G
ggunn
Crystal Flavolian
At what cutoff frequency?
Getting rid of that brittle under-bridge pick up sound on amplified acoustic guitars.
pohaku
New member
I use a Sunrise in my B-25. It has its own sound, of course, but it is such a commonly used pickup that most people are quite used to that sound. In any event, I like it. No Quack. A used Sunrise is pretty affordable.
O
ofajen
Daddy-O Daddy-O Baby
I typically like to have the cutoff slightly below the fundamental of the lowest note. That way it's 6 dB/octave pretty much all the way up. The values I quoted are designed for guitar in standard tuning with a low E and produce a cutoff = 1/(2*pi*R*C) of 72 Hz. That's a tad below the fundamental of the open E string, but that's OK, since the full slope doesn't develop until somewhat above the cutoff frequency. You could step up to the next value of cap and that would lower the cutoff, probably to about 50 Hz, which is also an OK choice for guitar.
Going lower mainly serves to reduce level and require more makeup gain. However, it also extends the sensitivity compensation down into range below the lowest fundamental. It's up to you whether that's a good thing. On bass, I've used as low as 16 Hz and it works fine. 32 Hz works fine, too, and requires 6 dB less makeup gain.
The convenient way to tinker is to use a potentiometer, rather than a fixed resistor. At full value you have the lowest cutoff. By reducing the resistance across the pot, you raise the frequency until at zero resistance you have raised the cutoff all the way up and have no filtering. I believe this is the way Alembic tone controls work.
By the way, this question inspired me to play my Ovation a bunch last night. I lied... it sounds WAY better through the filter. Better than I remembered. Really no brittleness at all. That is with the "pre-EQ" setting turned off, just the plain pickup signal. Very natural on fingerstyle. I actually have to tone the bass end down a tad when playing with a pick, but it sounds very good in the upper register. In fact, it's a tone that works great for recording on its own. I'm sure it would also sound good in support of the acoustic tone.
Cheers,
Otto
G
ggunn
Crystal Flavolian
With the cutoff frequency below the fundamental of the lowest note, it would attenuate the entire range of the instrument at 6 dB/octave. If the cutoff freq were set at the lowest E, then the fundamental of an E at the 12th fret on the first string would be down 18dB. Is that what you are going for? It's hard for me to believe that such a thing would sound good.
O
ofajen
Daddy-O Daddy-O Baby
Yes, you have done the math correctly. There's really only one way to know for sure what it sounds like, and it's up to you to decide if it sounds good!
I use this type of system every time I play and it sounds great to me.There is a basic element of the physics of magnetic guitar pickups that explains why this works so well on electric bass and guitar with magnetic pickups: they use inductively-coupled pickups with a sensitivity that rises at 6 dB/octave, just like the repro (playback) head on a magnetic tape recorder (where the tape playback eq circuit has just this kind of 6 dB/octave integrating filter to compensate). I usually mix in a little of the original, unfiltered tone on a mag pickup, because the electrical properties of the pickup and cable already roll the high end off over the resonance, which is typically somewhere around 5K.
As far as these piezo pickups are concerned, I'm still studying the (less-familiar) physics of that, so I'm not yet sure what it is about them that causes that brittle sound. All I know is that when I use the same filtering I use on mag pickups, I get a good sound. There must not be any high end roll off on the piezo (it does have a built-in preamp, which helps), because all I need is the filtered tone. No need to add in a touch of the unfiltered tone to hold up the high end the way I do with mag pickups.
Have fun with it!
Cheers,
Otto
muttley600
Banned
Yes, you have done the math correctly. There's really only one way to know for sure what it sounds like, and it's up to you to decide if it sounds good!
There is a basic element of the physics of magnetic guitar pickups that explains why this works so well on electric bass and guitar with magnetic pickups: they use inductively-coupled pickups with a sensitivity that rises at 6 dB/octave, just like the repro (playback) head on a magnetic tape recorder (where the tape playback eq circuit has just this kind of 6 dB/octave integrating filter to compensate). I usually mix in a little of the original, unfiltered tone on a mag pickup, because the electrical properties of the pickup and cable already roll the high end off over the resonance, which is typically somewhere around 5K.
