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Re: Slide guitar - acoustics question
Right, the slide acts as a string shortener as does a fret, not as a
damper. This neat trick sets both sides of the damper vibrating, then the
slide simultaneously lengthens one side of the vibrating string while
shortening the other.
On Mar 22 2007, Cornelia Fales wrote:
Thanks, Martin - we thought of that, except that it has something to do
with the slide(r) itself, since we tried it sliding the finger instead
of the slide(er), and neither our ears nor the spectrograph indicated a
Martin Braun wrote:
Dear Nina and List,
by damping (touching) a vibrating string in the middle of its length
you get two vibrating half-strings.
Now if you slide the damping finger, one half get shorter producing a
rising gliss and the other half gets longer producing a falling gliss.
The falling gliss is much softer, because a string section that gets
longer increases in mass and thus dramatically decreases in vibration
You might like to have your students find the solutions themselves by
various double damping experiments.
Neuroscience of Music
S-671 95 Klässbol
web site: http://w1.570.telia.com/~u57011259/index.htm
----- Original Message ----- From: "Cornelia Fales" <cfales@xxxxxxxxxxx>
Sent: Wednesday, March 21, 2007 11:14 PM
Subject: Slide guitar - acoustics question
Can anyone explain this slide guitar technique?
1) Lightly damp a single guitar string at, say, half its length to
get the harmonic pitch an octave above the open string pitch (ie,
interfering with the fundamental and odd modes of vibration),
2) Replace your damping finger with a steel slide at the same damping
pressure, and slide it up the neck to some point along the neck.
The result is the expected ascending glissando from the beginning
harmonic pitch to the pitch at the end of the glide, but also a
fainter descending glissando that moves at the same speed and
distance as the stronger ascending glissando. The downward glissando
is easily audible with practice - more so if the rising harmonics are
filtered out - and is also clearly visible on a spectrogram.
My students and their teacher have two questions: 1) if the slide
really maintains the same pressure as the original damping finger,
then theoretically its movement doesn't change the length of the
string or the fundamental, but must instead be interfering with
different vibration modes as it slides upward. So how does it
produce a (chromatic) glissando?
2) what accounts for the descending glissando?
Thanks for any insights.
Anthony J Watkins
Department of Psychology,
School of Psychology and Clinical Language Sciences,
The University of Reading, Reading, RG6 6AL, UK.
phone: +44 (0)118-378-7559; fax: +44 (0)118-378-6715
home page: http://www.personal.rdg.ac.uk/~syswatkn/home.html