Iii. Phase Correction

You may notice a drop in high-end response and/or a dead or phasy tone when you first combine the cabs. The dual cab combination you chose is likely experiencing a comb filter. Anytime you record a single audio source with two mics that are at different distances, there will be negative interference occurring at regular intervals throughout the frequency spectrum. In short, this means the tone has dead spots. This is due to a slight delay in one of the signals. For certain frequencies, the two signals perfectly cancel out. Others are just out-of-phase to various degrees, while some perfectly reinforce each other.

Higher-pitched frequencies get the worst of it. Because they have a shorter wavelength, even a slight delay can cause perfect cancellation. This is probably what you notice. The tone sounds like a blanket was thrown over the amp. Even though the Pod is using different cabs, the signals aren't as different as they sound. Even the dark cab has some treble in there, and it can wash out the bright cab's high-end. Even if you use the same mic on both cabs, it doesn't mean the signal isn't delayed more in one than the other. This could be a result of how the cabs themselves behave, differences in the distances Line 6 used to mic them, or differences in how the DSP processing implements them.

I have discovered a method to phase correct the two cabs. Some effects can be set to be transparent to the signal; however, they do require processing time, which introduces a very slight delay to the signal. The most common effects I use are EQ's and Compressors. By using a combination of such effects, we can acheive phase correction. The difference is night and day.

Author's note: the information below gets fairly technical and might be more work than necessary. The easier way to do this is to simply throw a parametric EQ with default settings behind one of the amps before the mixer. Toggle it on/off and see if the tone improves with it on. If not, do the same test on Channel B. If the tone sounds muffled with no EQ, EQ on Channel A, and EQ on Channel B, or if it just sounds "off" and "phasy", give up on the combination you've picked - you'll probably need to use 2 or more effects to phase correct the cab/mic choices, which starts to become a hindrance. I list combinations below and in Appendix C, this spreadsheet/alternate Google Cloud version/pdf version BROKEN LINK that work well using 0 or 1 EQ's. This setlist BROKEN LINK CANNOT DL???also contains examples.

I have done some pretty thorough research on this, and am continuing to update it. The link below is a spreadsheet with a matrix of every possible combination of cab/mic with another, for the Tread V-30, Hiway, XXL, Greenbacks, Uber, Brit, and Blackbacks 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. It contains tabs on how to use it, a list of relatively tone-transparent effects with the amount of delay they introduce, and the combination of effects necessary to get any particular amount of delay.

Cab/Mic Delay Times Matrix/alternate Google Cloud version/pdf version

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 a delay of 10 samples in Channel B and 6 samples in Channel A, giving you a difference of 4 samples in Channel B. This is where the FX Combination Delay Times spreadsheet is useful - you can quickly look up combinations that will yield delay samples in increments of 1 sample from 1 to 20+.

I have color-coded the cells that require 0 or only 1 EQ effect. I recommend sticking to using these cab/mic combinations. Otherwise you risk having to use too many effects blocks or DSP on phase correction, or you have to use effects whose tone-neutrality is highly suspect.

If this seems confusing, it can be a bit tricky at first. That is why I made this setlist. BROKEN LINK CANNOT DL??? It contains numerous example patches demonstrating how to achieve phase correction. You can toggle the effects on/off (usually with FS2) to hear the difference they make to the tone.

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. Edit: I found the striked-out statement to make my sound too thin. With proper pairing of cabs/mics and dialing in of the low-end response on both, you should not need to kill the bass on your bright cab. The bass will remain rich and powerful.
• 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". Edit: I do tend to dial back the treble on my "dark cab", but rarely to 0%, this can leave the tone sounding like something's missing. I dial it up until it starts to sound like it's interfering with the bright cab's highs, than back off a touch. You want it to fill in some frequencies but not take too much focus away from the "bright cab". I usually end up with EQ settings within 15% of each other between amps.
• 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, or even a simple Parametric at 6 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. If you want to help out on this front, please see this thread. BROKEN LINK
• Don't write off an EQ used for phase correction as a dummy block that's being wasted. Use it however you can. I'll often use a Mid-Focus EQ to get my phase-correction latency on my bright cab, then use its low pass to roll-off the excessive high end. Or I might dial additional hot djenty presence frequencies with a Parametric EQ. Similarly, if my dark cab has a boomy punch or excessive warmth, I can dial out those frequencies with a parametric EQ.

The tone might be too trebly for your taste. Don't worry about that - we're going to EQ later. You want the tone that sounds the least filtered/phasy/dead and the most like a single amp tone. Sometimes increasing the delay between the cabs reduces the frequency cancellation in the high-end but adds more ambiance to the tone. I don't like this - I want to reduce the delay between the cabs to as close as I can get to 0. You can use E.R. and the Cab DEP Decay to add slight ambiance and thicken up the tone.

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iv. EQ'ing the tone

With two sets of amp EQ's and possible EQ effects on only one channel, EQ'ing can get much trickier than with a single amp tone. The important things to remember are that the controls will work slightly differently for each channel given the cabs' different frequency responses, and some frequencies will sound a bit better in one channel than the other. However, dialing frequencies out completely can make the tone "small" or a bit dead. I find both amp's need somewhat similar EQ settings, but not exactly the same. The ultimate goal is to blend them together for one full-range sound, playing into the strengths and weaknesses of each cab/mic.

For amps where you're using power amp distortion, EQ settings will affect distortion tone. In these cases, I want the EQ settings virtually identical...at least to start. Only after finishing the rest of my patch and using as many EQ effects as possible for final EQ will I revisit these controls to try to get the final EQ I want.

I also often like to put a Mid Focus EQ at the end of my chain. This helps me roll off some of the extreme highs and lows. You can also use the Gain parameter as a final patch volume, rather than having to change both Mixer Levels or the Amp Volume controls.

You'll probably still want further EQ treatment. I find a Parametric EQ or two behind the mixer (applied to the mixed signal) is usually enough. The phase-correction EQ's above can help as mentioned above, but they won't have as powerful of an effect as a post-mixer EQ. However, since DSP is tight, it's best to make smart choices for them to get as much as you can from them and your amp EQ before trying to add post-mixer EQ blocks. This is especially true for lead patches, where you need some time-effects, or patches that need pitch or mod effects.

Keep in mind that the Cab DEP's will also affect final EQ. Sometimes they can be slightly tweaked for EQ purposes without changing the tone too much. But more extreme changes will affect the tone. So primarily use them for that purpose.

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Date: 2016-01-03; view: 798