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Topic: How to TWO |
ed packard
From:
Show Low AZ
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Posted 6 Jul 2006 3:29 pm |
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In the opening post of the How To thread, two PSG related subjects were introduced for consideration re measurement methods and meaning.
One of these two was the Tension on a string for the desired pitch. There seemed to be two views on the equation given; one was that it was valid for the Scale Length, the other that it somehow included the Total String Length if it was correct. A measurement method was given in the opening post to prove or disprove the two viewpoints. We will leave that subject, and move on to the second subject presented there…That which is closely related to tone, attack, sustain, and pitch as a function of time after string excitation. To save the trouble of looking in the previous thread, here is the opening statement.
“Now about the tone/sustain/harmonic/bell/etc. thing...these, also can be measured. The units will be harmonic content vs. time, in one form or another. The equipment needed is available in many computer soft-wares for recording, but usually not with the appropriate controls and data processing capabilities.
With the appropriate computer program, the instrument harmonics (as provided from the pickup) can be captured and seen/analyzed. This method provides a way to see the amount of harmonics in a single string, to all strings at once, and as a function of their tension, where and how they are excited (picked/hammered), where the pickup is located, etc.. The basic program costs less than your volume pedal (pot type). The program provides a Frequency Spectrum Analyzer, and Oscilloscope in one package. It is used for acoustic design from speaker cabinets to room size/shape/material compensation.”
This prompted the following response from a Forum member, Joe Meditz.
“Ed's graphs are time frequency plots. The frequency response at a given time can be adjusted with an equalizer. However, since the shape of the freq response curve does not remain constant, the equalizer would have to change from the time of attack and throughout decay. This could be done on a digital signal processor. http://s75.photobucket.com/albums/i287/edpackard/?
The question for Ed is: Using your measurement data, do you think that one could make a box that you plug your steel into that will make it sound like JD's Emmons? Now that would be something!”
I had the audacity to answer yes, with qualifications.
Then, in another thread Eric West asked:
“Ed, I have a request when you have time.
Inre to two questions:
One. Is there a way you can represent a graph and timeline of the change in pitch on a plucked string over a say one second interval in hz and seconds? (Certainly sharp immediately because of the initial disturbance.)
Two. Vindictivity (sp).
When a string that has been at rest for a given time, say 12 hours is plucked hard, does it draw up for a certain period of time, in a very small incriment of a hz?
These are not trick questions, I just wondered if you have the equipment, and/or the time to put this into documented form.
Thanks for any answer”
It turned out that while I did not have an off the shelf solution, Joe Meditz came up with one, and sent Eric and I a copy of the results, and sent me an explanation of how he did it.
This all leads back to the session at Jim Palenscar’s steel shop last Dec. where we measured, photoed , and captured the sonic behavior of 32 PSGs. When we first talked about doing this, WAV recordings were discussed for the sonic properties. This was bypassed in the interest of time. After boiling down all the info gathered at the session, we are ready for the next session to go deeper into the differences et al.
The first session dealt with the signals and frequency spectrum for all open strings (from the pickup) excited by a thumb pick sweep at the 12th fret. The next session will deal with the output from each string under a variety of conditions, such as where and how picked, plus some bar location tests. The plan is to WAV record this data as well as to capture the FSA data as before.
We will try to get Joe Meditz to participate in the session so that we can tune the data gathering to his post processing methods. It is convenient that Joe lives in San Diego.
[This message was edited by ed packard on 07 July 2006 at 07:24 AM.] |
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Charlie McDonald
From:
out of the blue
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Posted 7 Jul 2006 7:12 am
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Ed, will you indulge me for a minute, and back up to your previous topic? I was left somewhat confused.
I posted:
"The 25" scale would have greater tension along its scale length but less total tension than the 30-1/4" string (24" scale).
The key factor is tension per inch.
The 24" string would have the same tension per inch in its scale length and its overhang. The two segments must have the same lbs/inch in order to have stasis."
Using lbs/inch instead of psi (assuming a given string guage), my thought was that adding the overhang tension to the tension of the scale length would produce more total tension in the longer string (breakage not being a factor in my thinking).
There was disagreement with part of my statement; and the topic being closed before I could verify my thought, I'd appreciate you're giving me a reality check.
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Eric West
From:
Portland, Oregon, USA, R.I.P.
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Posted 7 Jul 2006 9:26 am
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Simple.
You don't "add" the tension.
