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 Post subject: PSG understanding and development overview:
PostPosted: Fri Jul 22, 2011 12:17 pm 
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Joined: Tue Apr 19, 2011 10:54 am
Posts: 76
Location: SHOW LOW AZ USA
There are a plethora of “opinions” and street wisdom re PSGs available on various Forums and platforms like You Tube and “news letters”. These all serve the good purpose of keeping the PSG pot boiling, and also the less good purpose of adding to mythology re the instrument.

Nostalgia, tradition, and love of the “good old days” tend to heap accolades upon certain instruments and players of the past….some deserved, and some not as much. PSG players, like all humans have their better and worse sides, and PSGs have their good and not so good physical and tonal attributes.

Leaving the psycho and social characterization of players to others, I will cast a vote for the use of modern instrumentation techniques and equipments to define the performance attributes of old and new models of the PSG. We started down this path in 2006 at Jim Palenscar’s shop where we analyzed the sonic performance of 30+ PSGs using the Frequency Spectrum Analysis software to profile and quantify the produced spectrum and its change with time (decay/sustain) for certain methods of string excitation. The physicals and dimensions/materials were also recorded. You can see some of the results at this link. XXX to be added later.

To address the hand waving arguments re what is good for sustain and tone, an “breadboard” instrument was fabricated the had a 30” scale length, no neck block, two tapped interchangeable pickups, integrated keyless tuner and changer, the changer placed on the players left, a simple interchangeable bridge, a different string attachment/anchoring system, and so forth. These changes/differences attacked the issues of string length vs. sustain and tone, variations in pickup characteristics and location, on sonic parameters, and so forth…including some material issues like brass vs. aluminum, vs. Zirconia for bridges etc.. An extruded aluminum body was chosen because it is more sonically consistent than the various woods, and has a thermal coefficient of expansion more closely matched to that of the string material. This “thing‘ has become known as the BEAST, and is included in the 30+ PSG analysis. You decide what effect if any all or any these differences had upon the “sacred cows” of construction.

The limitation of the methodology used in the analysis of the 30+ was that the data was in the form of a series of sonic “snapshots”. This meant that the info available for analysis was limited. What is needed is a sonic “movies” (calibrated recordings) which can be used to analyze things thought of later and with the flexibility of local looping of signals etc. while subjected to FSA and similar. To this end, I have added the Zoom R24, and Sonar X1 to the analysis arsenal = record the results of PSG excitation into a Hi Z channel (minimize pickup loading), and analyze as convenient. Eventually the sonics may be heard at the same time the visuals are presented. The existing equipment is shown at the following link: YYY to be added later.

With these capabilities in hand, we are equipped to analyze the PSGs of the past and present…this coupled with the ability to apply Finite Element Analysis (FEA) type modeling of structures and magnetics give us powerful tools for the development of future generations of the PSG.

Areas for development are:
Alternative pickup types.
Pickup signal processing methods.
Alternative changer methods…electronic changers (with and without mechanics).
Pedal and Lever electronic position sensors.
Alternative volume control methods.
uC on board signal processing.
Wireless from PSG to Amp/Preamp etc.
LCD fret board, computer controlled.
Tablet/tablet PC as PSG dashboard for touch control of PSG related apps etc.

Pick your project!!!


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 Post subject: Re: PSG understanding and development overview:
PostPosted: Fri Jul 22, 2011 9:32 pm 
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Joined: Sat Dec 11, 2010 11:44 am
Posts: 517
Location: Gallatin, Tennessee, USA
Ed -

My "mental" project would be: What does and what does not contribute to or is the detriment to "tone".

You've heard me laud the virtues of a particular PSG in Seymour's shop. Why is that particular instrument possessive of unusual - and to my way of thinking - extraordinary and exciting characteristics as regards tone when the remainder of the thirty-odd instruments on the floor are relative slugs - samo, samo - ya couldn't give me a one of them.

Why - how - why - how and more why and how?

I'm still you're number one cheerleader.

Richard


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 Post subject: Re: PSG understanding and development overview:
PostPosted: Sun Jul 24, 2011 9:43 am 
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Joined: Tue Apr 19, 2011 10:54 am
Posts: 76
Location: SHOW LOW AZ USA
The weekend fun was setting up the equipment described in my previous post, and giving it a test run using the BEAST as the Unit Under Test (UUT). The basic tests were for the harmonic content of each open string (excited at fret 28) as a function of time (sustain/decay), and the combined open string profile as excited at fret 28 (strum). The all strings at all frets (scrub) is yet to be added.

