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<div class="moz-cite-prefix">This issue has been tread a lot in the
realm of guitar "octavers", mainly octave down effects, and guitar
synthesizers. The most popular circuit for guitar octavers seems
to be the peak detector circuits rather than zero crossing
detection. Google the schematic for the Boss OC-2 for that
type. Some guitar synthesizers like Roland's GR-300 used zero
crossing detection, but had separate processing per string which
makes the job easier since you only need good tracking for ~2
octaves. They also used filters that would switch center
frequency based on the detected pitch.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">The OC-2 method is certainly more
economical circuitry-wise. I've been curious lately about the
history of that variable threshold detector. Earliest use I could
find seems to be the ElectroHarmonix Octave Multiplexer from the
seventies, but couldn't find any patents related to it. Anyone
know of earlier instances of the same or similar circuits?</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">úlfur, beautiful looking instrument,
BTW.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Dave<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 2/22/19 8:56 AM, ulfur hansson
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAG9O7x0WZUXBvMbrMVejqCjGOJc7t0z+9euo6-L+Gwmu5ppi2w@mail.gmail.com">
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<div dir="ltr">
<div dir="ltr">hello richie,
<div><br>
</div>
<div>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; <a
href="https://ulfurhansson.com/SEGULHARPA-ELECTROMAGNETIC-HARP"
moz-do-not-send="true">https://ulfurhansson.com/SEGULHARPA-ELECTROMAGNETIC-HARP</a> (kind
of an acoustic synthesizer/organ?)</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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 input.</div>
<div><br>
</div>
<div>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).</div>
<div><br>
</div>
<div>thank you for your thoughts on this!</div>
<div>all the best,</div>
<div>-úlfur</div>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">fös., 22. feb. 2019 kl. 11:43
skrifaði Richie Burnett <<a
href="mailto:rburnett@richieburnett.co.uk"
moz-do-not-send="true">rburnett@richieburnett.co.uk</a>>:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">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.<br>
<br>
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.<br>
<br>
Are you trying to make something like the e-bow?<br>
<br>
-Richie,<br>
<br>
Sent from my Xperia SP on O2<br>
<br>
---- ulfur hansson wrote ----<br>
<br>
<div dir="ltr">hello list,
<div><br>
</div>
<div>I need to find a triangle oscillator design that meets
two requirements; </div>
<div><br>
</div>
<div>1 - it needs to have a sync input that can sync to a
signal of varying amplitude ( it is actually a single
guitar string)</div>
<div><br>
</div>
<div>2 - it has to be tiny! I plan to design it using 0805
caps/resistors and SOT transistors etc...</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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...</div>
<div><br>
</div>
<div>I hope this topic doesn't come across as too nebulous,
but really any ideas or helpful thoughts comments would be
greatly appreciated!!</div>
<div><br>
</div>
<div>all the best,</div>
<div>-úlfur</div>
<div><br>
</div>
</div>
</blockquote>
</div>
<br>
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</blockquote>
<p><br>
</p>
<pre class="moz-signature" cols="72">--
David Moylan
Expedition Electronics
sonic adventures!</pre>
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