If the overhang were a MILE LONG, the string would have the same tension ANYWHERE ALONG IT in order to get the scale length up to the desired tension in the scale area to the desired pitch. A MILE LONG.
The ONLY difference is for each inch of overhang there is the exact same PROBABLILTY of breakage as every inch of the scale length.
So, if the overhang was just as long as the string, the string would only be twice as LIKELY to break in the course of say 6 months. Slightly less, since no scale area strings are not subject to fingerpick, changer use or bar wear.
Scale length DOES relate DIRECTLY to string tension. Total String length in an "overhang" DOES NOT.
Why this has been such a gruelling process of trying to get the simplest physical states properties across is WAY beyond me.
Or not..
EJL
Remember, the company that put out whatever information to the contrary inre to lessened string tension with less "overhang" WENT BROKE and until the company got sold at auction, they couldn't even post straight information on what was going on.
I was there at the auction, and passed on buying it.
I'm glad that it's in GREAT hands NOW.
[This message was edited by Eric West on 07 July 2006 at 10:30 AM.] |
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ed packard
From:
Show Low AZ
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Posted 7 Jul 2006 9:56 am
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Charlie…The problem with describing the tensioned string thing coherently is that the words have different meanings to different people. It is a challenge to discuss. Let me use this as an opportunity to try for a better description.
Take a given string, anchor it at one end, and apply tension to the other. The string stretches according to the tension applied. Each inch of the string stretches by the same amount. The anchored end has zero motion…the middle of the string shows half of the total stretch, and the end that the tension is applied to shows the total amount of stretch caused by the applied tension. The string will vibrate at a given frequency (fundamental = f1). We have a length of string, an amount of tension (pounds pull), an amount of stretch (giving a new string length and slight reduction in string diameter), and a resulting frequency.
If the pounds pull is increased, the frequency go up, the string gets longer (a bit), and the diameter decreases (a bit).
If the pounds pull is decreased, the frequency goes down, the string gets shorter (a bit), and the diameter increases (a bit).
Now lets apply a tension (pounds pull, let’s use 30 pounds) to a given length of string (let’s use 24”), to get a frequency of vibration (let’s say 440 Hz), and an amount of stretch (let’s say 0.5”). Now put a bar in the center of the string. The frequency of each half (12” either side of the bar) will be the same, and be twice ( = 880 Hz) that of the whole string (which was 440 Hz). The only thing that has changed is the length of the two vibrating parts of the string; the total string stretch, the pounds pull et al are unchanged.
Now let’s grab the string in the center, and cut it at that point. To get the string back to the frequency we had with the bar at the center (880 Hz), we will need an applied tension…it turns out to be the original 30 pounds of pull. We have half the string length, the same pounds pull, half the total amount of string stretch (= equal string stretch per inch of string), giving twice the vibrating frequency. So we can say pounds pull per given string (not inch of string), inches of stretch per inch of string, and the string length are what give us the pitch (vibrating frequency = Hz) of the tensioned string.
Summation = The tension is the same AT any point in the string, the amount of stretch is the same FOR any inch of string, and the frequency change is inverse to the length of the string.
Now let’s go back to the 24” string, and make it 30” long, and apply the same 30 pounds pull….the vibrating frequency goes down, and the amount of stretch increases (both total and per inch).
Place a bar at the 24” point. The long part of the string will now vibrate at 440 Hz. For the same applied pounds pull, and amount of stretch per unit length (inches per inch) of string. We can refer to the 30” as the Total String Length (TSL), and the 24” as the Scale Length (SL). Surprisingly, we might treat the 6 “overhang (30”-24”) as a scale length also. Pick it and it will vibrate at 4 times the frequency of the 24” section….but it has a 24” overhang.
The resulting conclusion is that for a given string, Scale Length determines the required Tension (pounds pull, which will be the same AT any point in the Total String Length, and Scale Length), and the amount of stretch, which will be the same FOR each inch of Scale Length…and this is what the basic string tension/length vibration equation says. Total String Length is only part of the happening when TSL = SL, otherwise the difference must be considered as an SL all by itself.
Long and detailed…hope that I said it correctly. The subject is worth some effort because it is one that is confusing. Your beliefs It won’t change your picking style.
OK Charlie, with that as background.
Quoting you:
"The 25" scale would have greater tension along its scale length but less total tension than the 30-1/4" string (24" scale).”
From the description above, we tune according to scale length, not according to Total String Length.
