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Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-15 11:33:20.7050

Looking for help here, looks like lots of other people are very confused about this, too.

Of course I understand the concept of dual signal paths and stereo guitar rigs, but the way that the virtual mixer block is integrated into the system is not intuitive at all.

Basically, I'm a single/mono amp guy. Looking to create a simple signal path of guitar->stomp boxes->amp->reverbs/delays etc.->physical outputs

Sounds simple enough, right? But I've already discovered that it's not so simple.

First, regardless of where you place the mixer block, the dual input choices in the utilities screen will both feed whatever your first virtual block is, be it fx, amp, mixer, etc. If you select 1.Guitar 2.Same (seems to be the default setting for most presets) then you are effectively doubling your guitar signal's strength before it even hits the first block (and I love L6's advice here - "lower your instrument's volume"...I won't go on the obvious rant here but we all know most guitar players like to ride their volume pots high for tonal reasons). I use a Strat so I didn't have the distortion/fizz problem that a lot of humbucker players have described, but I did notice that all the presets - even when I disabled all the glossy effects and stripped down to amp/spkr/mic - sounded too gainy and compressed.

Setting input two to "mic" did make an instant improvement, but still not where I thought it should be in terms of realism and dynamic range. Plus, now I got the mic input's hiss in the sound.

Next, I moved the amp AFTER the mixer block and reduced input B's level to mute on the mixer block. I figured that would solve everything except the nice option of one day later using the mixer block at some other point in the chain (or doing parallel input paths like compressors etc).

Again, noticeable improvement instantly, so I must be doing something right. Then it occurred to me that if I set path A's pan to center, that should theoretically get as close to a mono guitar->stomps->amp as you can get.

Trouble is, how do I know which option is unity gain? Leaving A panned 100% definitely provides a cleaner input signal, but is that signal -3dB, or is that some kind of default/unity gain, and center panned signal is actually +3dB? I see no point in spending $500 on this thing if I can't even replicate the signal path of, say, plugging the guitar straight into the amp model without any artificial gain staging in between.

Re: Can't Understand the HD Mixer Block!
by phil_m on 2011-06-15 13:27:36.4160

As far as the input settings, why don't you set the second input to Variax instead of mic? Then you'll won't have to worry about the mic preamp giving you any extra noise.

As far as the mixer block itself, the one thing you've discovered that I've mentioned a few times here is that the pan control isn't really a pan as much as it is a balance. So if you have it set to center, you have two signals, the left and the right, for that tone at 100% volume. When you have it set hard right or left, you only have one signal at 100% volume. So, in reality, they are both unity gain, it's just depends on what you're doing as far as mono and stereo effects is. If you're not using stereo effects, and you are running in mono, hard panning will give you unity gain. The only "danger" in hard panning is if you put a stereo effect after the amp but before the mixer block. Other than that you should be fine.

Re: Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-15 14:01:36.7040

Thanks to phil_m for the quick response but it didn't completely apply to me...some have commented that you can set input 2 to Variax, which seems like it works, but the kidney bean HD 500 doesn't have this option.

I just spent some more time with it. Maybe this was obvious to others, but I just spent an hour A/B-ing some test ideas and I figured this out.

As we all know, inputs 1 and 2 are summed to mono if you put any mono FX or a single amp block in pre-mixer block position...this is straight from the L6 manual, and my tests confirm it. This creates all kinds of problems/questions about just exactly how you can be sure you're getting unity gain into a mono path amp model's input. When you fire up the HD for the first time and play around with some dry amp sounds to test the realism, how do you know if you're hitting the pre/drive section of the amp with a "clean" guitar (unity gain) signal? Otherwise you can never be sure where any unwanted compression is coming from in the tone.

What they don't tell you in so many words is, you can create a parallel path DIRECTLY from the inputs simply by moving the amp and pre-amp effects into a SINGLE parallel path chain. No special voodoo here, just grab them as "move" blocks and fiddle with the direction buttons until you get both your amp and pre-amp FX blocks as follows: 1. pre-mixer, and 2. on the same parallel path (top path, for example). At this point, the hypothetical parallel amp #2 will be shown on the edit screen blacked out as "disabled".

