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dual cab setlist/research
by meambobbo on 2012-09-27 07:43:17

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

Thisis 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

style="text-decoration: line-through;">http://foobazaar.com/podhd/toneGuide/FXDelayTimes.xlsx

style="text-decoration: line-through;">http://foobazaar.com/podhd/toneGuide/FXCombinationDelayTimes.xlsx

EDIT:The links below replace those above.  See my last post in this thread for more details on changes.

Online Google Sheets version:

https://docs.google.com/spreadsheet/ccc?key=0AsSFadRSa9zYdG1kc1J2b1ZvRFVlUVIydXRMVVoyZnc&usp=sharing

Downloadable Excel version:

http://foobazaar.com/podhd/toneGuide/CabsDelayTimes_V3.xlsx

Sohere'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

TheGearPageThread about Pod HD timing

http://www.thegearpage.net/board/showthread.php?t=1138483

TheGearPagethread discussing the same effect delay phenomenon

http://www.thegearpage.net/board/showthread.php?t=964530

Edit:Some have mentioned possibly making this adjustment automatic in a feature request.  I agree.  Some effects even change their delay value, making it impossible to be manually synced.

the pitch glide is the craziest example.  when you turn it on it's at a certain number of samples, but as you use it, the exact delay changes.  so if it's at unison and there's 20 sample delay, then you move it up an octave and back to unison, now the delay might be like 30 samples.

the mid-focus eq also seems to have slight variation of its delay as you move the LP freq and Q.

i think the best case fix would be a system setting that can be set either to auto or manual or mixed.  auto would behave as you describe - the two channels are automatically synced.  manual is straight sample-based delays adjustible on either channel as i originally described.  mixed would automatically update the values, but you could set it to be always at a certain amount out of sync.

The way auto would work is it would sum the total delay in samples for each channel in real time depending on the effect, amp, and cab/mic choices.  Whichever channel had the least latency would have latency added to match the other channel.  This would occur in real-time, so that toggling effects on/off, or changing parameters would not cause the channels to become out of sync.

i think all modes would be important because when mixing certain cab/mics, some people may find the comb filter effect to be pleasing, reducing some harsh high-end.  So manual/mixed would be as valuable as auto to these people.  and some people may even want to toggle effects on/off to engage/disengage the comb filter, so they'd prefer manual over mixed.



Re: dual cab setlist/research
by drock2k1 on 2012-09-28 10:23:30

Just want to say that these findings are stellar. I hope that a L6 expert views the info and some of the feature requests make it to the HD series.



Re: dual cab setlist/research
by meambobbo on 2012-10-01 07:59:29

I've had my dual cab stuff up for a few days now.  I'm just curious to know who all has tried it out, and what the general feedback is.

Please let me know if you tried the setlist I made and thought the tones were an improvement over the stock single cab/mic's.

Also, let me know if you tried to dial in other combinations of dual cabs using the spreadsheets, and if so you were able to achieve phase correction and thought it improved the tone.

Thanks, trying to slowly build support for this feature.



Re: dual cab setlist/research
by meambobbo on 2012-10-03 08:00:53

update - I have updated the setlist to include a delay or reverb or both on all the patches where I could - I know many people were concerned about not having enough DSP to add such effects.  Well they're in there now.  The end of the patch name indicates which they have (dr means delay and reverb, d just delay, r just reverb).

The individual patches are available here:

http://foobazaar.com/podhd/patches/dualCabs/

I">http://foobazaar.com/podhd/patches/dualCabs/">http://foobazaar.com/podhd/patches/dualCabs/

Idid not test the bean and pro versions, but I have Input 2 set to Mic per patch (for Bean compatibility).  A few patches use the FX Loop, so they won't work on the Bean, but otherwise, they SHOULD work.



Re: dual cab setlist/research
by tdollaway on 2012-10-06 08:34:31

I finally got a chance to try out the "dual cab setlist" last night. Great work, man! I really like te R-_X4 combo!

