Vibrations

[ed packard]

CHART, BOARD SCRUB, STRUM, REF, PICK.



A quick explanation of the traces and method:

The top traces are the “SCRUB” (= peak output of all strings at all frets excited at all frets with a thumb pick. And a ZIRC bar). This shows all that the system has to offer for the excitation methods. One trace is the other (raw data) smoothed for ease of viewing. It shows how smoothing affects the unsmoothed data.

The next traces are the “STRUM” (= peak output of all strings at the open fret, excited by a thumb pick). This shows all that the open string strum can give for the excitation method employed. One trace is the raw data, and the other is the smoothed version of the raw data.

The straight line trace is the calibration trace for the measurement channel sans the instrument under test.

The bottom trace is the pickup output for the open single string excited by a thumb pick at fret 24.

The above CHART shows the “signatures” for the BOARD, for the excitations applied. What is NOT shown is the STRUM response up the neck, and the Spectral Decay response at times after excitation (2,4,8 seconds…think “sustain”).

The SINGLE STRING trace(s):

The single string trace (bottom trace) will show the relative maximum amplitude (peak capture) of the harmonics for the string chosen. This amplitude varies as the excited string rotates. This is NOT available in the single string trace…it needs to be seen in real time, but can be captured in video.

The single string trace can also be used to determine the consistency of the excitation, answering the concern for the need of a mechanized picking/exciting machine = don’t need it at this level.

One may also see the harmonics’ level re the REF trace, showing the absolute values and the resolution of the excitation.

Also available is the adjacent string vibration caused by any sympathetic vibration effects, or connection thru the nut and or bridge materials….think string separation.

And then there is the 60 Hz hum; This may be seen toward the left of the trace and should be 40 or so dB below the peak signal.

The single string trace may be done for any/all strings to show the relative harmonic levels between the strings.

STRUM:


The STRUM trace shows the highest outputs (peak hold) for all the strings when excited together. All harmonics for all strings are captured. The bumps along the top of the trace are related to the particular tuning. The BOARD is tuned to E6 = E,G#,B,C# repeated 3 times.

The strum may be repeated at frets up the neck to see if there any differences as a function of bar position…this means that we need to compare the open fret strum with a first fret strum to determine and bar effect, and this means that we can use the method to compare bars. The bar used herein is the ZIRC.

SCRUB is described in the first paragraph of this post.

We are sneaking up on the attack, dwell, and decay signature measurement methods = “sustain” etc.

[Brint Hannay]

I don't seem to be able to get the concept of the "scrub."
When you say "peak output of all strings at all frets excited at all frets with a thumb pick. And a zirc bar," I can't picture what that means. Does the trace sum up the results of a series of strums, one with the bar at each fret?

[ed packard]

Brint...NOT sums, but presents/retains the highest value of each frequency (fundamentals and overtones/harmonics caused by exciting all strings, all frets...and between frets. Then this is smoothed if desired.

Good tutorial and more. RTA allows monitoring/measuring everything from the pickup, thru the amp, the speaker, and the room...all with the same device and methology.

http://www.avsforum.com/t/572477/truerta-for-dummies

[Curt Langston]

Hoo! I need a cup of coffee!

[Henry Matthews]

Holy Mackerel, just read most of this thread and a lot of time and trouble gone into. What I want to know is, how can we tell on the graph where the perfered sound is that makes us love a particular guitar?

[ed packard]

Henry M…What…no ZIRC bar?
Where in the CHARTS to look for XX depends upon what the XX is that you are looking for. It might be attack, it might be dwell, it might be spectral decay, or what is left over = “sustain”…and you might want the sustain to be in a particular part of the spectrum. Harmonic magnitudes vs frequency, and the magnitude changes vs time will supply most of this info. Then there is the vibration to be found in different parts of the instrument. Paul F likes to feel the vibration in the legs at the floor. Might as well hear it by using a contact mic, or the old mechanics trick of putting a screw driver into your ear and placing the tip at the places of concern…maybe a stethoscope, then the vibes are heard as well as felt. More on the CHARTS vs XX will follow.

Ignoring the appearance, fit, and feel of the instrument, different sounds are better for different music. Much of the sound control is in the player’s hands and body. Different instruments provide better vehicles for certain styles. What makes them “better” is a matter of harmonic content vs time = attack, dwell, and decay profiles. John Hughey reduced the attack parameter using his VP on “Look at Us”….J D Maness emphasizes attack in the chase scenes of “DUKES of HAZARD”. Then there is the “smooth” sound of Bill Stafford as the PSG only background for the movie “My Own Private Idaho”, and his PSG CD “Going Home”.

