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Pod HD Dual Cab research/setlist

meambobbo

Member
Messages
493
from the L6 forum:
http://line6.com/support/thread/88099

For those who have followed my work with the Pod HD, you know that I have often used "dual cabs" in my patches. For those who don't, see here to catch up: http://foobazaar.com/podhd/toneGuide/cabsMics#dualCab - basically I'm using the same amp in a dual amp patch but varying the cab/mic used in each channel. I combine a "bright cab" with a "dark cab" to get a consistent, high-quality frequency response from the uber-lows to ultra-highs.

A big part of dialing in these tones revolves around one cab/mic being out-of-phase with the other. Previously, I used two crude methods to work-around this issue: either find combinations that seemed to be in-phase, or try adding a neutral EQ or two to one Channel only to see if it improved the tone. Today, I present you a solid set of research data that more accurately demonstrates and rectifies the issue.

But first, here is a small sample of my research applied to a HD 500 setlist. Notice the tone is consistent and rich throughout the entire frequency spectrum. I cannot get close to this quality of tone with a single amp/cab. If you can, I'd like to see your patch.
http://foobazaar.com/podhd/toneGuide/dualCabs.h5s

This is just the tip of the iceberg. I plan to complete this setlist with other cabs serving as the "bright cab" other than the Tread V-30 and 57 on axis. I also want to make multiple setlists for each of the high gain amps. I also want to add the Marshall T75 cab. I want everyone who enjoys high gain to hear what the Pod HD is truly capable of.

The naming convention for each patch is "2_X_Ym_Zn" where 2 means dual cab setlist, X means amp used, Y means cabinet in Channel A, m means mic in Channel A, Z means cabinet in Channel B, and n means mic in Channel B. For instance, the first patch is "2_R_R-_R/" - this means dual cab setlist, Rectifier amp, Rectifier cab with 57 on axis mic in Channel A, Rectifier cab with 57 off axis mic in Channel B. Below lists all possibilities for the legend:

Amps
J - JCM-800
R - Rectifier
U - Uberschall
F - Fireball

Cabs
R - Tread V-30
H - Hiway
X - XXL
G - Greenbacks
U - Uber

Mics
- - 57 on axis
/ - 57 off axis
9 - 409 Dyn
2 - 421 Dyn
4 - 4038 Ribbon
1 - 121 Ribbon
6 - 67 Cond
8 - 87 Cond

There are 3 links below. The first is a spreadsheet with a matrix of every possible combination of cab/mic with another, for the Tread V-30, Hiway, XXL, Greenbacks, and Uber 4x12 cabs with all available mics with the delay required to make them in-phase represented in a number of samples assuming a 96 kHZ sample rate. The second is a list of relatively tone-transparent effects, the settings I used for my research, and the delay time in samples the effect adds to the signal. The third is a list of a combination of effects, useful to get liquidity from the second link.
http://foobazaar.com/podhd/toneGuide/CabsDelayTimes.xlsx
http://foobazaar.com/podhd/toneGuide/FXDelayTimes.xlsx
http://foobazaar.com/podhd/toneGuide/FXCombinationDelayTimes.xlsx

So here's how to apply this knowledge. First look up any pair of cab/mic you want to use with any other cab/mic in the CabDelayTimes spreadsheet. Channel A's cab/mic is listed on the x axis, Channel B on the Y axis. Where these rows and columns meet, you'll see a number. That tells you the number of samples you need to delay Channel B to get phase correction. If the number is negative, that means you need to apply the delay to Channel A (if so, it might be simpler to simply switch the cab/mic in Channel B to Channel A and vice versa).

Once you have found the delay number, you need to add effects to channels A and B to get the specified delay. You'll notice in the FXDelayTimes spreadsheet, the smallest delay time for any effect is 6 samples. To get values less than that you need to add a larger delay to one Channel and a shorter delay to the other Channel. For instance, to get a 4 sample delay in Channel B, you'd put a Parameter EQ in Channel A and a Blue Comp in Channel B. This puts 10 samples in Channel B and 6 sample in Channel A, giving you a difference of 4 samples in Channel B. This is where the FXCombinationDelayTimes spreadsheet is useful - you can quickly look up combinations that will yield delay samples in increments of 1 sample from 1 to 20+.