So, what you have now is the following:

1. Input 1 (guitar) feeding whatever effects and amp block you have on that path (top path) and finally into the mixer...which is effectively exactly a complete mono path with a unity gain input from guitar all the way to the amp's input, with the only gain staging being what you want it to be (e.g. an overdrive pedal in between guitar and amp)

2. Input 2 (guitar or mic, doesn't really matter for this example) feeding the bottom parallel path through a disabled amp and into the mixer.

Then you just reduce gain on mixer path B all the way down to "mute", and set gain on path A to 0 dB and pan path A to center. Now you can be sure you have unity gain all the way through your chain (except your amp settings, of course) - and more importantly, you can be sure that you are effectively re-creating the same signal path as if you plugged your guitar straight into stomp boxes and then into the amp input, as with a normal guitar rig.

Also, whatever stereo effects you put towards the end of the chain AFTER the mixer block (and mono effects that may happen to be immediately after the mixer, like, say, LA-2A) will still be stereo output (albeit fed by a mono source - mixer path A panned center). This is effectively the Bradshaw/Lukather/Van Halen setup from the 80' can have ping-pong delays, or modulations, or whatever stereo effects you want leaping back and forth between monitors/headphones L and R.

On the other hand, be aware that if you put a stereo output effect POST amp but PRE mixer, then you will be feeding that effect's stereo input B from your bottom parallel path (w/ disabled amp), so if you have path B's gain set to mute, you won't be able to hear the left output of the stereo effect (you'll just be hearing the right side panned mono, but panning is a separate issue in this scenario). If you raise the mixer's path B volume in this scenario so you can hear the stereo effect, you'll be hearing the sound of the DRY guitar's other channel feeding the effect's processing path. So in one side you'll hear the sound of the amp feeding one channel of the stereo effect, and in the other side you'll hear dry guitar feeding same effect (could be cool, but probably not!) - unless you enable amp B, which is fine, but that may or may not be what you wanted, plus having both amps enabled is a real DSP hog).

But back to the main long as Amp B is left disabled, you're not eating any extra DSP by doing it this way, as far as I can tell. Remember if you enable Amp B to test some dual amp sounds, you won't hear the 2nd amp unless you unmute it in the mixer block.

This is REALLY un-intuitive. Guitar players aren't used to thinking like this. I didn't figure it out until it hit me that the dual input paths are making their way through the signal chain whether I like it or not and whether my preferred way of setting up a chain can handle it or not. When you look at the edit screen, if you want a standard, conventional mono path, it just seems logical to arrange the blocks as a straight mono path and let the mixer be wherever seems most convenient. But the way the inputs are set up won't allow this to work the way you think it does.

Geez, why don't they just put a "Guitar-MONO" option in the input selection indicator which automatically disables the 2nd path???? Doesn't that seem so much more logical? Kudos to Line 6 for making a great product, but people's ability to use simple logic and effective communication is generally getting worse by the year. Thank your local Teacher's Union for making sure that at least 3 generations of Americans have now managed to make it through our public school systems without ever learning how to think critically or communicate ideas effectively.

Re: Can't Understand the HD Mixer Block!
by Mincer on 2011-06-15 18:54:39.5540

This is one of the best explainations so far of the 'mono/stereo' mixer problem. Would it be possible to post a few sample patches so we can see graphically (in the editor) what is going on?

I know 1/4" outputs sum to mono when one is used, but XLRs are incapable of this feature. You can always use a direct box from the 1/4" out, or have 2 sets of patches- one for 'stereo' editing or recording, and one for live use, with both sides panned left. Both are pretty inelegant solutions.

Re: Can't Understand the HD Mixer Block!
by Pezza on 2011-06-16 02:11:18.7250

Thanks for making more sense of the over complicated HD500 routing! I think there should be a default 1 input setting (with the first part of the chain mono until you use a stereo fx). Surely only a small minority of users are using both inputs - maybe with the JTV or to use a mic. Most people will be plugging one guitar into the input and don't want to be worrying about signal doubling.

As it is, for a mono set up, I agree you're best using one input and placing your fx/amp on one side of the parallel routing then set the mixer 'balance' to the centre and mute the other side.