I would reword it to say---a 25” scale, with a given string, tuned to a given pitch, would need more pounds tension applied than a 24” scale would. They would both end up with the same amount of stretch per inch of string. The longer SL requires the increased tension to get to pitch.
“The key factor is tension per inch.”
If you mean …a key factor…per inch of scale, I can agree. The only thing that remains constant in both cases, and for TSL and SL, is the amount of stretch per inch of string, and PSI….did I say that rightly?
“The 24" string would have the same tension per inch in its scale length and its overhang.”
If you mean that if you cut the overhang off (or shortened or lengthened) it, you would still apply the same pounds pull (tension) to the end of the string to get to the same pitch…then yes.
“The two segments must have the same lbs/inch in order to have stasis.”
Stasis = 1. A state of balance, equilibrium, or stagnation.
I think that the Equality here is in the pounds per square inch of string, which produces a given amount of stretch per linear inch of string. If the string was a rod/board pivoting on a fulcrum, then the pounds times the length on both sides of the fulcrum would be equal…not sure how to visualize that in the present context.
“Using lbs/inch instead of psi (assuming a given string guage), my thought was that adding the overhang tension to the tension of the scale length would produce more total tension in the longer string (breakage not being a factor in my thinking).”
By the above arguments (reasoning) that I have tried to show that changing the TSL to SL ratio does not change the applied tension required to get to pitch with a given string, I can’t agree with adding lbs/inch of tension of the TSL to that of the SL.
Not sure how much of that blurb qualifies as a “reality check”.
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C. Christofferson
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Posted 7 Jul 2006 12:56 pm
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| Aren't ALL the factors that go into the harmonic content of a plucked string - where picked, intensity picked, picked with plastic or metal, not to mention a thousand other factors that none of us knows about - infinitely variable and never exactly the same twice. How boring life would be if it could be measured and predicted with an occiloscope. Just pullin' your chains. Now, as you were saying... |
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Charlie McDonald
From:
out of the blue
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Posted 7 Jul 2006 1:03 pm
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Yes, that works fine--a good reality check from both of you.
Yes, it must be a question of coming to terms; I thought it was a simple matter until the explanations and disagreements got longer.
I think we're on the same page now(that scale length is the determining thing about the previous discussion, and overhang irrelevent); I was just unsure for a moment.
Thank you. |
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Joseph Meditz
From:
Sierra Vista, AZ
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Posted 7 Jul 2006 1:19 pm
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Quote from Charlie,
"The 25" scale would have greater tension along its scale length but less total tension than the 30-1/4" string (24" scale).
The key factor is tension per inch.
The 24" string would have the same tension per inch in its scale length and its overhang. The two segments must have the same lbs/inch in order to have stasis."
Charlie,
I think I understand what you are getting at.
You appear to be integrating tension per inch to get total tension. You can't do that.
The tension in pounds over the total length of the string is the same as the tension in pounds over a fraction of an inch of string. For example:
Suppose you stand on your bathroom scale and read 180 lbs. Now, suppose you have a second bathroom scale and stack one scale on top of the other and stand on the stack. Both scales will read 180 lbs!
The difference is that the total deflection of the sum of scales will be twice that of a single scale.
Hookes law says that:
F = kx
The force (compression or tension) is equal to k, the spring constant in lbs/in, times the distance the spring is compressed or stretched.
If the bathroom scale moved 1" while standing on it, its k = 180/1. This is a constant whether the scales are used indivually or in a stack.
But, the spring constant of the entire two scale system is now exactly half that or k = 90/1.
This means that when stacked together, 180 lbs compresses the system by 2".
You can do this experiment: Hang a cup on a rubber band and measure the elongation. Then tie two rubber bands together and do it again. The elongation will double. Also, if you put your finger on the knot the upper rubber band of the two, it will vibrate at the same rate as the single rubber band.
In summary, keeping the scale length constant, increasing string overhang only decreases the k of the system from the tuning peg to the bridge. But the tension does not change.
HTH,
Joe
[This message was edited by Joseph Meditz on 07 July 2006 at 03:32 PM.] |
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Curt Langston
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Posted 7 Jul 2006 2:13 pm
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Edited because I was totally wrong..........
And you guys are right. TSL does not contribute to premature string breakage.
Sorry guys.
 [This message was edited by Curt Langston on 10 July 2006 at 09:46 AM.] |
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Eric West
From:
Portland, Oregon, USA, R.I.P.
