What's Up with the Mesa Walkabout Mid Knob?

IIRC, the mid knob is cut only just like on those classic Fender tone stacks, so 'flat' would be fully CW.

And, you have to admit, it does sound great.

Well, the new Villex system works some kind of cut/boost magic while remaining passive. Maybe it's something similar?

Jeff Scott said:

IIRC, the mid knob is cut only just like on those classic Fender tone stacks, so 'flat' would be fully CW.

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Straight from the M-Pulse 360 manual:

"Unlike the BASS, this control is boost only,, and while it can competently remove this broad spectrum of midrange from the mix, it cannot provide the extreme attenuation of an active style control. . . . It is hard to dial wrong with this more forgiving control as it seems to give you just enough and no more. This simplicity can be a welcome respite from the higher tech power of the adjacent tone controls . . not to mention the 5 Band Parametric."

Count me as being confused as well. If it is boost only, how can it "competently remove" midrange? I'm no expert, but that doesn't make sense to me. Also, if it's passive, doesn't that seem to suggest what Jeff Scott is saying?

Just for kicks, I am going to record some bass tracks with the MID knob on different settings (and everything else flat) and then analyze the frequency spectrum of the different tracks to see what it does. I will post my findings in this thread.

The mid control IS fully passive, and only cuts mids.
Think of it exactly like a tone knob on a Jazz or Precision passive bass.
All the way open (fully clockwise) is flat - turning counterclockwise cuts mids, just the way it cuts highs on a Fender bass - the way you'd get a Motown sound on a P bass.
This is explained well in the manual and was also explained in the Walkabout Scout review in the BP Jan '04 issue.

BTW - A walkabout is NOT an M-Pulse 360, and has little to do with it and more to do with the M-Pulse line.
Comparing one to another is apples & oranges comparison.

cmhgreg said:

Just for kicks, I am going to record some bass tracks with the MID knob on different settings (and everything else flat) and then analyze the frequency spectrum of the different tracks to see what it does. I will post my findings in this thread.

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That would be great if you could do this I'd be interested to know where flat is exactly.

one thing that I could think explains it is if there is a fixed gain stage after the tone control that compensates for the cut of the passive tone. So while it's fully rolled off and cut it's frequency range as much as possible the gain stage boosts it to flat. Then as you turn the knob it appears to boost the signal even though it's just the passive mid decreasing the attenuation amount.
So while the mid might be passive there could be something that boosts it by a set amount of decibels afterwards.

To me the only way a passive mid could be boost only is with something amplifying it after. Although it doesn't explain how it can "remove a broad spectrum of mid range for the mix"

Well, my quick little test seems to prove that it is not a misprint and that, in fact, fully counter-clockwise is flat.

Here is what I did. I recorded straight from the DI on the M-Pulse 360 into a Presonus Firestudio Project. The parametric EQ and compressor settings were set to off. First I recorded tracks with the DI switch to pre so that the signal bypassed the preamp. I recorded successive open strings and let the notes ring. Then I set the DI switch to post, set the bass and treble to flat, and repeated the procedure, first with the MID knob all the way counterclockwise, then at 9 o'clcok, 12 o'clock, 3 o'clock and fully clockwise.

I then opened the wave files in Adobe Audition. Using the Frequency Analyzer, I took various snapshots of the wave forms and compared them. I am completely confident in saying this: when the MID knob is completely counter-clockwise, it is flat. There is no question in my mind after analyzing the frequencies. The snapshots I took of the "pre" sample and the snapshot I took of the "post" sample with the MID knob fully counter-clockwise (and everything else flat) were virtually identical. When the MID knob is rotated clock-wise there is noticeable boost being added in the mids. Just like the manual says, it is boost only.

Our ears can play tricks on us, but seeing is believing.

cmhgreg said:

Our ears can play tricks on us, but seeing is believing.

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+1

As I suspected.

Any chance you could post the pics of the frequency analysis?

Passive boost, eh? Pretty interesting!

theshadow2001 said:

Although it doesn't explain how it can "remove a broad spectrum of mid range for the mix"

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I'm still confused about that. The only way you could cut mids would be to have the MID knob flat, boost the bass and the treble knob and then reduce the master volume to compensate for the boosts. I don't know if maybe that part is a misprint, but I think that is the language in the manual that causes all the confusion.

cmhgreg said:

I'm still confused about that. The only way you could cut mids would be to have the MID knob flat, boost the bass and the treble knob and then reduce the master volume to compensate for the boosts. I don't know if maybe that part is a misprint, but I think that is the language in the manual that causes all the confusion.