A few notes:
Even with phase correction, the bass can get a bit woofy sounding if you dial in bass on both cabinets. I set the Low Cut Cab DEP to around 50% (260 HZ) on my "bright cab" to prevent having both too much bass and it sounding a bit "off". The bass is going to sound cleaner and tighter from the "dark cab" anyway.

On my "dark cab", I find even with phase correction, the mixed high ends sound kinda fake together, especially when using different mics. So I generally set the amp's Treble control to 0% on my "dark cab".

Most of the compressors additionally include a LP filter. This is quite evident when they are applied to whichever channel you use as your "bright cab". Thus, I try to avoid using them to delay the signal on my "bright cab". If I need to use one to get the specified phase correction in my document, I just ignore that and get as close as I can using an EQ or something that definitely won't kill my high end. For instance, if I need an 8 sample delay, the closest is the Vetta Juice at 7.5 samples, but I instead use a Mid-Focus EQ with 6.5 samples. On my "dark" cab, this is not an issue. I'm ok with dialing out the high-end there, and will use whatever gets me closest to the research.

Many cab/mic combinations are currently impractical. Using 3-4 effects to achieve phase correction is a huge drain on DSP and effect blocks. I hope my research isn't the end result, but a starting point for individuals to realize how powerful the onboard cab/mic sims can be if they could be dialed in as mentioned. The real end-game is for Line 6 to implement a feature to be able to delay each channel on the Mixer block by samples in increments of 1 from 0-60. This would require a buffer maximum of 60 samples, which at 24 bits is only 180 bytes of memory. It should require little to no DSP, similar to the Volume effect. Then any dual cab combination would become practical, even when using some DSP-expensive effects.

Related threads:
Feature Request
http://line6.com/support/message/390465

TheGearPage Thread about Pod HD timing
https://www.thegearpage.net/board/index.php?threads/1138483

TheGearPage thread discussing the same effect delay phenomenon
https://www.thegearpage.net/board/index.php?threads/964530
 

Jim Soloway

Member
Messages
14,623
Just a really quick and dirty test using two Flip Tops, one with a 1x12 Celestion and the other with a 2x12 Blackface double and the results are amazing. And I haven't even begun to tweak the mics and deep amp and speaker settings. Now the question is whether there are enough resources left to build an entire patch this way.

The whole thing never ceases to amaze me. It's like having a really great amp that there are an infinite ways t make even better. It is just so cool.
 

meambobbo

Member
Messages
493
hey jim - thanks for the response - let me know which cabs and mics you usually use - i'll fire up the white noise tonight and make a patch to try to see what makes them sound most in-phase.

DSP is a big issue, which is why I have several requests I want Line 6 to do. The following would greatly help with DSP:

1) mono versions of reverb effects
2) separating amp and cab/mic choices into different blocks, so you can do one amp into two cabs or vice versa
3) incorporating delay times into the Mixer block so that you don't need to use EQ's or compressors to the get the delays necessary to sync up different cab/mics.
 

Jim Soloway

Member
Messages
14,623
I added trem and verb and immediately hit the DSP wall. Too bad. This had real promise. On the other hand I've made a couple more small tweaks to my main Flip Top patch and it sounds better than ever so I can't be too unhappy.
 

meambobbo

Member
Messages
493
yessir - DSP is tight. My main use case for this was a metal rhythm tone, where no verb is necessary. I found that's where it's most necessary - you can't get a solid low end to searing high end frequency response without something sounding washed out on a single-amp/cab patch.

Sometimes I can fit verb in my patches if I'm very frugal about effects. But sometimes I replace it with a delay or two. In the worst case scenario I'll use E.R.
 

drock2k1

Silver Supporting Member
Messages
798
This is fantastic. It unfortunately means that I may have to get my dirt from boxes but still, the tones available...wow
 

mpr

Member
Messages
789
Thanks for the digging into all this. I don't have a Pod, but maybe eventually. :)

Processing power limitations aside, is this accurate enough now to solve all the problems you were having with dual cabs?