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Posted 7 Jul 2006 2:32 pm
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Well luckily "we" can stop right here.
quote:
That is what happened to Buddy Emmons and the 25 inch scale Sho-bud. That extra 1 inch length (TSL)..
-CL-
NO!
TSL= TOTAL STRING LENGTH.
NOT SCALE LENGTH.
SCALE LENGTH DICTATES HOW MUCH TENSION THERE IS ON A PSG. NOT TOTAL STRING LENGTH.
JEEZ OH WEEZ!
If this whole thing is somebody mistaking "Scale Length" for "TOTAL String Length", (TSL) then it points to a group imperative to refuse to debate until this basic misunderstanding is cleared up.
Shame on us.
EJL
[This message was edited by Eric West on 07 July 2006 at 06:16 PM.] |
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Joseph Meditz
From:
Sierra Vista, AZ
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Posted 7 Jul 2006 2:46 pm
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Curt,
I am sorry for this misunderstanding, but I quoted Charlie quoting himself and it looked like a quote from me! I have since edited it.
Charlie is mistaken and is trying to understand why. The tension does not increase from increased overhang.
Below are two ASCII drawings of two systems of equal scale length. The string hangs over a roller o. The x anchors it. The weight provides the tension. The first system has more overhang than the second. Neglecting friction it is axiomatic that the tension in the string is the same in both cases since the weight is the same.
o----------x
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_
/ \
---
o----------x
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_
/ \
---
Joe
[This message was edited by b0b on 07 July 2006 at 05:17 PM.] |
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Curt Langston
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ed packard
From:
Show Low AZ
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Posted 7 Jul 2006 7:14 pm
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OK, onward and upward into the world of PSG construction and resulting signals.
http://s75.photobucket.com/albums/i287/edpackard/ should get you to the photos of the changer/pickup end, and the Keyhead/keyless end of 30 or so PSGs ranging in age from 1 year to 3 about 33 years old.
These are just the top side photos. Photos exist for the undersides also, but a step at a time.
From these photos, one may see the progression of construction and mechanisms over the years.
We have the signal from the pickup for each of these instruments...construction and mechanism may be associated with the signals from the pickups after the Harmonic content vs time charts are posted (soon). |
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ed packard
From:
Show Low AZ
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Posted 8 Jul 2006 8:04 am
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| Reply moved to the Curt's experiment thread. [This message was edited by ed packard on 08 July 2006 at 09:12 AM.] |
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ed packard
From:
Show Low AZ
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Posted 8 Jul 2006 10:39 am
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Here is a quick sanity check (mine) to see if things go right.
This graph shows the harmonic content of a single string, having a "fundamental" of about 300 Hz. The string was open, and was picked at the 12th fret. Picking the open string at the 12th fret will cause the 2nd, 4th, 8th etc harmonics to be lower than if the string was picked elsewhere.
What you are seeing is the "tone" of the open string. If any of the peaks change in height, the tone will sound differently.
This post is to see how the graph shows up, and to begin to make a common language for the subject.
We will refer to the fundamental as h1 = 1 X the fundamental frequency. h2 will be 2 X the fundamental frequency, or 2 X h1. h3 = 3 X h1. and so on.
Using h1 as a root note = I, h2 is an octave higher. h4 is an octave higher yet, and h8, h16, h32 are the same note name at higher octaves....double the frequency, go up an octave in pitch.
h3 is 3 X h1, therefore not an octave, or a note of the same name. It is a V note. If h1 were C, then h3 would be G. h3 X 2 = h6 which is also a V note (G in the example)...h12 = 4 X h3 and is also a V note, and so on.
h5 = 5 X h1, and turns out to be a III note, therefore h10, and h20 are also III notes. If h1 is a C, and h3 is a G, then h3 is an E. We now have the basic three notes of our C triad chord, and all present in the single open string at the same time.
If you look at the chart, you will see the the amount of output from each string varies, and then they all fall off in amplitude as the frequency gets higher. It is at the higher frequencies that the loading of the volume pedal, effects, or amplifier begins to have an effect upon your tone.
Remember that this signal was taken after the pickup had done its job of modifying the raw string vibrations. The pickup did this in two ways. First via it's location re string length. Second via it's electrical network...it is an electrical filter and affects different frequencies in different ways. More on the effect of pickups on the signal later.