I'm usually one to use single amps, so I still have effects available. However, after trying it out last night, it's time to break out the trusty Boss and MXR stompboxes for any effects that I can't live without and use the POD mainly for my basic tone.  I really hope that Line 6 will listen to your suggestions as far as implementing both the "single amp/dual cab" configuration as well as the delay feature built into the mixer. It only makes too much sense.

Keep up the good fight, Meambobbo! I encourage anyone to do whatever they can to CONVINCE Line 6 to take notice!



Re: dual cab setlist/research
by meambobbo on 2012-10-11 06:50:19

i have added a section at the bottom of the original post detailing a couple ways this could be implemented.



Re: dual cab setlist/research
by Astaroth_CY on 2012-10-11 10:50:35

These tones are fantastic. I will probably start recreating all my tones using these as the backbone. BTW - doesn't the Vintage Pre have a phase adjustment parameter? Does that basically do what you need?



Re: dual cab setlist/research
by meambobbo on 2012-10-11 11:17:07

Phase adjustment on an audio signal can only occur by "flipping" the phase - basically turning crests into troughs and vice versa.  This is what the Vintage Mic Pre does, and I don't think it's useful here.  You'd basically just be inversing which frequencies were canceled and by how much others were out-of-phase.

Phase adjustment is more adjustible on a synthesized waveform, where you can basically specify the starting point of the wave.

When I say the two signals are out-of-phase, I think a better terminology would be out-of-sync.  Because of this latency in one signal, certain frequencies are out-of-phase, some so much that they are completely canceled.



Re: dual cab setlist/research
by meambobbo on 2012-10-11 11:26:12

To clarify, phase has to do with a specific frequency.  For 2 pure sine waves at equal frequencies, they can be in-phase (0 degrees), acheiving perfect constructive interference; or out-of-phase (180 degrees), achieving perfect destructive interferece or cancellation, or anywhere in between (0 degrees to 360 degrees).

For a given audio signal, it can be constituted as a hodgepodge of infinite sine waves of various frequencies and phases, and these vary over time.  So when two identical audio signals are out-of-sync and mixed together, some frequencies are in-phase, while some are out-of-phase, and which are in or out of phase will vary over every moment in time.



Re: dual cab setlist/research
by dahla on 2013-01-12 05:29:51

This is the most awesome thing I have discovered about the Pod HD. Your guide Meambobbo!

I have one question though; How do I convert the delay matrix to other sample rates? I still use 44.1, not 96...



Re: dual cab setlist/research
by Talenless on 2013-01-12 05:49:39

is there a way to convert these patches to work with the desktop POD HD model?



Re: dual cab setlist/research
by JimKidd on 2013-01-12 07:15:45

Bobbo, you are an artist



Re: dual cab setlist/research
by meambobbo on 2013-01-12 08:26:45

hmmm...i have not tested that at all.  there are two possibilities.

1) the Pod does all its processing in 96 kHZ then downsamples to 48 kHZ to send the SPDIF/USB signal.  In this case, nothing would change as far as using internal effects to delay one channel.  However, if you are exporting discrete left/right signals then adding latency via a plugin for your DAW, I assume you would need to set the samples to 1/2 the values stated.  a 48 kHZ sample occupies 2x as much time as a 96 kHZ sample, right?

I would bet if I had to that this is how it's done.  Setting the sample rate to 48 kHZ doesn't give you more DSP space, and it seems it would add additional complexity to the internal processing algorithms.  Downsampling at the end of the chain is far less complex...I think.

2) all the processing in the Pod is done at the sample rate selected.  this is a cluster #$%.  There's no guarantee any of my values hold if this is true.  Things may be 1/2, 1, or 2x...or they may adjust how things are processed, and the latency isn't as simple as a direct multiple of the values I found.  So I dunno.

I guess just try things out and let us know which way things sound best to you, in relation to exactly how you are applying latency.



