[sdiy] Timbral musings

[Czech Martin]

I play electric guitar myself and
I noticed that strings tend to synchronize,
i.e. they exchange some energy so that
not to much "phasing" will appear.

There is still some motion in it, but less then one
could expect for perfectly "isolated" strings.

It is not similar but perhaps an analogy to soft sync
(unwanted) when oscillators are not properly isolated
from each other.

If you have a "whammy bar" or "vibrato bar" on your
guitar there will be some "pitch envelope"
if you slam the strings very hard (that's
what I often do). The perception is that the pitch
is a bit lower initially and will raise to normal
when the string has come to lower amplitude.
Of course this depends also on the guitar head,
I mean if you have a solid locking mechanism or a 
carbon type slide bearing (which is what I prefer).

Depending on the frets and your playing style
the notes will be more or less out of tune,
also depending where they are played on the fret board.

The thick strings (E A D) will sound a bit too high 
if they are fretted high, because they come closer
to the pickup magnet. Depends on the construction.

I think most of the time the tuning of a keyboard
instrument is much different from a guitar.
Octaves are octaves, but the rest may differ very much.


I had a discussion with an engineer (colleague) recently,
this guy would'nt believe that tubes still rule 
for guitar heads. I tried to tell him that it is not only tubes,
but also transformer, cabinet and speaker issues and
that at least I have no clue how to determine or to model the nonlinear
system parameters of that signal chain.
I have never seen a reasonable publication on that.
Most transistor or DSP representations of guitar amps
sound like crap, but I must admit that no big effort seem
to have been spend in emulating that better.
 
m.c.

-----Original Message-----
From: jhaible at debitel.net [mailto:jhaible at debitel.net]
Sent: Dienstag, 18. Februar 2003 14:26
To: harrybissell
Cc: stromeko at compuserve.de; synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Timbral musings


Well I agree with most of what you said (the various tunings of
various guitarists being a different matter).

 - "Semi" true:
Well I try to be more clear this time.
If you play a fifth on two guitar stings, the fundamental of
both is not exactly in an integer ratio.
So without waveshaping (distortion), you get beating, which is
more or less just amplitude modulation at a sub audio frequency.
Now *with* waveshaping, this sub audio component will change how
the input signal drives the nonlinearity, thus producing 
a timbre modulation at the same rate as the beat frequency.
D'accord?

- Strings being bars:
Right. 
And even with _very_ stiff objects oscillating it can be fun to 
run the resulting waves thru heavy distortion.
I tried my Wurlitzer EP200A thru a Big Muff a few days ago.
I wouldn't have believed it (a friend suggested to try it), but
it sounds _wonderful_ with a lot of distortion.
Bass notes - an awsome rich sustaining sound (until it dies away;
then it's quite unbearable without noise gate).
And power chords (no 3rds) are as nice as on a guitar.

JH.




Zitat von harrybissell <harrybissell at prodigy.net>:

> jhaible wrote: <snip>
> 
> > Yes, and this intermodulation sounds great if the fouths or fifths are not
> > perfectly pure: Some of the intermodulation products are in the sub audio
> > range, and they act like a LFO modulation of the waveshaper function ...
> 
> This is semi true. On a guitar they are equally tempered...and as the
> interval
> of fifth and fourth are inverse (meaning a fifth up is a fourth down...) the
> detuning is the same.
> 
> OTOH guitar strings are considerably non-harmonic... the overtone series is
> quite sharp (maybe they should be called guitar-bars rather than strings...
> but
> then
> all the guitarists would like to go there to get drunk...  ;^)
> 
> These sharp harmonics make the IM products pretty obnoxious. Moral... don't
> waveshape polyphonic guitar unless you do it on each sting separately... or
> if
> you
> use a global waveshaper, stick to octaves, fourths and fifths. If not you
> get
> pure mud
> (which some may argue they want...)
> 
> Guitar (equal tempered) thirds usually do not work through a waveshaper
> (clipper)
> at all...
> 
> (this info relates to Guitar as sound source... with VCOs you could make
> pure
> thirds...)
> 
> H^) harry
> 
> >
> >
> > > >Another overdrive trick that might work with some waveshapers as well
> > > >is to start with a harmonically rich waveform that still has a strong
> > > >fundamental. As you drive it, it actually sounds cleaner as it
> > > >approaches a square wave.
> >
> > And if you drive a soft clipping VCF (or VCA) with saw waves, these
> > are rounded and loose some of their upper harmonics, too. That's
> > why some filters sound "fatter" that others, even if their small signal
> > behaviour (poles ...) is identical.
> >
> > JH.
> 
> 
> 

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