[This message was edited by ed packard on 09 July 2006 at 07:07 AM.] |
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 8 Jul 2006 11:03 am
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| To deal with Curt's erroneous belief that total string length creates more tension, I've started a new thread called "Longer string, same tension," so it can be searchable. |
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ed packard
From:
Show Low AZ
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 9 Jul 2006 7:13 am
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| Ed, can you enlarge the graphs a little. It's nice that they no longer make the text run out of the frame, but now they are so small we can't read the numbers. Thanks. |
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ed packard
From:
Show Low AZ
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Posted 9 Jul 2006 7:47 am
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Here is the open string strum at fret 12, on the BEAST, and viewed at the pickup out put. The different curves are for the some of the different pickup combinations on the BEAST. The point is....same hardware, same strings, same excitation, different spectral response because of the pickup used for each trace.
I have reduced the size of the image to fit better with the Forum. The result is that it is now difficult to read values. If more detail is desired, go to the first "Photobucket" link given above, go to the end of page two in the album for the graphs. I will leave the album open to the public as long as the hit rate stays within reason. |
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ed packard
From:
Show Low AZ
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Posted 9 Jul 2006 7:55 am
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DD....looks like I am stuck with too big, or too small with the photo thingy that I have. Go to the Photobucket site via the first link given above, and you can play in the garden. Graphs are at the bottom of the second page of the album...at least as I view them.
Now we will take one of the pickup settings, and look at the spectrum that results as a function of time. We will use 0,2,4 and 8 seconds after the open strings have been strummed. This will give what we hear as sustain. You will notice that the mid/low frequency output changes less than the high frequency out put vs time.
Point 1....the mechanism/construction of the instrument has an effect upon the "tone" = harmonic content, at any time. We will see this when we get into comparing the graphics of response for different instruments.
Point 2....the pickup will change the sound "tone" of an instrument, depending upon the pickups magnetic and electrical characteristics, and its location re the string (height, length).
I have used the BEAST as the source of the information given so far because it quite different in construction, pickup capability, and mechanism as compared to the common PSG. The questions that will arise where we are going will have to do with the effect of construction, mechanism, pickups, et al on "Tone" at time, and tone as a function of time. Here we are illustrating the extreme of differences from the standard.
DD...I think that I have found a compromise re graphic size, but I cannot restore the ones that I have already posted. I will try the other sizing in the next post.[This message was edited by ed packard on 09 July 2006 at 09:37 AM.] |
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ed packard
From:
Show Low AZ
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Posted 10 Jul 2006 8:22 am
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Here is another look at the results of an open string strum excited at the 12th fret, and as seen thru some of the available pickups on the BEAST. We will then contrast that with the same type of presentation, but using the "scrub".
The "strum" was once across the open strings excited at fret 12. The "scrub" is all strings, all frets, all excitable locations, and capture the highest (peak) output for each frequency and each position/location event. In this case, they are shown as seen thru an assortment of the available pickup combinations. Notice that we did not use "smoothing" on the "scrub" outputs...it is not needed as the frequencies in the signals are very close together...indeed the same frequencies are found on each string at different frets, as are the harmonics of each string and each fret when considered as fundamentals.
This last shows just about everything re tone and output that is available using the pickups and hardware on this extreme instrument.
Here are the "hardware" photos of the BEAST, the source of the signals for the preceding graphs. First, the integrated changer/tuner structure. On the BEAST, it is located on the players left.
Second, the nut and pickups...on the BEAST, they are on the players right. The scale length is 29.730", and the Total Scale Length (TSL) is essentially 31.25 or so inches.
These are two pickups, each with taps, and reversible summable windings for a very wide range of tone variations.[This message was edited by ed packard on 10 July 2006 at 09:59 AM.] |
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ed packard
From:
Show Low AZ
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Posted 10 Jul 2006 8:50 am
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We have now reached a milestone in this project...we have shown the methods to be used in analyzing/categorizing the "tone" and "Tone vs. time" for an assortment of instruments.
What has been shown are the frequency and amplitude results of:
1. Harmonics in a single open string, excited at the 12th fret...the source of scale and chord structure.
2. Harmonics from the single string smoothed to make it easier to see/read when combined with other strings outputs.
3. Spectral output of all open strings strummed when excited at the 12th fret, and this output smoothed. Look at the unsmoothed output and you will see "bumps" where the individual strings are. The tuning shows up in these bumps.
4. The effect of pickup type and location on the strum signals.
5. Harmonic variation vs time for one of these pickup settings, and the open string strum excited at the 12th fret.
6. The spectrum available, as seen from various alternative pickup settings, for the open string strum...to be compared with...
