ed packard
From:
Show Low AZ
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Posted 1 Dec 2010 9:06 am |
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I had started down the trail of expanding the 1906 32 PSG analysis work done at Jim P's shop to include recorded audio comparisons of several PSGs in Frequency Spectrum Analyzer form (graphs) showing harmonic content at various frets and times after excitation, and using various bars. Rusty R then started his Comparison project, so I will hold my work till after the Nashville PSG shootout.
However, Is there an interest in bar comparison on a single PSG (Sierra Session Series, PST model)?
The bars at hand are the Zircs (7/8", and 15/16"), the BJS Chromed Steel (1").
The FSA results would illuminate differences due to weight, material, smoothness, pressure, scraping vibrato, rolling vibrato, no vibrato, etc.
No volume pedal, 1 meg+ input impedance via M-Audio interface, recorded repeatable data, basic E9 tuning but no mid D etc., separate out wound and not wound strings. Any interest? |
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ed packard
From:
Show Low AZ
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Posted 17 Dec 2010 9:40 am more string vibrations
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We have taken a quick look at the PSG body and mechanical structure. These are mechanical filters
that are to a degree controllable by construction/material issues.
\We have taken a quick look at The common magnetic pickup structures, and how they intercept the
string vibrations; these also become filters choosing which parts of the string vibration they will emphasize.
Next is the actual string vibrational patterns (above) shown in only one dimension…remember that the
string also rotates, and the individual loops and nulls also gyrate about the string.
When a string is excited, the “fundamental” (lowest frequency) is determined by the “Scale Length”, the
String Gauge, the Tension on, and the Material of the string.
The frequencies of our preferred chord and scale notes are also in the string’s vibration pattern. Only
vibrations that have nodes at the bridge and bar are allowed to exist. These can be seen as having odd
and even loops and nodes. The fundamental has an odd number of loops and an even number of nodes.
The next higher frequency of vibration (happening at the same time) has an even number of loops, and
an odd number of nodes…and so forth. In order of appearance, these are fundamental = 1Xf, first
octave= 2Xf, 3Xf, 4Xf, 5Xf, 6Xf, 7Xf, 8Xf, 9Xf, 10Xf, etc. All evens nulls at one half the scale length
(12th fret for open string), so 1,2,4,8,16 X the fundamental will have the same note name as the
fundamental, 3X, 6X, 12X, 24X will all have the same note name as the 3X or 3Xf, 5X, 10X, 20 X will
have the same note names as the 5Xf. And so forth.
If the fundamental (1Xf) gives a C note, then the 1X, 2X, 3X will be C, C, G, C, E, G, B, C, D, E, F, G, A,
And therein we have the notes for two octaves of the C major scale, AND the first 6 notes are those of
the C chord, etc.
In terms of one octave intervals, these notes become 1, 1, 5, 1, 3, 5, 7, 1, 2, 3, 4, 5, 6, intervals.
In terms of two octave intervals, these notes become 1, 1, 5, 1, 3, 5, 7, 1, 9, b11, b12, 13, intervals.
Forget for the moment that the b11 is also a ##9, and the b12 is also a ##11 and a bb13, etc.
Looking at the chart above we can see where the loops and nulls for these occur on the scale length.
Pick the string at the middle of the scale length, and that loop becomes a null, so you have minimized
the ocatave, and reduced any other frequency that does not have a null there.
Touch the center of the scale while or after picking the string, and you will have caused a “harmonic”
‘Sound = chime, or finger harmonic.
These last two principles may be used at other portions of the scale length to control the harmonics
‘o the string(s).
Control the direction and rate of string rotation by how and where you pick and you can control the
amount of harmonic modulation (liveliness) in the signal.
As you can see from the above, the vibrating string is also a filter. Understanding the mechanics of the
vibrating string, and that of the pickup structure and location is key to understanding “tone”, attack,
and sustain. Add to this the filter of the pickup’ RLC and Z, and the sound begins to take shape. |
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