing involed here is the pan law in the split, exactly how the left and right levels change a you change balance control. There's no one right answer, and some fancy consoles let you change it to your liking, but clearly it's important here. If the amount each channel is attenuated when the blaance control is centered.doesn't line up with the same thing on the merge, you could get behavior like this.

 

Try this: Pan the signal all the way to one side, and do the same test. It wouldn't suprise me if the level drop went away. Maybe not, but it'd be an interesting test.

 

L6 kind of does need to chime in at this level.

[spikey]

Also, it's really strange that an A/B split reduce levels by 3db, but a Y split doesn't...

 

If someone from Line6 can give us more details that would be great.

 

EDIT: my bad, Split also reduce level by 3db.

Hummm... Every 3db down is power cut by half, with 3db gain being the opposite. I wonder myself why this is there (A/B split) I.E. whats its purpose for reducing by 3db,  and how would you use it?

[Joepeggio]

The default of a split is to remerge before the output, therefore recombining the dry signal getting the level back to the original. Any other way can be compensated for by adjusting the level somewhere (anywhere) in the path as needed.

 

Seems logical and real world to me. Sort of how analog works. Me being an Android / windows guy, I get frustrated when a band mate tries recording us using Logic on his Mac and it starts trying to predict what we want to do.

[vxjoe]

A splitter in real life does have a 3db loss, while a switch a/b does not. Summing two identical signals also has a 3db gain. One cannot get any more real than that.

[spikey]

The default of a split is to remerge before the output, therefore recombining the dry signal getting the level back to the original. 

 

Well that answers my question then- thanks...

[spikey]

A splitter in real life does have a 3db loss, while a switch a/b does not. Summing two identical signals also has a 3db gain. One cannot get any more real than that.

 

But Not all splitters are 3 db down. Some are 7, others 10 etc etc... But a "two way" is most likely like you state, 3 db....  :P

[mykejb]

On a "real" pedalboard though a split often used to be a couple of bits of wire and three plugs and no buffer/gain change.

 

If the split blocks do change the gain maybe at some point that might become configurable so you can set the gain reduction/boost independently for each output. Same with the merge.

 

Mike

[stephane_dupont]

In any case, it would be great to see the behavior confirmed here by someone from Line 6, and maybe add a few words about it in the manual?

[tagmusenmagnus1]

Well. It has to take of the 3dBs as a standard, doesn't it - Otherwise you wouldnt be able to use a Controller assign on the split block without the blocks on path A changing sound when you go fra "A100" to anything less what "A100". 

Or am I not right ? 

[stephane_dupont]

So no one from Line 6 can confirm us the exact behavior? I thought here was the best place to ask, but shall I create a support ticket instead?

[perapera]

you could find this helpful :

cheers
Lorenzo

 

 

Edited June 20, 2019 by perapera
I edited this post because the first version contained an error, sorry