Bottom line = If we can consistently reproduce the harmonic content as a function of time CHARTs, then we can learn to associate the visible with the audible, and from the traces see which instrument will allow best sonic/vibrational fit with the desired type of music.

You may nave noticed that most of the CHARTs are from open string info excited at a particular fret by a thumb pick. This is done to minimize the people and equipment effect on the data as we are here interested in the capabilities of the instrument, not in the player.

Regarding picking consistency…use your thumb pick and push a string sideways. You will find that the force required to displace the string increases quickly as the displacement is increased = easy to be consistent when using the strum with a thumb pick.

For those that might want to improve further, take a number of readings, throw out the highest and lowest (the “outlyers”), and average the rest. RTA has an average function in the “utilities”.

George and other interested folk: The BOARD is toast…I loosened 8 screws and transferred the nut and bridge hardware to the FRAME. Then moved the pickup plate that is soft mounted and adjustable in the Z axis (how close to the strings). The first photos have been added to http://s75.photobucket.com/albums/i287/ ... ?start=all

Here is the basic shot:

[Henry Matthews]

Hey Ed, didn't mean to come out sarcastic but you explained it very well what I was thinking. You've really put a lot of work into this. And nope, no zirc bar, but if they would help, I'd sure try it.--- Henry

[ed packard]

HM...Nice collection of D-10s. Does any one do it all for you?

[Henry Matthews]

Right now I'm playing the Mullen out and at home and my Zum is set up down at the Opry where we have a regular Sat. Nite show. The ZB is all apart but it really sounded good before so waiting to see how it is when I get it back together. As far as a favorite, don't really have one all the time. Next month it may be the Rains and then the Zum and then the Mullen. They are all great guitars but just a little different, each one of them. Shucks, I guess I love them all, lol.

[ed packard]

The energy in a vibrating string will be reflected back into the string by the nut/bridge rods, transmitted across the nut/bridge rods, absorbed by the nut/bridge/frame, radiated as pressure waves in the air around the string, or radiated as heat from the string.

Picking a string produces an output from the pickup that will last as long as the reflected energy allows. With the screwdriver in the ear trick, or the contact mic we may check the amount of transmitted energy (in the part of the string between the nut/bridge rod and the strings terminating point) in the individual string, and it’s degree of isolation from the adjacent strings. We may also check the frequency band of the energy in the nut/bridge assys, and at various places in the frame.

Each section of the above is a “filter” of some type. They will have individual resonant points, and group/system resonant points in the spectral band. These resonant points, and their Q (how peaked they are) when summed up will determine (phase included) Attack, Harmonic content, Dwell, Decay, and what is called “sustain” = last note standing.

Sound waves (pressure waves) travel at different velocities in air, water, different solids etc.. The SG/PSG structures are made of solids of some types. If the filters caused by the material/shape etc. have a high Q at some frequency, they may be said to have a high impedance at that frequency, and will require less energy to make them resonate = less energy taken from the string, hence the longer that/those string(s) will vibrate. If you want some fun diddling numbers, look up the sonic transmission properties of the SG/PSG materials and calculate wavelengths etc. these properties of materials are used in NDT= Non Destructive Testing of materials and assemblies.

Back to the CHARTS.

We have illustrated some of the waveforms that may be obtained using the described methods related to the FSA/RTA software and the SG/PSG hardware = strum, scrub, pick. These gave the peak values at time 0, now we will major in strum smoothed vs time to get the Attack, Dwell, Decay, and “last note standing” = sustain. These were the tests run at Jim Palenscar’s shop on the 30 PSGs in 2006. The strum was applied to each instrument, and the output recorded for 0, 2 4 and 8 secs. The load on the pickups was several meg ohms. The data collection may be viewed at http://s75.photobucket.com/albums/i287/ ... STRUMENTS/

Several of these CHARTS for smoothed pickup outputs vs time will be used here to discuss some of the information hidden in the traces.

The first CHART is from JDs Emmons PP.

CHART…JDs EMMONS PP.


The neck used is the 10 string E9 neck. The lowest fundamental of the open string tuning is B3 = 124 Hz, so all lower frequency content is not from a vibrating string.

Look low and to the left and see a bump at 60 Hz. This indicates the level of “hum” susceptibility for this instrument.

Look at the distance from the top trace to the next trace down. This indicates a large volume drop from the time 0 (excitation time) to the 2 second dwell time. Looks good for an aggressive Attack response.