7. The spectrum available, as seen from various available pickup settings, for the "scrub".
8. The hardware configuration that produced the graphs of the frequency vs amplitude and time.
Notice the difference of the shape of the curves between points 6 & 7 above...can you explain it? Why do you think that this would be?
There are a couple of twists to the above approaches that will emerge as we proceed. I hope Joe Meditz will be so kind as to keep me straight, and add some of the work that he is doing to expand the subject.
If you think that the TSL/SL/stretch/tension/pitch/breakage was tough to talk about...wait till this stuff starts.
Next we will take an E9 10 string, and compare the available response. Might as well make it the FESSY, as that is what Joe M has at hand.
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Joseph Meditz
From:
Sierra Vista, AZ
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Posted 10 Jul 2006 12:10 pm
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Hi Ed,
A few questions:
Was the intial attack also fed into the TrueRTA for spectral analysis for the single string, the "strum" and the "scrub?"
I imagine that the "scrub" was done by turning on the TrueRTA and setting it to peak detect and then doing an OS "strum" at the 12th fret, then bar at 1st fret and strum at 13th, etc. Is that correct?
What was the highest fret you put the bar at?
You said you recorded the scrub position event info. Does that mean you saved 12 files of data if you scrubbed through an octave?
Joe
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ed packard
From:
Show Low AZ
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Posted 10 Jul 2006 12:51 pm
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Joe...The initial attack is only included in the samples taken in the peak (0 secs) mode. I do not know off hand what the resolution of the Peak capture, or the algorithm used is.
The better way to capture the info would probably be to record the various responses as in recording the music, and THEN capture and analyze the resulting details in whatever data diddling way(s) makes sense. This would be session 2 at Jim's.
Re "scrub"...The peak capture was turned on and the string was randomly strummed while the bar was continuously moved (slowly) up and down the neck until no increase in amplitude was seen. No attention was paid to being ON any fret...in betweens all over the place.
The highest point on the neck was at the pickup. What was recorded was the single file with the max output seen by scrubbing.
Scrub was not applied to the 32 PSGs at Jim's...just to the BEAST to see the difference as compared to strum. The question posed was...if different, how different, and what might be learned by doing it to all.
[This message was edited by ed packard on 10 July 2006 at 02:11 PM.] |
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ed packard
From:
Show Low AZ
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Posted 11 Jul 2006 1:34 pm
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The magnetic pickup is a device that senses the vibration of the string(s), converts the physical vibrations of the strings to electrical signals, and provides access to the electrical by the subsequent equipments through which the electrical signals are modified, amplified, and then converted back into vibrations that we can hear.
What we then hear would seem to be quite different from the first pure vibrations of the basic string.
The magnetic pickup is composed of a physical structure that houses a magnetic circuit, and an electrical circuit. The terms and symbols for the electrical circuit are:
R = Resistance…in Ohms of some magnitude.
L = Inductance…in Henrys of some magnitude.
C = Capacitance…in Farads of some magnitude.
The R is the Resistance of the wire (winding) of the pickup. It is commonly misnamed Impedance. The R varies with the length of the wire in the winding, the size (diameter) the wire, and the material of the wire. Equal lengths, or turns of wire may have different Resistances, depending upon the size (diameter) of the wire…therein is ONE of the dangers of using pickup resistance as a measure of what the pickup will do sound wise.
The L is the Inductance of the winding. It is the link to the magnetic circuit. It’s value will depend upon the electrical winding, and the Windings coupling to the magnetic circuit. The larger the Inductance of the pickup, the less the high frequency signals allowed thru the pickup.
The C is the Capacitance of the winding, and is a function of the wire size, the insulation thickness on the wire, and the type of winding (called layer, random, scramble, etc). All else equal, thin wire gives more winding Capacitance than thick wire…Layer winding gives more Capacitance than the more random types. The larger the Capacitance in the pickup, the less the high frequency signals allowed thru the pickup. If it looks like a conspiracy between the L & C to kill the high frequencies, it is.
When we combine the R, L and C we get an electrical “network” that has parameters that may be used to describe the networks “filter” effect upon the vibrating string(s) frequencies sensed by the magnetic circuit. These parameters and their symbols are:
X = Reactance = like an AC (alternating current) resistance. The lower the Reactance, the less the effect upon the frequency. The Capacitance has a Reactance
(Xc), and the Inductance has a Reactance (XL).