For a dual amp set up with mono fx before the amp you also need to use 1 input and put the mono fx in the first series section feeding both amps. If you use both inputs you double up on the signal into the mono fx with undesirable results (usually).

For a dual amp set up with no mono fx infront of the amp you have to use both inputs or you'll lose one amp.

The annoying part comes when you want to use a mono fx infront of dual amps and turn the fx off/on. You'll have to use both inputs (to get dual amps working when fx off) and so the fx is being given a double signal - very poor.

Line 6 don't even seem to understand it, which is why many of the presets sound bad - they're feeding both inputs (second input set to 'same') into amps/fx and feeding them a double guitar signal. Guitarists spend a lot of time/money getting the output level of their pickups as they want it - they don't want that level screwed up the second they plug it into their amp (modeller).

I do love the HD500 but wish the flexibility hadn't made this aspect so awkward/un-intuitive to use.

Re: Can't Understand the HD Mixer Block!
by phil_m on 2011-06-16 06:19:31.1960

Well, you have to split the signal going to dual amps somehow. It's not much different than if you had an actual dual amp in the real world. You have to think through these signal routing issues and come up with what you want to do. There's no silver bullet solution because everyone wants to do something a little different. I don't see what's being described as a bug or flaw, really, it's just that it could be described with a bit more clarity in the manuals. In the real world, if you wanted to put a mono effect before dual amps, you'd have to figure out how to split the signal after the mono effect. I believe on the HD500 if you put a stereo effect after a mono effect but before the dual amps, you can split the signal going into the amp without having to have the second input on.

Personally, I think too big of a deal is being made about the signal doubling. It is an issue for some people, but there are probably a lot of people who won't even notice it. A 3dB boost won't have that detrimental of an effect on a lot of pickups.

Re: Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-16 13:40:37.1760

Well, we agree that you do have the split the signal somehow, but the frustration out there is with the fact the OS forces you to split the signal at all if you don't want to. As I said, guitarists don't naturally think like that since it's not how we're used to seeing our gear set up, and the fact that L6 is well known to be staffed with guitar players is a little curious. I think everybody's wondering WTF, how did they not see that this was going to confuse and frustrate most of the people who use it? Is everyone a L6 a metalhead who just wants to hear gobs of preamp saturation? (no disrespect to metalheads intended, I love metal, I just don't/can't play in that style much).

Assuming this can be addressed in firmware (and I don't know for sure that it can), the fix is really easy:

1. Inputs screen in utilities section - offer a Guitar/MONO option for input 1. Selecting this option automatically greys out any options for input 2. Make this the default setting for all presets that would be simplified and benefit from it.

2. If the user later tries to activate any mono FX or amp block pre-mixer, one of two options kicks in:

a) an alert screen pops up , "You must de-select mono input in utilities to use this parallel signal path" or

b) the signal path is automatically reset to stereo inputs in the preset's utilities section. This may leave the user scratching their head why the sound isn't the same if they later switch back to single path/amp, but that's a slightly different matter.


Again with all due respect for a great product and great value overall, the fact that forums all over the net are abuzz with complaints about this issue indicates strongly that lots of musicians are noticing it. Saying that 3 dB isn't that much difference is like saying a million dollars is a lot of money - depends on the context - esp. since a "decibel" isn't necessarily really a specific electrical voltage reading anyway; 3dB means different things in different contexts (dBv, dBu, etc.). I certainly noticed it, and it created a bad first impression for me. The whole reason I stepped up to HD was to get that real, live, not overly compressed amp feel, and for the first few hours and days I was playing around with the sounds, I knew something was just not quite right.

I did RTFM before I drew any hasty conclusions, but the relationship between physical inputs 1 and 2 and mixer channels A and B is really not explained at all. And 95% of guitar players want to plug in and play a rig configuration that makes sense to what we're used to, real world. Having a klugey input section that is not immediately intuitive is a more serious problem than L6 evidently wants to acknowledge, even though yes, agreed, it's not an actual "defect" per se.

If L6 is indeed competing with the Avid11 or Fractal Axe-Fx units, then they need to make sure the HD's put their best foot forward right out of the box. I almost sent mine back for a refund; my impression kept coming back to, "Yeah, it sounds good...but for some reason I can't quite put my finger on yet, it doesn't sound great". Already owning an XT and having all those tones well dialed in over the years, the HD had to be great to justify retiring my XT.