What's "first freq approaching -infinity in Hz"? And what kind of noise does the loop add?
 

rufedges

Member
Messages
1,267
Not enough DSP for me to try dual cabs.........I definitely have to have my reverb and delay as well.......prefer my current setup with the presets acting as stomp boxes on/off and not as complete amp changes, so,......would like to try it, but I am good right now.
 

lespaulidas

Member
Messages
69
Holy crap!

I just ran your setlist on my HD500>>DT50 rig, and I was blown away! Killer tones Meambobbo! Works great with the dream rig.

I am loving the Treadplate amps you have setup. They sound so good and play great! Currently running it via Line6 Link to my DT50 in full power mode at 2 O'clock with Attenuator for low volume. They sound killer as is and I expected I would have to switch them to PRE's, but they sound so good now as is!

I'm going to play around some more with it and change the amps up and check that out, but I'd definitely be curious to see what else you come up with.

Thanks Meambobbo!
 

meambobbo

Member
Messages
493
Not enough DSP for me to try dual cabs.........I definitely have to have my reverb and delay as well.......prefer my current setup with the presets acting as stomp boxes on/off and not as complete amp changes, so,......would like to try it, but I am good right now.
Well as I mentioned above there are some relatively simple things line 6 could implement to make dual cabs much less dsp intensive. But they're not going to listen to just me. I need people to stand beside me begging for these features. Running a single amp into dual cabs and using a sample based delay instead of eqs to delay either channel would be far less dsp expensive than the patches I set up. Try out the setlist and if you love the tone, help me bug line 6 to get the features added. Let's have our dual cabs and our verb too!
 

meambobbo

Member
Messages
493
Thanks for the digging into all this. I don't have a Pod, but maybe eventually. :)

Processing power limitations aside, is this accurate enough now to solve all the problems you were having with dual cabs?

What's "first freq approaching -infinity in Hz"? And what kind of noise does the loop add?
I originally never had real "problems" with dual cabs - I found them to be a solution to the original problem which was that any single onboard cab/mic simulation left me wanting a bit more - either the highs were washed out or the bass wasn't tight and powerful enough. EQ'ing them didn't help. So dual cabs was the solution, and many combinations being out-of-phase was a restraint, not a constant issue. It meant I had to choose pairs of cab/mic's that worked well together without compensating them. I basically was trying to find such, ruling out most combinations as initially unusable. After a while I noticed other combinations plus an EQ in channel A or B would make them sound better than the first ones I found. So then I thought I'm getting phase correction, but maybe I'm only getting partial phase correction. With more refined tools, I could make them sound even better. So I did so in my DAW using spectrum analysis. Then I did the same with various "tone-transparent" effects. And some math later, I came up with the research presented above, and turned it into the setlist as a proof-of-concept. I'm loving the tones I can get now, with a wide variety of cabs and mics to choose from, rather than being constrained to certain combinations.

Is this the be-all-end-all? NO! In some cases, you need 3 EQ/Compressors to achieve phase correction. That's ~18% of the unit's DSP. A variable delay feature would take up ~1% DSP. combined with being able to run 1 amp model to 2 cabs, I estimate an additional 12-20% DSP savings. In total, we could have our dual cab tones plus an addtional ~29 - 37% DSP. That's huge. That basically makes it capable of advanced effect chains with dual cabs. Pitch Glide (whammy), smart harmony, spring reverbs would then be available. If i had that much DSP to work with, I'd never ask for any more. The Pod still wouldn't be an Axe II, but I couldn't justify the +$2000 difference (after adding a floorboard) for a few more amp models and ability to use more effects - I also don't think the quality difference is that significant.

what I mean by first frequency approaching negative infinity is that in a classic comb filter where the same signal is mixed with itself, only one of the signals is delayed, certain frequencies regularly spaced through the frequency spectrum are perfectly canceled. That's kind of what's occurring here. I use the first canceled frequency to determine the exact amount of delay that an effect introduces. See the wikipedia entry for the formula.