As far as these piezo pickups are concerned, I'm still studying the (less-familiar) physics of that, so I'm not yet sure what it is about them that causes that brittle sound. All I know is that when I use the same filtering I use on mag pickups, I get a good sound. There must not be any high end roll off on the piezo (it does have a built-in preamp, which helps), because all I need is the filtered tone. No need to add in a touch of the unfiltered tone to hold up the high end the way I do with mag pickups.
Have fun with it!
Cheers,
Otto
It has to do with the material properties of the piezo element itself. Specifically how they report the attack and decay at specific amplitudes of vibration and the way in which different higher partials are either accentuated or cut off at those amplitudes.
None of this has anything directly to do with resonance which of and in itself is meaningless. Can you explain what you mean when you use the term?
O
ofajen
Daddy-O Daddy-O Baby
Well, my discussion about magnetic pickups was just an explanation of why I built and use this filtering system, and the term "resonance" is relevant and quite meaningful in that case.
In a magnetic pickup, the turns of wire in proximity to each other have an equivalent self-capacitance which, when added to any cable capacitance present, resonates with the inductance of the winding. The more turns of wire in the winding, the higher the output voltage but the lower this resonance frequency. The load includes the resistance of the volume and tone control in the instrument plus any resistance to ground at the amplifier input and the capacitance between the hot lead and shield in the guitar cable. The cable capacitance has a big effect. These passive components form a resistively-damped second-order low-pass filter.
Does that clear it up?
As I said, I just tried it out on the piezo pickup and it sounds great. I don't know what the physics would indicate is an optimal compensating system for the piezos. I just know that this works really well.
It is pretty close to optimal when using magnetic pickups, at least up to the resonance frequency, and then you have to decide what behavior you want above that. I tend to just mix in the straight tone at a lower level (remember, it's rolling off at 6 dB/octave up to that point, so you've lost a fair amount of signal intensity up at 5K in the filtered tone relative to the unfiltered tone) and keep the same tone I had before above resonance.
The resistively-damped filtering of the passive components rolls off at 12 dB/octave, which more than compensates for the 6 dB rise in sensitivity due to the inductive coupling, so the high end is already rolled off somewhat with a (passive) magnetic pickup system. No need to filter up there. The convenient way is just to mix in the straight signal. That way there is no need to even figure out what the resonance frequency is. You just mix the signal in to taste and move on.
Cheers,
Otto
Zaphod B
Raccoons-Be-Gone, Inc.
I'm puzzled, too. You'd be attenuating the entire range of the instrument's response, at 6dB/octave.
muttley600
Banned
No not really, I ask because it's one term that consistently gets used (incorrectly) by my students. They use it often without any clear understanding of what resonance actually means within the field of physics and specifically in musical acoustics. Other times it is used by some wishing to blind an argument when they don't have the faculty to construct a clear explanation.
I'm not accusing you of either by the way. At least not yet.
Resonance refers only to the ability of a material to vibrate or oscillate more freely at specific frequencies owing to it's physical properties...
Resonance is observed primarily in one of four models or systems. Mechanical, acoustic, optical and electrical. They all observe the same boundaries and relate to each other. Also with the absence of electro magnetic induction and resulting impedance in a piezo element transducer I fail to see how the physics applies here or am I missing something?
O
ofajen
Daddy-O Daddy-O Baby
Indeed, you will. 6dB/octave is a gradual filter, however. If you already like the brittle tone of your piezo pickup, you may not like the filtered tone. It does, however, sound much more like a real guitar to my ears when using the filter! Words will not decide the question. Only listening can. Try it! The great part is that it is so cheap and easy to try it out.
Once you have the filter built, you still have many options for tweaking things to your liking. You can mix in a bit of the unfiltered tone. You always have the option to tweak the eq up a bit on the high end, either on the guitar or amp. My onboard preamp has tone controls, and sometimes I will boost the highs just a tad when playing fingerstyle, but the overall tone seems much more natural through the filter. By comparison, the unfiltered tone sounds brittle and unlike the tone of the instrument.
Cheers,
Otto
O
ofajen
Daddy-O Daddy-O Baby
No not really, I ask because it's one term that consistently gets used (incorrectly) by my students. They use it often without any clear understanding of what resonance actually means within the field of physics and specifically in musical acoustics. Other times it is used by some wishing to blind an argument when they don't have the faculty to construct a clear explanation.
