[sdiy] sync conditioning/simple triangle oscillator without linear voltage control

ulfur hansson ulfurh at gmail.com
Fri Feb 22 17:56:45 CET 2019

hello richie,

I already have constructed an instrument that works quite well, using high
powered class D amplifiers and custom wound electromagnets to induce
feedback in an acoustic set of strings. here is a brief description of my
harp, along with demo recordings;
https://ulfurhansson.com/SEGULHARPA-ELECTROMAGNETIC-HARP (kind of an
acoustic synthesizer/organ?)

the internal circuitry has patchpoints for experimenting with additional
processing/signal conditioning. right now I am using waveshapers to change
timbre/harmonics as you press harder/lighter on the capacitive touch sensor
keyboard on the front panel.

it works great, but i'd still like to explore other avenues for varying
timbre control. I feel my idea of a synced oscillator tethered to each
string is exciting as the sync artifacts will provide a much richer
harmonic response, that is if i can figure out how to implement it with
limited space and solve the challenge of signal conditioning before SYNC

it doesn't have to be perfect, and sync errors as the signal grows stronger
could actually be an interesting addition to the instrument timbre. I would
probably add a VCA to the oscillator output to control the level of output
mixed into the feedback signal depending on how hard you press against the
keyboard (aftertouch).

thank you for your thoughts on this!
all the best,

fös., 22. feb. 2019 kl. 11:43 skrifaði Richie Burnett <
rburnett at richieburnett.co.uk>:

> Synchronising an oscillator to a vibrating guitar string waveform might be
> quite challenging. Different frequencies travel along tensioned strings at
> different speeds leading to a dynamic waveform with likely many
> zero-crossings per cycle. This is particularly so just after plucking where
> string tension is highest and high-frequency partials are loudest.
> Attempts to extract pitch periods from harmonically complex waveforms
> based on zero-crossings are usually of limited success unless you can
> either heavily filter the input waveform to remove harmonics, or use
> something like a PLL that will tend to inherently reject harmonic energy in
> its reference signal if you slug the loop filter enough.
> Are you trying to make something like the e-bow?
> -Richie,
> Sent from my Xperia SP on O2
> ---- ulfur hansson wrote ----
> hello list,
> I need to find a triangle oscillator design that meets two requirements;
> 1 - it needs to have a sync input that can sync to a signal of varying
> amplitude ( it is actually a single guitar string)
> 2 - it has to be tiny! I plan to design it using 0805 caps/resistors and
> SOT transistors etc...
> they idea is to use this oscillator to reinforce a feedbacking signal
> induced in the string using electromagnetic pickups and actuators. I have
> already constructed an instrument that works great, but I'd like to use
> this addtional circuitry to accentuate different harmonics of the resulting
> tone by mixing the synced oscillator in with the feedbacking string signal.
> since the sync input signal is not a steady pure waveform,i will probably
> need to do some signal conditioning - any ideas regarding comparator
> designs for converting varying amplitude signal to steady square wave would
> be greatly appreciated! perhaps a simple diode compressor would be helpful
> too...
> I hope this topic doesn't come across as too nebulous, but really any
> ideas or helpful thoughts comments would be greatly appreciated!!
> all the best,
> -úlfur
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