#1
I have an Ibanez acoustic electric and it has a knob labeled Notch frequency and a Phase button. can anyone explain what those two things really do?

Thanks.
#2
Notch is to filter out a certain frequency. You would use it to cut out feedback. The phaseis also used to filter feedback. I forget exactly what it does but when you plug in to an amp play a low E and if you are getting feedback adjust the notch filter. If you can't get rid of it, click the phase button and then redo the notch filter.
#3
The guitar has an internal resonance called a helmholtz resonance. The this resonance is a slightly different frequency from one guitar to the next. When an amplified note is played that is the same frequency as the guitar’s helmholtz frequency it is often times much louder than the other notes on the guitar so often people use the notch filter to zero in on this frequency and reduce it. Because the guitar will resonate the helmhotz frequency in sympathy with any note played it is easy to get a feedback loop. So the notch filter can help stop this type of feedback as well as balance out tone.

When you pluck a note on your guitar the vibration is detected by your pickup which is run to your amp and then played back much louder. If you turn your amp up too loud then the vibration from your amp is sensed by your pickup and fed through to your amp again. This process is what results in feedback. The phase button inverts the soundwave. That means that a wave would go from something like this /\/\/\/\ to this \/\/\/\/ They sound exactly the same but because they mirror each other they don’t loop and cause feedback. Unfortunately the phase button doesn’t always usefully kill feedback loops because the shape of the room and speaker placement can change the phase of the sound waves too.
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#5
CorduroyEW I wish I had your thorough explanation before I got rig of my last acoustic. The high E seemed to sound three times louder than the rest. And the dids at Guitar Center were no help. The electronics had "Notch" on the interface but I hadn't a clue that I could have used that to simmer that E down to a boil.
#6
CorduroyEW understands the physics of sound. Very precise explanation of a guitar's resonant frequency and notch filter application.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
#7
Quote by RareBird0
CorduroyEW I wish I had your thorough explanation before I got rig of my last acoustic. The high E seemed to sound three times louder than the rest. And the dids at Guitar Center were no help. The electronics had "Notch" on the interface but I hadn't a clue that I could have used that to simmer that E down to a boil.
I don't think a "notch filter", would have done anything to help you anyway. Those types of filters are "high pass", and only modify frequencies BELOW, about 300Hz.

The high e-1's fundamental frequency is well above 300Hz, thus it doesn't enter into the realm of "Helmholtz resonance", at all.

You would have used the high frequency controls of a multi-band equalizer to have any chance of taming that. As you likely know, that's what the adjustable pole pieces on electric guitar pickups are desined to combat.
#9
Quote by Tony Done
....[ ]....Also Helmoltz refers to the air resonance frequency, which is only one of the resonant frequencies in a guitar.
Right but, Helmholtz resonance is directly linked to chamber volume. Thus, an LF "notch filter" only addresses itself to that specific issue, which is, well below e-1.

I have a 12 string with a B-Band onboard preamp. That has an extra, "presence" (*) slider, which would be more likely to effect HF issues.

(*) This in addition to the normal low, mid, and high controls.

I don't know if this has been covered yet but, I think you can use the phase swap to cure issues with phase cancellation between the guitar and an amp also. One position should give you slightly better bottom end if you're in proximity to the amp... (Don't quote me on that though. it's sort of a hunch).
#10
A phase switch is often used when there is more than one pickup in an acoustic guitar, and it switches the phase between the two pickups. I installed one in one of my guitars between the piezo and magnetic pickups. Surprising to me, it doesn't have much effect on tone, but it is supposed to be one method that can be used to peliminate feedback at specific frequencies. I don't know how else it is used, but I can see that such a switch could be used between pickup and amp.

The Maton AP5 preamp has a nice arrangement. High and low sliders, plus two knobs, one that controls midrange peak and the other for cut-to-boost. The mdrange control gives a good range of tones, especially noticeable when strumming. Your "presence" control is probably in the 5KHz range, well out of the feedback area.

Just remembered. The Baggs Mixpro, a universal preamp-mixer, had a phase switch between the two pickup inputs. I used it for combining magnetic and piezo, though it also had phantom power capability for a microphone.
#11
I really hate this new post box arrangement. It won't expand, thus you have to keep scrolling up and down through your post to figure out where stuff is. That said
Quote by Tony Done
A phase switch is often used when there is more than one pickup in an acoustic guitar, and it switches the phase between the two pickups. I installed one in one of my guitars between the piezo and magnetic pickups. Surprising to me, it doesn't have much effect on tone, but it is supposed to be one method that can be used to eliminate feedback at specific frequencies.
Yes, as do two out of three of my Crafter 12 strings. Actually when you put two pickups out of phase, the LF notes cancel one another out, hence eliminating some of the feedback potential. This is something which ties into home stereo speaker setup. In phase, the two cones move in and out together in sync with the signal. If the two speakers are "out of phase", the two cones travel in opposite directions to the same signal, and effectively suck the bass out of each other. In a laboratory controlled environment, total silence can be produced at the exact midpoint between two out of phase transducers. A bit more difficult to pull off, is creating total darkness between two out of phase light sources, but it is still theoretically possible

Quote by Tony Done
I don't know how else it is used, but I can see that such a switch could be used between pickup and amp.
Well, even in low gain situations there is an audible difference between in phase and out of phase pickups. Granted though, it is fairly subtle. Some of the bass is cancelled, and the system begins to take on a "honky" sound in the midrange . However, in a very high gain distortion situation, out of phase pickups produce a very audible, bizarre harmonic "squawk". Many bands use the effect, although I think one of the guitarists in "Lynyrd Skynyrd" tended to use it in abundance. The guitar's bass is also somewhat killed when you mis- phase the pickups. I think many electric guitars come with a phasing switch. The feature usually would be offered either with, or after, the coil split option for humbuckers. Out of phase pickups are one of those things, you'll know it when you hear it, but only after someone tells you what it is.

Quote by Tony Done
The Maton AP5 preamp has a nice arrangement. High and low sliders, plus two knobs, one that controls midrange peak and the other for cut-to-boost. The mdrange control gives a good range of tones, especially noticeable when strumming. Your "presence" control is probably in the 5KHz range, well out of the feedback area.
Indeed it is. I think the range it controls is somewhere between 2K & 5K Hz. While the e-1's frequency certainly isn't that high, its upper harmonics can extend into that range, and a presence control will "take the edge of", a particularly spitty high end. That's why I offered that as a suggestion for the "too hot e-1", rather than the mid sweep, which may or may not, go high enough to make a difference. Cutting the presence a bit, would also tame some of that mythical "piezo quack".

Anyhow, Ibanez' "Shape Shifter Preamp" is quite a nice device. It has that contour control & phase switch, but it also runs on just two AA batteries! (3 volts instead of those damned expensive 9 volt PiTAs). Ibanez acoustics tend to sound very good plugged in. Unplugged, you ask? That's quite a different story.

So we're clear here for perhaps for our less experienced electronically newer members, when pickups are "out of phase", one is generating a positive electrical signal, while the other is generating a negative signal. "In phase", they both go positive or negative, together, in sync.
#12
Quote by Captaincranky

So we're clear here for perhaps for our less experienced electronically newer members, when pickups are "out of phase", one is generating a positive electrical signal, while the other is generating a negative signal. "In phase", they both go positive or negative, together, in sync.


Yes, and the effect is very noticeable with two magnetic pickups, say bridge and middle, not so much when different kinds of pickups as being used, as in a magnetic and a piezo.