I'm not accusing you of either by the way. At least not yet.
Resonance refers only to the ability of a material to vibrate or oscillate more freely at specific frequencies owing to it's physical properties...
Resonance is observed primarily in one of four models or systems. Mechanical, acoustic, optical and electrical. They all observe the same boundaries and relate to each other. Also with the absence of electro magnetic induction and resulting impedance in a piezo element transducer I fail to see how the physics applies here or am I missing something?
I've now said, more than once, just in this thread, that I am not talking about the physics of piezo pickups. Here's a quote from my previous post:
"As I said, I just tried it out on the piezo pickup and it sounds great. I don't know what the physics would indicate is an optimal compensating system for the piezos. I just know that this works really well. "
I was just explaining why I started using this system on mag pickups, which IS based on fundamental principles of operation of magnetic pickups. That it also helps give me a better, more natural tone on the piezo is just a happy coincidence, as far as I know. I make no claims that it is optimal for piezos or based on basic principles of physics for piezo pickups, only that it sounds good.
If anyone wants to try it out, they can and if they have questions, I'll try to help. I was just trying to help out the OP with the problem he mentioned:
"I'm trying to find a way to lessen that "brittle" sound in live performance..."
and I happen to know that this filter answers that same concern in a way I happen to like.
Cheers,
Otto
muttley600
Banned
I wasn't questioning that you personally like the way the filter works on your guitar. I was asking you how resonance would be relevant in a piezo system and hoping you would explain how your model does anything other than duplicate the process already being undertaken by other components in your signal chain. What you describe just seems to me to be a very crude filter. One that in my "limited" experience as a guitar builder and acoustician would do little to enhance the brittle response of a piezo transducer. Forgive my curiosity.
Zaphod B
Raccoons-Be-Gone, Inc.
Actually, I hate the sound of piezo pickups - they are the most unnatural sounding things. (Reminds me of Douglas Adam's description of the Nutrimatics Drink Dispenser on the Heart of Gold - to paraphrase, when you asked it to make a cup of tea, it made a liquid that was almost, but not quite, entirely unlike tea.Indeed, you will. 6dB/octave is a gradual filter, however. If you already like the brittle tone of your piezo pickup, you may not like the filtered tone. It does, however, sound much more like a real guitar to my ears when using the filter! Words will not decide the question. Only listening can. Try it! The great part is that it is so cheap and easy to try it out.
) Hell, maybe a 6dB low pass is what they need to make 'em sound decent. I just avoid them entirely.
O
ofajen
Daddy-O Daddy-O Baby
I wasn't questioning that you personally like the way the filter works on your guitar. I was asking you how resonance would be relevant in a piezo system and hoping you would explain how your model does anything other than duplicate the process already being undertaken by other components in your signal chain. What you describe just seems to me to be a very crude filter. One that in my "limited" experience as a guitar builder and acoustician would do little to enhance the brittle response of a piezo transducer. Forgive my curiosity.
Here are the two separate paragraphs where I distinguish the magnetic and piezo cases:
"There is a basic element of the physics of magnetic guitar pickups that explains why this works so well on electric bass and guitar with magnetic pickups: they use inductively-coupled pickups with a sensitivity that rises at 6 dB/octave, just like the repro (playback) head on a magnetic tape recorder (where the tape playback eq circuit has just this kind of 6 dB/octave integrating filter to compensate). I usually mix in a little of the original, unfiltered tone on a mag pickup, because the electrical properties of the pickup and cable already roll the high end off over the resonance, which is typically somewhere around 5K.
As far as these piezo pickups are concerned, I'm still studying the (less-familiar) physics of that, so I'm not yet sure what it is about them that causes that brittle sound. All I know is that when I use the same filtering I use on mag pickups, I get a good sound. There must not be any high end roll off on the piezo (it does have a built-in preamp, which helps), because all I need is the filtered tone. No need to add in a touch of the unfiltered tone to hold up the high end the way I do with mag pickups."
At no time did I suggest resonance was in any way relevant to piezo pickups. In fact, I implied the opposite by noting that there seems to be no high end roll off of the kind observed in magnetic pickups.
I discussed the situation with magnetic pickups mainly just to show where that filter came from and partly because some people who read this forum play basses and guitars with magnetic pickups, where that concept is very relevant.