Re: dual cab setlist/research
by meambobbo on 2013-01-12 08:30:49

i was in the process of doing that but got burned out.

i think i set input 2 to Mic rather than Variax.  So most patches, you should just be able to rename the extension from .h5e to .hbe and you can load them into HD Edit Desktop.  The exceptions are patches that use an FX Loop to add latency.  Since the bean has no loop, these patches won't work.  I believe the loop adds 40 samples of latency, so that'd be difficult to replace while leaving yourself enough DSP for ANY other effects.



Re: dual cab setlist/research
by meambobbo on 2013-01-12 08:32:06

And since I only provided a setlist file, you'll have to download HD Edit 500, open the setlist, drag and drop all the patches off to your desktop or another folder to get the individual .h5e files.

I KNOW...I'M SUCH A JERK.  8-p



Re: dual cab setlist/research
by meambobbo on 2013-01-12 08:32:20

not yet



Re: dual cab setlist/research
by dahla on 2013-01-12 10:46:05

Ah, I thought the pod used an internal SR of 48 kHz. I don't use the digital outs, so I guess if everything is 96 internally then the delay matrix should work regardless of the output sample rate. If the pod downsample at the last stage possible that is...

Man, this is technical...!



Re: dual cab setlist/research
by meambobbo on 2013-01-12 11:29:07

right...i'm pretty sure it uses a 96 kHZ internal engine, but I could be wrong.  If it does use 48 kHZ, then the signal should sound pretty much identical using digital out at 48 kHZ vs. 96 kHZ.  Which makes 96 kHZ kind of moot, other than using its clock as the master clock for your DAW.  I don't think that's the case, though.  I remember the X3 boasted using 96 kHZ vs the 48 kHZ on the XT, and I remember a significant sonic improvement moving to the X3, and I was only using analog outputs back then.



Re: dual cab setlist/research
by dahla on 2013-01-12 12:13:04

I searched the POD HD Pro v2.1 manual and found this:

Sample Rate Converter Active:

You’ll see this indicator light up whenever the device is operating at a sample rate other than its native 48kHz rate. In addition to 48kHz, POD HD Pro supports 44.1kHz, 88.2kHz and 96kHz rates by utilizing an internal sample rate converter. Please check your specific software’s documentation for details on configuring its audio sample rate.

It's for setting the sample rate when using the POD HDs interface capability... So setting the sample rate on the POD just means that your setting the output sample rate, meaning that it samples at 48 kHz at default internally, but can upsample or downsample at the last stage when using digital connections?



Re: dual cab setlist/research
by meambobbo on 2013-01-12 13:49:43

good find.  i guess the processing is all at 48 kHZ.  So technially all my values measured in samples should be halved, but it'll amount to the same thing, so long as you use the pod's effects to sync the channels.  if you use a DAW plugin to do it, then my values are all in 96 kHZ and must be adjusted if you use a different sample rate.  but they should be consistent with whatever rate you choose.



Re: dual cab setlist/research
by meambobbo on 2013-04-17 20:58:49

I redid the spreadsheet:

https://docs.google.com/spreadsheet/ccc?key=0AsSFadRSa9zYdG1kc1J2b1ZvRFVlUVIydXRMVVoyZnc&usp=sharing

http://foobazaar.com/podhd/toneGuide/CabsDelayTimes_V3.xlsx

Changes">http://foobazaar.com/podhd/toneGuide/CabsDelayTimes_V3.xlsx">http://foobazaar.com/podhd/toneGuide/CabsDelayTimes_V3.xlsx

Changesare:

1) I used a new methodology to find the values and has already proved to be more accurate

2) I color-coded the cabs for easier ability to find each cab combination matrix

3) I color-coded the cells that are best for easily dialing in a dual tone cab - greens require no additional effects for phase correction and blues require 1 EQ.

4) All the excel files are condensed into 1 using multiple tabs

5) the "Notes" tab contains all the instructions you'd need to utilize this data.




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