Given values of Xc and XL are different at different frequencies, hence together they form a frequency selective filter. XL increases as frequency increases. Xc decreases as frequency increases. Can you see a “band pass” filter (high in the middle, and low at both ends)? For those that like equations, Xc = 1/(2 PI Hz C) & XL = (2 PI Hz L). The frequency center of the band pass filter is where XL = Xc; that is where the greatest amount of the string(s) vibration frequency as sensed by the pickups magnetic circuit will be passed thru the pickup.
The band pass filter has a property/parameter called Q. The larger the Q, the more selective the filter is re frequency; the lower the Q, the less selective the filter is re frequency. How may we control the Q of the filter, hence the sound from the string(s) vibrations sensed by the magnetic circuit? By the resistance of the wire used in the winding. Smaller wire means greater winding resistance (for a given length and type of winding), hence a lower Q filter and a lower frequency selectivity (flatter frequency response); Larger diameter wire, allows a higher Q filter.
The pickup has a property/parameter called Impedance (there it is!!!!) symbolized by Z. The Z of the filter is different for each frequency….how different? Depends upon the R,L,C,Q,X, and any other vegetables in the soup, the L of which depends upon the magnetic circuit.
What in H (coercivity here) is a magnetic circuit? Most picker folk will think of a pickup as simply some cylindrical magnets surrounded with some turns of wire. Maybe they call the magnets Alnico’s. The magnet(s) may be cylindrical, may be any of several types of Alnico (Aluminum, Nickel, Cobalt) material BUT they may also be one or more long bar magnets, may be Rare Earth, of Barium Ferrite, or other magnetic materials.
Each of these materials has it’s own properties…you don’t want to have the gory details presented here, so we will just say that the type of material, shape of material, and geometry of orientation of the material in the pickup, combined with any possible “return path” (from one magnet pole to the other) creates what we are calling a “magnetic circuit”. It is quite like an electrical circuit in the there is a force, something that flows , and something that something that limits the flow (think garden hose).
The electrical is Volts = Electro motive force, flow = current, Resistance = Ohms.
The magnetic is MMF = Magneto motive force, Flux (Latin for flow), and Reluctance.
The magnetic circuit is positioned such that the vibrating (and magnetically conductive) string(s) is/are in the magnetic field. When the strings vibrate, they disturb the magnetic field causing the flux to change in the magnetic circuit. The winding is in the magnetic circuit, and senses this change in flux, filters it according to it’s R,L,C,Q etc. and allows the “in the band” frequencies thru. What vibrations get into the magnetic circuit, and what determines the output amplitudes from the pickup?
The L of the pickup is a function of the flux coupling between the magnet and the coil. All else being equal, stronger magnets give larger L and associated frequency selective properties. A strong magnetic field round and about our coil may not be what we want.
The string(s) vibrations that get into the magnetic circuit are a function of the shape of the magnetic field where it is disturbed by the string(s) vibrations. If the pickup is located close to the bridge, the strings
vibrations that are found there will enter the magnetic field. Pickup location along the string is a determinant of the harmonic content (ratios) in our final signal. So is the focus of the magnetic field at the string…if a large length of string vibrates within the magnetic field, the sound will be different than if a very short segment of the vibrating string is sensed (think return screws and dual magnets etc.).
Here is a chart showing the vibration paths of h1,h2,h3,h4,h5 of a string, as a function of neck length. The amplitude of all h# vibrations has been set equal. You may notice that h#s that are ODD have a loop maximum at the 12th fret = ½ the neck length, and the h#s that are EVEN have a null at the same place…pick at the loop, get a maximum signal out for that h…pick a null, get a minimum signal out for that h.
Envision the frequency response for the h#s as a function of where you place the pickup re the neck length.
These h1 thru h5 vibrations are, in order R,oct,5,ooct,3, or if the string were tuned to C….C,C,G,C,E.
The larger the amount of disturbance of the magnetic field caused by the vibrating string(s), the greater the output of our pickup will be…all else being equal. Notice that it is the “change” in flux that is sensed, not the amount of flux. Magnet strength takes a back seat to magnetic circuit design when it comes to getting the desired signals to and thru the pickup. A shaped magnetic field at the string interface trumps a strong field.
To make the L low (more highs thru), the winding may be removed from around the magnets, and placed at another location in the magnetic circuit, where the ratio of field strength to changing flux is more suited to getting our desired harmonic content thru the pickup. If we reduce the L by repositioning the winding , we can increase the number of turns, and get more output.
The output voltage is commonly expressed as
Eo = k N (d phi/dt) where:
Eo is the output voltage
K is a constant having to do with pickup structure, efficiency, et al.