Apparently, putting both subjects in one thread was a mistake.
I happened to discuss resonance in the context of magnetic pickups because it affects how I set up the filter and mix with the straight signal in that case. I contrasted that with the piezo case, where no such resonance and filtering seems to occur and thus the simple first-order filter seems to sound fine on its own.
Sometimes we mistake simple and elegant for crude. When it comes to magnetic pickups, the first order filter is simple, elegant and precisely what the physics calls for. It also happens to be what Alembic uses for a tone control in their $30,000 electric basses. They don't tell you it's to correct for the 6 dB/octave sensitivity rise that is an innate characteristic of all inductively-coupled magnetic pickups, they tell you that it is what they find sounds most natural based on their observations.
That same first-order filter is also precisely the compensating circuit used in tape recorder playback eq circuits to compensate the same 6 dB/octave rise in sensitivity we get from inductively coupled playback heads. It's similar physics and math in both cases. It's even the same in that we need to shut down the integration at some point in both cases: in the case of tape, we use eq curves (NAB, IEC, AES) that specify that we start to cut the flux at constant input signal sensitivity at 6 dB/octave above some specified frequency, basically to preserve adequate high frequency headroom, and thus the integration must stop at that same point to preserve overall flat response. In the case of a magnetic pickup, the overall system produces a second-order low pass filtering effect above the resonance, and so there is really no need to continue to filter above the resonance. The simple way to deal with it is to merely mix the straight tone in and let it dominate above the resonance frequency.
I will readily concede that using this thing on a piezo pickup is totally ad hoc. However, it is simple, easy and cheap and definitely an improvement over doing nothing, and thus should help the OP with his problem.
Cheers,
Otto
O
ofajen
Daddy-O Daddy-O Baby
Actually, I hate the sound of piezo pickups - they are the most unnatural sounding things. (Reminds me of Douglas Adam's description of the Nutrimatics Drink Dispenser on the Heart of Gold - to paraphrase, when you asked it to make a cup of tea, it made a liquid that was almost, but not quite, entirely unlike tea.
Hell, maybe a 6dB low pass is what they need to make 'em sound decent. I just avoid them entirely.
Hmmm, I take your point. If you're wanting tea, I don't suppose it matters if what you get is entirely unlike tea or almost, but not quite entirely unlike tea. It still isn't the taste of dead leaves in water. With milk. Squirted out a cow.
Well, I really haven't used my piezos much either. The Ovation has a good tone, so I just mike it. I never really liked the piezo tone much. But, then, it can be handy to plug in and use that in a live situation. That's what the OP wants to do. Still, the bare tone is not very good. This filter does help. It still lacks some of the substance of a real guitar tone, but the overall balance and character is better.
Cheers,
Otto
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DrewPeterson7
Sage of the Order
Actually, I hate the sound of piezo pickups - they are the most unnatural sounding things. (Reminds me of Douglas Adam's description of the Nutrimatics Drink Dispenser on the Heart of Gold - to paraphrase, when you asked it to make a cup of tea, it made a liquid that was almost, but not quite, entirely unlike tea.
Hell, maybe a 6dB low pass is what they need to make 'em sound decent. I just avoid them entirely.
I love that line.
The one caveat I'll add, is while they sound almost, but not quite, entirely unlike an acoustic guitar, sometimes that sound actually works very well for a part. "direct" sounding acoustics can sometimes sound pretty cool mixed way back behind something else, and I've always kind of dug the sound for single note lines with a kind of "exotic" flavor to them, where the fact it doesn't really sound that like a guitar is actually a boon.
I like having a piezo in my acoustic for two reasons - one, it's nice to have the timbral option even if I almost never want to use it, and two (and probably more importantly
) it's VERY rare to find acoustics with cutaways and no electronics.
Zaphod B
Raccoons-Be-Gone, Inc.
Oh, for sure. Just like any other sound, it is what it is and in the end it's just another tool in the toolbox. I have a hell of a time getting my Martin to mic up for a mix because it's so boomy, so I can't exactly pontificate on the superiority of a purely acoustic sound.I love that line.
The one caveat I'll add, is while they sound almost, but not quite, entirely unlike an acoustic guitar, sometimes that sound actually works very well for a part.