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well that's what I was thinking as well. Although then it wouldn't really have anything to do with the mid control would it. It would be the Q of the bass and treble controls that determine how much mid is "cut"

It's mostly just a really poor effort on mesa's behalf in terms of writing the manual and proof reading it and not following it up when customers said they were confused.

Edit: Actually I think that deserves one of these ---->

Not sure how this is going to come out, but here is a screen shot from my test. This particular snapshot is of an open A string. The green outline is the "pre" track. The red outline is the "post" track with the MID knob fully counter-clockwise. The purple outline is the "post" track with the MID knob fully clockwise. The blue frequency data on the bottom is just the noise floor from an idle part of the track. I had to set the cursor at a place where there wasn't any signal so that the colored outlines that I froze would be more visible.

I have to agree. My ears tell me that fully CCW is flat and that it is a boost only circuit.

Rhythm5 said:

I have to agree. My ears tell me that fully CCW is flat and that it is a boost only circuit.

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This is how I hear that control also. There was some technical post quite a while ago about why Mesa calls it 'passive', even though it's really a boost only circuit (or seems to be anyway. I can't remember.

Whatever it is, I like it a lot, and that 9 o'clock to 12 o'clock range has a lot of nice tonal variation, from relatively clean, wide and somewhat modern, to growly, punchy tubey vintage tone... nice!

Perhaps M/B considers a mid control that is not semi-parametric "passive"? That would explain a lot, but it does put M/B in a bad light regarding their terminology. :scowl:

Jeff Scott said:

Perhaps M/B considers a mid control that is not semi-parametric "passive"? That would explain a lot, but it does put M/B in a bad light regarding their terminology. :scowl:

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I don't think that's the case. I wish I could remember the explanation. It had something to do with the general voicing of the amp being very mid-oriented, and the passive control reduced that... so that even though it seems like it's boosting, it's really kind of like a 'reverse' passive tone control... cutting the max when 'off'. That's not exactly correct, but it's something like that....

I tried to search but the post is buried somewhere and I can't find it.

Whatever it does, it's a cool control... massive tonal variation from 'off' to noon.

Page 10 of the Walkabout manual has factory sample settings.
#2 is labeled: "Scooped" R & B - this definately refers to scooped mids.
It has the passive mid control knob fully counter clockwise (to Left), as well as some cut in the 350 Hz region
on the mid band of the semi-parametric EQ.

This, IMO, implies that scooped (diminished) mids is when the mid control is fully CCW - therefore it can be taken that flat is fully CW.

On page 3 of the manual, under helpful hints - it says the mid control knob works like a normal passive control, and BOOSTS a broad band of frequencies as it is increased. This wording is what is confusing some of you - but it is simply a description of how your ears will perceive what this control does - it SOUNDS as if the mids are being boosted - but they are merely being re-introduced to the spectrum from the fully cut mids when the control is fully CCW.

Again - think of the tone control on a passive Fender bass - as you increase the control CW, it SOUNDS as if the treble is being boosted, but in reality, we all know that this is not true - fully CW is flat, and fully CCW is actually CUTTING this range. To my ears, on a Fender, a fully CW passive tone setting sounds as if the treble is boosted - but if you've ever played a Fender where the tone pot is eliminated from the circuit, the tone is the same as if the passive tone control is fully CW.

Doesn't this all make some sense ? It is not all that confusing.
But - I did not design the amp, and I could be wrong !!
If you have some confirmed better info on this - please share.
Has anyone called Mesa to get an explanation from a tech on this issue yet ?

KJung said:

I don't think that's the case. I wish I could remember the explanation. It had something to do with the general voicing of the amp being very mid-oriented, and the passive control reduced that... so that even though it seems like it's boosting, it's really kind of like a 'reverse' passive tone control... cutting the max when 'off'. That's not exactly correct, but it's something like that....

I tried to search but the post is buried somewhere and I can't find it.

Whatever it does, it's a cool control... massive tonal variation from 'off' to noon.

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http://www.talkbass.com/forum/showthread.php?t=206021&highlight=mesa+mid+control

This could be the thread you are refering to that I started some time ago (that I had forgotten about). I came to pretty much the same conclusion back then in a slightly more conveluted sense.

Bill Fitmaurice did a much better job clearing it up.