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[NOT A BUG] Axe-Fx II - VU meter issue (1 to 2dB low after preset recall)

Alex C

I'm currently on Quantum 2.00.

A week or two ago I had leveled my presets with the VU meter and then slightly by ear, and everything was good, as it had been the dozens of times I had leveled in the past.

Today I checked the VU meter on one of my main presets and saw that it was between -2 to -2.5dB, even though I had last leveled with 0dB as my target (with this same guitar and pickup and volume knob setting). I scanned through about 20 of my main presets and found a similar situation on all of them. I never adjusted global input level or anything like that, and although I couldn't explain why this was the case, I went through and re-leveled these 20 main presets to ~0dB.
After this I returned to the first preset I had leveled, and found that it was centered somewhere around -1.3 as I strummed. Even when I dug into the string, it didn't get higher than -1dB. I found a similar situation on the other presets that I had just leveled.

To eliminate the variable of string strumming strength, I saved the preset to a new location and added a synth block with a sine wave in front of the amp. I re-leveled to about 0dB (the meter varied by about +/- 0.4dB), saved, navigated to an adjacent preset and then back, and the VU meter now showed a reading with a center at about -1dB.

Below is a gif showing this behavior (sorry for the low quality; I wanted to keep the filesize down):

This was with the Two Stone amp model, but I tested it with a Supertweed and others, and it happens with those as well.


Some other variables that affect the VU meter reading: how fast you strum, which strings you hit, and how evenly you hit those strings.

Depending on how you've set up the amp (gain, etc.), steady strumming will produce one reading, but if you let the strings ring out, the level will climb upward and then drop off. A relatively small difference in how fast you strum can make a significant difference in how the meters read.

Alex C

Some other variables that affect the VU meter reading: how fast you strum, which strings you hit, and how evenly you hit those strings.

Depending on how you've set up the amp (gain, etc.), steady strumming will produce one reading, but if you let the strings ring out, the level will climb upward and then drop off. A relatively small difference in how fast you strum can make a significant difference in how the meters read.
Thanks for the reply. I've noticed this in the past, and when I level presets I try to strum the lowest four strings repeatedly and with the same intensity to keep things consistent.

In this case, since I thought there might be a separate issue, I took string strumming out of the equation by using a synth block with a sine wave as the input signal to the amp. (I did mention this in my previous post, but maybe I got too wordy.)

So I level the preset at ~0dB using a sine wave, save (and check the VU again to confirm 0dB), change presets, change back, and it's now at ~ -1dB.


Sorry, I missed the synth. That explains why your levels are so steady. I've never seen them that constant before.

I don't have an answer for you about the 1 dB difference, but I do have some ideas on how you can get more consistent results.

First, ditch the synth. Its signal is nothing like the signal coming from your guitar, and the levels coming out of your amp won't be typical of the signals you'll get while you're playing your guitar.

Instead, strum steadily—maybe two or three times a second. You'll see the VU meter jump around more, but the results you get will be closer to the real-world levels you'll get while playing.

Strum all the strings, not just the bottom four. They all contribute to your level. When you just strum the bottom four, you're leveling the bass part of your tone, not the whole thing.

And don't forget: the VU meters can only get you into the ballpark. How loud a guitar tone sounds is affected by the gain structure in the amp model, the effects you're using and how you dialed them in, how hard or soft you and the band are playing...lots of stuff beyond what a meter can tell you. You have to do your final tweaks by ear, with the band behind you. If the meters get you within 1 dB, that's about the best you can hope for.

Alex C

Thanks for replying again. The tip about strumming all of the strings when leveling is a good one. Other than that, though, I think we're on the same page on everything. I've always used the VU meter as a starting point, followed by a final round of tweaking by ear. I strum the open strings quickly and consistently (like the strumming pattern on Santo and Johnny's "Sleep Walk").

This has always worked well for me, but in this case I was surprised to see different VU meter readings when returning to a preset I had just leveled near 0dB. I only used the synth block to remove the guitar (pickup, volume setting, strumming strength and technique, bad cable, intermittent connection, etc.) from the equation while I explored a possible bug. I'm not expecting extreme precision from the VU meter; I just expected consistent results when the source is a fixed frequency and amplitude.

As an update, I turned on the Axe-Fx briefly this morning, but this issue was not apparent during my brief testing before leaving for work. I tested this again with white noise, and it functioned as expected, returning to ~0dB after saving, navigating away, and recalling. So did pink noise, and then so did the sine wave when I tested with that again. I'm not sure what the issue was, but it wasn't showing up this morning. I'll test some more tonight.

Alex C

Another update: I checked this out again last night, and the issue is still occurring on most presets. (All of my presets have the same "template," with only the amp and cab models being different in each.)

The following situation occurrs on multiple presets.

1) Bring up preset and strum. VU meter reads ~ -1.5dB, Amp Level reads ~ -3.5dB
2) Increase Amp Level until VU meter reads ~0dB. Amp Level now reads ~ -2dB
3) Save preset, confirm VU and Amp Level readings
4) Navigate to an adjacent preset, then navigate back (I tested this using the front panel knob as well as the MFC, and also tested with the MFC unplugged)
5) Check VU meter. It now reads ~ -1 to -1.5dB. Amp Level is at the updated value, -2dB.
6) Repeat steps 2-4
7) Check VU meter. Again it reads ~-1dB. Amp Level is now -1dB or -0.5dB
8) Keep repeating this process until Amp Level is +5dB or more, and upon preset recall the VU meter still reads -1dB or lower


Can you post one of these presets?

Two versions of one preset would be ideal, before and after the process you described. It would also be good to verify that importing both versions from computer reveals the issue.
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Alex C

I had some more time to investigate this. It seems like I was wrong when I reported that it was still happening with the MFC unplugged; I had three minutes before work that morning to try out a few scenarios, and I must have gone too quickly.

I use "Matman's Global Volume Boost Trick" on the MFC, so at first I thought that might be causing this problem somehow.
Then I remembered that I have two external switches connected to the MFC that I had used at one time for volume increment and decrement (before the VU meters came along and made it much easier to get in the ballpark).
Unplugging this set of switches fixed the issue.

The switches are stompbox latching foot switches, but they must not have been set up correctly in the MFC, because it takes two stomps on a switch for an increment/decrement to occur. (I might have done this intentionally long ago, thinking that this would avoid accidental volume adjustments.) The decrement switch must have been pressed recently, and it was sending a MIDI command upon preset recall, so every time the preset was loaded it was reducing volume and saving immediately. I examined my main presets that had been leveled multiple times, and on many of them the output block's main level was between -15 and -20. This explains why I was able to keep cranking up the amp level more with each save, and the VU meter was still reading low. I guess it was happening to each preset as I simply scrolled through, which is why so many were affected and why some were so low.
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