Look at the far right of the top trace. Notice the level of high frequency response, and the bump just before the rolloff. This bump is common to unloaded (undamped) resonant circuits. The roll off would start sooner if the 500K ohm VP were added.

Notice that the three lower traces are more closely grouped in the lower frequencies than the top trace…and last longer at this spectral. Is this an index to “sustain” time and spectral location.

NEXT…compared to a couple of other PSGs.

[Donny Hinson]

Ed, what is the rreason for the 60hz bump to be so wide? Having dealt with power systems in the past, I know that the source frequency regulation at the power company is incredibly precise, but the graph seems to show a large component, possibly 40hz in width.

[ed packard]

Hey Donny,

The broadness of the 60 Hz bump is a function of the "smoothing" value that I have chosen to use...a smaller smoothing value would give a narrower resolution band, until we get to no smoothing which is the raw signal. Look at the first CHART on this page (6). It shows the raw strum signal with the smoothed version superimposed. The resolution of the raw data is sacrificed to avoid info clutter via smoothing.

The accuracy and resolution of the $100.00 software (TRUE RTA)is a function of the chosen FT (Fourier Transform)implementation = more than sufficient for the task at hand.

The 60 Hz environment at the test site (JPs shop) was at the same spot with the instrument orientation the same for all instruments. The bump height would be different if the environment were different.

If we profiled the "noise floor" for each instrument the "noise" would include the amount of 60 Hz getting into the loop, and also any other noise in the area.

"Smoothing" causes the broadness in the 60 Hz bump.

[Tony Williamson]

there are two mediums related to sound wave travel relevant to all of us. air, and ear wax. i say again , you hear with your ears, not your eyes. i see a lot of people fighting evolution. natural evolution of the steel guitar. my beautiful red superpro dont sound near as good as my tricked out ldg, with a telonics pu and williams undercarriage. but im not unhappy with it.i just cant afford to experiment, and i wouldnt trade it for anything, except that blue emmons p/p ive seen on here for sale. wow what a thread. you guys are some smart crackers.

[ed packard]

Tony W..."CRACKER" sir?...I will have you know that I have never herded cattle in the Georgia/Florida area with a whip!

Is there a better way? Yes! The 0,2,4,8 second traces were timed with a stop watch. This means the strum must be made, and the RTA stopped at the desired time = a lot of movement going on almost at the same time. Each time gets its own strum = some variation introduced…this is how these traces are taken.

The better way is to use the ZOOM R24 to record the full results of a single strum, then play it back at the various desired times by setting a loop at the 0 sec, 2 sec etc. mark and send that to the RTA = more flexibility, and more accuracy. Most DAWs could be used for this also.

For now, I will use the “old way” just to be consistent with the data already taken (almost).

We have taken a quick look at an EMMONS PP that was 37 yrs old in 2006, now lets compare to a FESSENDEN that was 3 yrs old at the time, and an EMMONS PP 1966.

CHART…FESSENDEN U12:




CHART…EMMONS PP 1966:


First the 60 Hz bump. It is missing on the Fessy because the low string vibration covers the 60 Hz range.

Second, the top trace far right bump is a bit more prominent on the Fessy and the 66 EMMONS. Probably a pickup difference issue.

Third, Notice the differences between the top traces and the next lower (2 sec) traces…an indicator of attack differences?

Fourth, look at the grouping of the bottom three traces…indicates the change in tone vs time by way of changes in spectral amplitude.

Fifth, check the retained amplitude area at the left of the traces…indicator of the spectral location and broadness of the “sustain”.

Now a look at a Sho Bud (they do not all look the same)

CHART Sho Bud:


And then there is the BEAST:

CHART…the BEAST 14 string 30” scale and other differences from standard PSGs.



Any comments on “sustain”?

If you would like to compare the rest, along with the mechanicals that made them, go to the bottom of the album: http://s75.photobucket.com/albums/i287/ ... ?start=all

That should be headaches enough for one day.

[Pete Burak]

...Any comments on “sustain”?...

If "Blocking" is so important, why care about Sustain?

[Georg Sørtun]

Interesting "high strings" sustain in the Sho Bud compared to the others.

[ed packard]

Pete...they are SG pickers...that should explain it all.

When I play folks "block" their ears = ear blocking!

Georg...looks to me like the pickup might be close to the strings and the back end not = tilted. Check the other Sho Buds in the PhB file.

[Curt Langston]

The broadness of the 60 Hz bump is a function of the "smoothing" value that I have chosen to use...