The “capture” signal path is from the PSG (no VP or effects) into the Hi Z input of the R24 wherein it is recorded, thru to the input of the Real Time Analyzer (RTA) where it is displayed in real time, and from there to the Sonar X1 for further processing. An audio track using one of the built in microphones is used to describe the test activities is also recorded.

The captured signal in the R24 can then be played back using the “metronome” function to define the time line for purposes of quantifying sustain/decay etc.

The FSA/OSCILLOSCOPE software allows viewing and capturing the harmonic content at any instant of time. The change in the relationship of the individual harmonics with time is an input to the definition of tone or timbre. Tone is a dynamic thing on the PSG = constantly changing as the individual harmonics increase and decrease with respect to each other as the whole spectrum decays at the high end.

Another aspect that affects tone are the phase relationship of the harmonics. The phase can be affected by the RLC filtering effect of the standard wound pickups, the location of the pickup, and the picking point of the string…and then there is the effect of preamp settings, and speaker/cabinet introduced changes. Defining tone is a complex and multi faceted thing.

Anyway, the system functions and much can be learned by using it.


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 Post subject: Using the "system"
PostPosted: Mon Jul 25, 2011 2:02 pm 
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Joined: Tue Apr 19, 2011 10:54 am
Posts: 76
Location: SHOW LOW AZ USA
The first serious run using the “system” was to profile the individual open strings (one at a time) allowing about 12 to 16 seconds for the signals to die out. The data (waveforms) were placed on one track, and a verbal description of activities placed on another using one of the R24’s built in microphones.

This was followed by the “strum” of the open strings…excited at fret 28 and allowed about 16 seconds to decay.

Next was the “scrub” which is continually strumming all strings at all frets above the bar, and moving the bar to all frets…no decay time needed in this case.

Then there was the response signal from the pickup for exciting the PSG by hitting various locations with the bar. The locations were front apron center, end plate center, right rear leg center, and rear apron center. No decay time needed here.

These signals were recorded on the R24 without any effects. At the same time they were fed to the computer running the FSA program so that their changing spectrum could be observed. These same signals may be replayed for subsequent processing including harmonic content vs time after excitation. These processed presentations may then be captured as “frames” and converted to jpeg or other formats, and stored (as in Photobucket, and made available to whoever is interested. This allows comparing PSG and pickup combinations from a “library” of data. The dynamics are lost by reducing the presentation to “frames”.

The audio signals may made available in the WAV and other common formats so that those interested can hear, and if they have the FSA software see the harmonic dance that takes place in the data along with the sound.

The “system” components are:
The ZOOM R24 for recording the data.
http://www.samsontech.com/products/prod ... rodID=2054
A computer for processing and viewing.
The TRU RTA FSA and oscilloscope software to view and capture and process the signals.
http://www.trueaudio.com/rta_abt1.htm
The SNAGIT software to reduce the FSA presentation to jpeg or other format “frames”.
http://www.techsmith.com/snagit/
PHOTOBUCKET to store the “frames”.
http://photobucket.com/
Add SONAR X1 for more sophisticated processing.
http://www.cakewalk.com/products/sonar/
Add a VIDCAM to record the activity.

Four runs were made this AM =:
Using one pickup = Danny Shields #1,
Three 14 string PSGs = the BEAST, a PST 13 series, and a Sierra Bill Stafford setup.
The BEAST had the DS#1 used in both the neck and bridge slots.
In all cases the DS#1 was set at the tap giving 16K ohms.

Getting the data takes about 15 minutes per PSG. Post processing is another issue…it depends what info is desired.

This same system can be used to compare bars, sustain vs. bar type and string location, string noise as a function of bar type, string harmonics and sustain vs. age/use etc., and even the spectrum of use by player, both before and after the amp and effects, and then the Sound Power Level at different parts of the room


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 Post subject: Re: PSG understanding and development overview:
PostPosted: Tue Jul 26, 2011 9:46 am 
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Joined: Tue Apr 19, 2011 10:54 am
Posts: 76
Location: SHOW LOW AZ USA
SUSTAIN/DECAY chart example from using the system.