Now, with the gain staging set properly, the HD blows the XT away. No contest. And the difference really is night and day vs. HD out of the box, I swear. When I now play the JTM45 and Hiwatt models through headphones for a half hour, my whole body's equilibrium is thrown off for the next hour or so, like I was sitting in the front row for the actual Live at Leeds concert (well, nothing could be that good, really, but since I'll never see the real Who live, this has to be my next best thing). These amp models really push some air like the real amps did, and they don't mush up and back away from your attack the way most other simulators do. Fantastic.

Re: Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-16 13:43:29.7050

You spotted the weakness in my idea, I didn't even think about that until you said it. There are several work-arounds, each with pros/cons.

I agree with you on all points!

We shouldn't need a "work-around", though, it's a really weird input setup.

Re: Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-16 13:52:21.5550

I'm traveling on business all week so uploading a preset isn't an option for me right now, but I'll try to next week.

But basically, if you want to use my idea, just make sure that you arrange the (pre-mixer) amp and FX blocks so that the signal flow line is split to parallel at the very start - at the far left of the edit screen. AND, all (pre-mixer) FX and amp blocks are on that same path.

Then, make sure the other path's amp block is disabled.

Then, set the mixer channel A to 0 dB level (you can adjust to taste later) and pan center.

Set channel B level to mute (otherwise you'll hear the dry guitar coming into your sound unless you have input 2 set to mic in utilities). Pan B is kind of irrelevant in this scenario unless you later activate amp B. If you do activate amp B later, make sure your utilities input settings are 1. Guitar, 2. Guitar or Same. If 2 is set to mic, your guitar won't feed into amp B at all.

Re: Can't Understand the HD Mixer Block!
by phil_m on 2011-06-16 14:34:12.5050

Actually, I may have to take back what I said earlier about it not being described well enough in the manual - I just took a look at the Advanced Guide for the bean, and it's described pretty well.

The page 3 options allow you to select either the “GUITAR” or “MIC” physical inputs to be used as the “Source” Inputs 1 and/or 2. These settings are saved per Preset.
About Source Input Signal Routing: It is important to note how POD HD actually routes Source Inputs 1 and 2 through Amp & FX Blocks that are positioned “Pre” position. The following behaviors apply:

• In a configuration with no Amp or FX Blocks in Pre, Input 1 is fed only to Path A and Input 2 only to Path B. Therefore, this is the best configuration if you want to retain discrete Input Sources into Paths A & B.
• Placing an Amp Block or an active mono FX Model in Pre results in a “summing” of Input Sources 1 & 2, feeding the same, combined signal into these Pre-positioned Models, and thus into each Path A & B. You may need to adjust your instrument’s volume level to avoid overloading your Pre-positioned Amp or FX Models.
• Placing a Stereo FX Model in Pre results in the left channel FX output being fed to Path A and its right output to Path B.*
• The Mixer Block’s Volume and Pan options provide independent control for Path A & B outputs before they are fed through any Blocks positioned “Post” the Mixer.
• By setting Input 2 to “Same,” this effectively routes your Input Source to both stereo Paths A & B (which is how you can feed one guitar input into two Amp Models and/or parallel FX, for example).

It doesn't outright say that you'd want to mute Path B for a true mono path. I don't think that this level of complexity is too much to expect for a device that offers as much as the Bean or the HD500. Let's not forget that for those who don't want to deal with it, there's always the HD300 or 400.

Re: Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-16 15:17:20.1240

Ok, ok, ok.

I read that same section 3 or 4 times before posting originally. Will come back to that in a second.

It doesn't change the fact that the default "out of the box" summed inputs are unintuitive and create extra noise and potentially unwanted gain. All I was saying is, seems like in a company full of guitar players, someone would have thought of this. It's a well known axiom now that less gain = bigger sound. Excessive preamp saturation = more compression = thinning tone.

Having said that, my original question was, how do you know what unity gain actually is?, and I appreciate your ideas and thoughts on that. It occurred to me today that I also could have disabled both amps, listened to dry guitar, and isolated for all variables until I figured it all out. But who wants to do that?