Ahh.... the old, chosen, smoothing value......

Indeed. I should have known.

Now. Where's that cup of coffee!

I'm 'bout to fall out here!

[ed packard]

Here is a vibration measurement take on the REAR LEFT LEG of the PST 13 unit (14 strings). Taken at about 3" from the floor when the instrument was excited with a n open string strum.

[ed packard]

The PST 13 is a SIERRA SESSION series instrument.

The REAR LEFT LEG vibrations shown above is energy that has been lost from the strings. Notice that the vibrations extend beyond the 2 KHz roll off seen from the pickup. This same kind of lost energy from the strings can also be measured on the aprons, the end plates, and even individual string extensions (beyond the nut and bridge), and any solid surface on the instrument. Some of the instruments tone providing capabilities have been lost from the strings. Can we reclaim some of this energy for use with that still in the strings? Yes indeed. See if you can figure out how.

[ed packard]

RECLAIMING THE LOST ENERGY:

The sound coming from the SG/PSG is the vibration(s) of the strings minus the energy transmitted, absorbed, etc. (in other words reflected/radiated) and modified by the limitations of the particular pickup. The common pickup is a band pass filter, losing some of the low and high end frequency content. The common pickup roll off on the high end is generally about 2KHz for the 0 sec capture, and falls off quickly until all that is left is in the 100 to 300 Hz band…we call this the “sustain”.

The rest of the vibrations get distributed into the body, clear down to the tip of the legs. The leg tip vibrations are shown for the SIERRA SESSION series instrument in the last CHART.

Let’s look at the vibes in some of the other parts of the instrument and notice the part of the spectrum that they inhabit. These locations include the front apron, end plates, rear apron, leg tips, etc.. Notice that the body energy is mostly at the high end of the spectrum…in fact it is mostly in the area of the “decay” = >2kHz.

PST 13 BODY VIBEs vs STRUM CHART :



The top left/bottom right green trace is the STRUM for the PST 13. The other traces are the vibrations from the aprons, end plates, legs, etc of the PST 13. The strum trace starts to roll off at about 2KHz. The body vibes increase from 2KHz to 5 or even 10KHz. This is the area of the spectrum being (milked = lost) from the strings. These can be reclaimed by using the contact mic (or sim’) and merge the result with those of the standard pickup.

Using the body vibes via contact will also pick up the ped/lev noise = not good for most PSGs, but OK for SGs. Using a non mechanical pitch shift system instead of the common ped/lev mechanics solves the body vibes induced mechanical noise problem.

TEST METHOD:

The body vibration signatures are taken with the contact mic that came with the PETERSON VS-II tuner. The mic signal is sent to the CH2 input on the R24. The pickup output is sent to the Hz CH1 input on the R24. CH2 volume is raised to the approx signal level of CH1 (a convenience for viewing/listening. CH1 & CH2 are combined for the output. Open string strum was used for most tests…Individual string and “up the neck” were also observed but not shown above. The contact mic signals were in the harmonic structure of the string signals.

CONCLUSIONS:

High frequency losses found in the pickup output are coincident with the high frequency presence found in the body vibration signatures = high (>2kHz) are transmitted from the strings into the body . This being the case, we can recover them if we like and restore them to the string signal (as was done above).
Other noises found in the body, such as squeaks etc. from activated pedals and levers may be studied, and improvements investigated (reduce moving metal on metal contact for instance).

If we could confine the vibrations to the strings (total reflectance) do you think that the present common pickups would be up to the task?



I don’t like mechanical systems attached to the body…they will add noise. Using a contact mic (or accelerometer) against say the front apron and listening to the result while using the pedals will show squeaks from metal on metal etc…it would be nice to eliminate that. The link above is a thread on vibrations (on going) in the SG/PSG.

A system exists for using a contactless sensor for ped/lev position. The output voltage is used via an ADC to a uC. The other input(s) to the uC is the individual string output(s) from the “semiconductor” pickup. “pitch shift” is used as an electronic changer. Whole tunings can be changed, as well as individual, or groups of strings without changing string tension or length. The ped/lev sensors are single channels from the semiconductor pickup: More info here:

http://s75.photobucket.com/albums/i287/ ... ?start=all

Presently, retuning an E9/B6 universal to C6, Bb6, A6, etc works fine…as does raising up to one octave,, and lowering up to two octaves. The lowering allows replacing wound strings with plain strings to eliminate string noise and also the quick falloff of harmonics on wound strings. Much more.