Some cab/mics are delayed more than other cab/mics. Thus, mixing them creates a comb filter. The EQ/compressor introduces delay to the signal, and when done in the right amounts, prevents the comb filter from occurring. I used a spectrum analyzer to find the canceled frequencies for effects. This allowed me to find how much the Pod HD delayed the signal for each effect. For the cab/mic combinations, I used Voxengo Sound Delay to test a variety of delays for each pair until I found where the signal was strongest and least freq cancellation was occurring. Then I figured out what combination of effects in the Pod would create the same approximate amount of delay and made my setlist above.
 

meambobbo

Member
Messages
493
hey I know a lot of you said you would rule this out because DSP is so tight, but I went back this morning and was able to add a reverb to most of the patches. Some I couldn't, but I could put delay. For a few, I can fit delay AND reverb. I'm going to always add those when I can to the patches, and I'll indicate if a patch has delay/reverb with a 'd' or 'r' or both at the end of the patch name. also, if you want a bit more space, there's always the E.R. control, although I do prefer reverb.

I haven't uploaded the improved setlist yet. I'll probably work on it a bunch this weekend, and fill it up. Then I'll move on to JCM, Uber, and Fireball versions.
 

mpr

Member
Messages
789
meambobbo, what sort of the noise does the FX loop add? Is it bad enough to make general FX loop usage undesirable?
 

meambobbo

Member
Messages
493
meambobbo, what sort of the noise does the FX loop add? Is it bad enough to make general FX loop usage undesirable?
it adds a slight noise increase - this is to be expected considering you're doing an extra set of D/A A/D conversions. if you boost the signal before the loop, the issue isn't as bad, so it's worse early in the chain rather than after amp models or compressors, etc. some have complained that its unusuable the noise is so bad. i think that's a stretch. i find it's not bad at all. most people i've heard from agree, many of whom use the 4 cable method as their main rig.

i only have an external wah pedal which i run in front of the pod. I don't 4 cable method or anything like that. I only use it to add delay to the signal or force mono summing when there's no DSP for anything else. So my uses are pretty rare, but I don't avoid using it as though it was a big tonal sacrifice.

also, some have said there's a volume drop across the pod hd as well as from the loop. i haven't tested that, but I think it may be accurate. however, it's not a dealbreaker - just compensate inside the many volume controls inside the Pod's signal chain.
 

drock2k1

Silver Supporting Member
Messages
798
I hope to get a few good patches with this over the weekend. I use my HD500 every week live and this could be a game changer for me. I, like most others, will probably need to introduce some external pedals but an overdrive and maybe a reverb shouldn't be too hard to throw in a bag with the HD500
 

meambobbo

Member
Messages
493
as i said earlier today, you can reliably put one each of an OD, EQ, and reverb effect into most of the patches in the set list, without taking away the EQ/compressor(s) I use for phase correction. Some you can fit reverb and delay, in addition to an OD and EQ. The worst offenders you have to settle for OD, EQ, and a delay. Compressors and EQ take up a little less than 6% of DSP each, so it's not that bad.

Also, the Noise Gate effect takes up very little DSP. Volume/Pan effects and the FX loop are like 1% DSP or less.

Also, the exact effect you use matters. Spring reverb is basically twice as expensive as the other reverbs. I like the Chamber, but boost the decay time and keep it pretty low mix. And I usually use Digital Delay, but sometimes have to use Ping Pong delay - you can set it so that there's no ping pong effect and it works like a normal delay.

edit - i'll upload the new version of the setlist as soon as i get home - it has the max delay/reverb you can have, using reverb over delay when only one fits. I'll add a gate up front too.
 
Last edited:

drock2k1

Silver Supporting Member
Messages
798
If I can squeeze in a Digital Delay I would be elated. I will post back what I found worked well. I don't know how much it will help but I think increasing the amount of people in the think tank can only help. I will put in a feature request with L6 for dual cabs.

EDIT- Feature request submitted
 






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