The problem with that manual section you reference is that when it describes the summing effect, it recommends turning down your "instrument's" volume to compensate. Most musicians using this unit will be guitarists. When you turn down your guitar's volume pot, you usually lose some tone and responsiveness. Some pots and circuits are less prone to this effect than others, but all passive electric guitars suffer from this to some degree. Surely L6 must know that. So turning down your volume pot is a terrible suggestion for most players.

I don't want to niggle over a borderline insufficient manual description. Life moves on. But lots of HD500 users clearly don't like this input setup, and denying that it's a valid criticism only makes these users frustrated.

Saying "well, that's what the 300 and 400 are for" is a little flippant. I got the HD500 because I wanted a desktop config. and all 8 effects blocks, esp. after I read that reverb, vol, LA-2A, gate, and wah each use up a block (the old XT gives you all these as "freebies" in your chain, leaving 3 more blocks available). So the 300 and 400 didn't fit the bill for me; you could eat up your whole chain with the basics and not have any blocks left for a mod or filter or delay.

I gotta move on here, no more posting on this for me, have spent enough time on this. But thanks for the input (no pun intended).

Re: Can't Understand the HD Mixer Block!
by Tony-N on 2011-06-17 10:58:20.7480

I'm currently waiting for the POD HD to hit the retailers here in Sweden, so I downloaded the manual to read it beforehand and have it all kind of figured out when the unit comes.

No strange things at all, as expected, except for this more than slightly confusing signal routing from the inputs...

I have to agree with cwlivingston, they sure have made it more complicated than it should be. Having a true mono setup available as a "default" seems like a better starting place for most guitarists instead of this advanced routing.

This actually made me hesitate to buy the Bean, even though I'm not afraid of having to figure out signal routings and other problems.

Thanks to cwlivingston for taking time to experiment and inform us about about the findings...

Re: Can't Understand the HD Mixer Block!
by cwlivingston on 2011-06-17 11:33:37.6000

Glad to help. Wish L6 weren't being so unresponsive on this issue. They seem to feel that we're pouting about something insignificant.

Once you get your gain staging set, though, it is a great sounding modeler. I haven't tried the Avid11 or AxeFx so I can't compare, but I'm not a pro guitarist anymore and $1000+ for a guitar product isn't in the budget. For $500 the HD is a big winner.

Re: Can't Understand the HD Mixer Block!
by stumpsout on 2011-06-18 15:38:01.5210

+1 Much appreciate you sharing this info..very helpful to my understanding of this.

Re: Can't Understand the HD Mixer Block!
by stumpsout on 2011-06-18 23:42:02.1190

I believe this is what a starting patch would look like from your description.

I just used a default J-45 as an example.

Re: Can't Understand the HD Mixer Block!
by Dbourget on 2011-06-20 18:20:52.0760

This has been a very interesting discussion, If possible, I'd like to see an actual patch from start to finish if possible so I can really understand what's going on.


Re: Can't Understand the HD Mixer Block!
by perapera on 2013-01-02 20:14:49.5360

hi cwlivingston

I know this thread is old, but anyway I wanted to advise you and anyone interested to read another thread I started:

here you can find some answers to your questions just by following the signal flow on the graphs I drew and reading the description I wrote below them

please read it and only after reading that come back here and read this:

your setup with only path-A active has nothing wrong but is by no means different from other setups obtaining exactly the same gain staging and stereo-mono routing

for example if you set:

- guitar/same as the two inputs

- mixer channel-A level to unity and pan to center and path-B to mute

these four setups give you exactly the same gain and "mono-to-stereo" panning:

<a target=new href=" class="jive-image" src=""/><a target=new href=" class="jive-image" src=""/><a target=new href=" class="jive-image" src=""/><a target=new href=" class="jive-image" src=""/>

also with this last setup, if you set:

- guitar/same as the two inputs

- mixer channel-A and B levels to unity and pan hard left and right

you get the same result in a fifth way.

notice that this fifth way is exactly the default "new tone" blank patch (with guitar/same instead ov everything/same as input selection);

see here:



The information above may not be current, and you should direct questions to the current forum or review the manual.