Image

Sustain, as best I can figure from the various threads etc, is the last thing heard as the sound dies out. That “last thing” will depend upon what strings were excited. In our basic example we will use a 14 string instrument (largest frequency range), and excite all open strings at the same time (strum at fret 28), and watch as the frequencies decay. The last frequencies remaining will be the index to what would be called “sustain”. The sample times will be 0,1,2,4 and 8 seconds.

You can see on the chart that the last frequencies for this PSG and pickup combination is around 70 to 140 Hz. By the 8 second mark, all other frequencies have decayed. 70 to 140 Hz is the resonant portion of this PSG + pickup’s spectral response.

This chart is the first of four re the tests mentioned in the previous post = BEAST with DS#1 pickup in the neck position, Beast with DS#1 in the bridge position, PST 13 with DS#1, and Sierra Bill Stafford with DS#1. From these we can compare the results of same pickup in all four situations, same pickup in two locations on the same PSG, sustain and resonant points on different instruments, etc.

From the top trace (time = 0 seconds) it may be seen that the frequencies fall off below 100 Hz, and above 2K Hz. If the PSG was a 10 string E9, the low frequency information would not be available as the low strings are not low enough for the experiment.

It may also be seen how the high frequencies fall of rapidly with time.

When we repeat this experiment with the DiMarzio pickup we will see the amount of difference changing the pickup makes.

The next post will show the meaning of some "test" terms.


Last edited by ed packard on Mon Aug 01, 2011 2:45 pm, edited 1 time in total.

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 Post subject: Re: PSG understanding test terms
PostPosted: Mon Aug 01, 2011 2:44 pm 
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Joined: Tue Apr 19, 2011 10:54 am
Posts: 76
Location: SHOW LOW AZ USA
The basic excitations for these looks at system and component response are pick, strum, and scrub. Pick is one string in most cases…Strum is a rake of all strings at some fret and read at some fret…scrub is a rake of all strings at all frets and read at all frets.

Let’s look at what we can learn with the FSA from a “pick” on a single string. We will use string 14 on the beast = C1 to show the harmonic content of a single vibrating string. We will name the notes associated with the various harmonics. This will help explain why we like the scales we do, and why we like the chords we do. Our music comes from a European and string background.

Image

Along with the vibrations-scale-chord association to be seen, the non damped response of some other strings may be seen at the lower part (floor) of the “pick” frequencies. Some of these can come from sloppy picking, and some from the mechanical coupling of the strings thru the bridge and nut. It should be noticed that this effect is greater for the low strings as the tension is less on them. My BEAST 14th string is the lowest available to show these effects.

Now we move on to the “strum” of the open strings at fret 28. The resulting vibrations are the summation of all open strings and their many harmonics passed thru the pickup. The higher frequency end of the “strum” frequency spectrum decays with time eventually leaving only a portion of the lower part of the spectrum to be heard…this lower frequency signal is what is commonly called “sustain” as it is the last heard after the strings are excited and decay over some amount of time.

Image

Next is “scrub”. Scrub is continually strumming the strings at any/all frets while moving the bar to all frets. The peak signals are captured. This shows the result of a variety of “filters” on the energy entered into the strings by the strums. Filter number one is the vibration of the strings themselves. Filter number two is the energy lost via the mechanical coupling of the strings thru the bridge and nut, or the bar and hand. Filter number three is the energy lost via coupling thru the nut-bridge-bar into the mechanics of the of the changer and body. The string energy that is not reflected by the string terminations is absorbed into the lower parts of the PSG. It will be later shown that those absorbed to stimulate the various parts of the mechanism are those lost in the decay vs. time.

Image

And to show the relationship between pick, strum, and scrub:

Image


We may as well add the chart for delay, and sustain:

Image

The top trace is scrub, the next trace is strum at 0 seconds, and the bottom trace is strum after 8 seconds. This type of format allows a quick comparison of pickups, pickup locations in neck-bridge-or? PSGs, strings, bars, and other variables deemed to affect tone, decay, sustain, et al.

We will use these presentations to compare the DS#1 Pickup in the BEAST neck and bridge positions, the DiMarzio pickup in the BEAST neck and bridge positions, the DS#1 in the PST 13 series 4X5, and the Sierra Bill Stafford model.


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