N is the number of turns.
d means “change in”
Phi is the magnetic flux.
T is time.
Now we will consider how to get the signal out of the pickup. We have seen that the electrical network of the pickup has an “impedance” = Z that varies with frequency. If we place a load (like a volume pedal) across the pickup, we may well reduce the high frequency transfer because the pickups output Z is much higher at the high frequencies than at the lows.
Now place/attach an amplifier (or effect, or ?) across the volume pedal. When the pedal is full on this new Z becomes part of the load that the pickup sees…you have lost more highs, and the tone varies according to how low the amplifiers Zin is, and how far you have pressed the volume pedal.
To make the analysis of the 32 PSGs constant, we will load the pickup(s) with a 500KOhm load…like a common pot volume pedal presents with nothing else attached.
Those readers that come from the age of tubes and output transformers may remember the the unloaded output transformer had a bit of an increase in the output of the highs. This was the “undamped” case. The degree of damping (loading) determined the shape of the high frequency response in the vicinity of the falloff slope.
The pickup is very much like the secondary of the output transformer in the above analogy….the same bump occurs if the output load is left off.
We will use the pickup(s) that are on the PSGs to see if we can quantify what sound it is that the various types of pickers want/like. There will be several categories.
Then we find it a good thing to do to use one positionable pickup to see if we can identify the contribution of the various constructions et al to the sound differences of the instruments.
Bottom line = we have magnetic filters, electrical filters, spatial filters (where the pickup is mounted re the string), material/construction/geometric/coupling filters (both PSG structure, and the magnetic structure of the pickup. Pickups also have “micro phonics”, so how the pickup winding is damped (wax or?), and how it is connected to the instrument is another “filter” source.
And then there is hum….never mind…enough already!
Why all this about pickups? Because, on the same instrument, the chosen pickup makes a big difference.
In our 32 PSG analysis, we just took the instrument and pickup as they were at the shop. This means that if we see a big difference between EMMONS PP and another EMMONS PP of the same generation, we don’t know how much is due to instrument, how much to pickup structure, how much to pickup mounting…but it is a start. The obvious details of the pickup structures, mounting, and resistance were taken. The changer end photos allow you to see the pickup and its location re the string end.
The photos of both the changer, and nut/tuner ends allow you to see the physical differences between the PSG string terminating/body connection approaches…THINK FREQUENCY FILTERS…THINK TONE!
If you see something that looks stupid here, it probably is...let me know.
Thanks for the XL,Xc correction JM!
Again, as these graphics are added, they are all available in one spot = the first PHOTOBUCKET link. Someone seems to be reading this stuff as there are roughly 1000 hits per week at PHOTOBUCKET.[This message was edited by ed packard on 12 July 2006 at 08:34 AM.] |
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ed packard
From:
Show Low AZ
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Posted 12 Jul 2006 9:44 am
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NOW TO BEGIN THE COMPARISON OF THE INSTRUMENTS.
This post will be periodically updated (edited) as we continue. check back to it from time to time.
Some of the comparison methods and presentations have been presented above, in the previous posts in this thread. We start with photographs of the changer end, and the tuner end of the instruments. Then we proceed to the FSA graphs/charts.
Our first comparison, will be a FESSY, owned by Jim West (thanks Jim), and an EMMONS PP. Here are the photos.
The FESSENDEN #2 ON OUR 32 PSG LIST...CHANGER END.
The FESSENDEN #2 ON OUR 32 PSG LIST...KEYHEAD END.
The EMMONS PP #3 ON OUR 32 PSG LIST...CHANGER END
The EMMONS PP #3 ON OUR 32 PSG LIST...KEYHEAD END
The first very noticable difference is the appearance of the pickups. The FESSY has two rows of magnets, and the EMMONS PP has one. You might also notice that the diameter of the magnets is different.
There appears to be a difference in the diameter of the roller nuts...maybe even groove shape...TBD.
Jim Palenscar made detailed measurments on the PSGs used in this analysis. We will present a listing of those measurements, and more, for all of the instruments before starting with the FSA graphs/charts. The list will be in several pieces, by category of PSG physical area, such as cabinet, changer, pickups, etc.
Here is the cabinet info list:
Here is the rear apron and neck info list:
Here is the changer and nut info list:
The lists will be continued in the next post because the maximum images per post seems to be 8.[This message was edited by ed packard on 12 July 2006 at 05:27 PM.] |
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