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<div class="moz-cite-prefix">The halfwave rectifiers are used to
track the peak positive and negative levels of the input
waveform. Those levels are used as a variable threshold for the
comparators which trigger the flip flop. See the connection from
R10/R32 node into both comparators. Without adaptive filtering
this method seems to work better than zero crossing detection.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Korg used an even more economical
version where they only track the positive peak and hold the
negative threshold at ground (well, at pseudo-ground for a single
supply):</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><a class="moz-txt-link-freetext" href="https://www.experimentalistsanonymous.com/diy/Schematics/Vibrato%20and%20Pitch%20Shift/Korg%20OCT-1.gif">https://www.experimentalistsanonymous.com/diy/Schematics/Vibrato%20and%20Pitch%20Shift/Korg%20OCT-1.gif</a></div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I've never done an A/B to see if there
are any tracking differences.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">The phase of the flip-flop does matter
because it controls where in the cycle the inversion takes place.
Valve Wizard discusses it here:
<a class="moz-txt-link-freetext" href="https://www.valvewizard.co.uk/uboat.html">https://www.valvewizard.co.uk/uboat.html</a> <br>
</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">On 10/9/24 1:25 AM, Tom Wiltshire
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:4B0DDB3B-BE4F-425F-B559-1764B49C908A@electricdruid.net">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
IC2 and IC3 are halfwave rectifiers providing set and reset signal
to the flip-flop. There's some detail here that I feel like I'm
forgetting - does the flip-flop have to be 90 degrees out of phase
for some reason? I can't remember.
<div class=""><br class="">
<div class="">Then those flip-flop signals feed the FETs that
provide the invert/noninvert action on the amplifiers both
built around op-amps in IC5.
<div class=""><br class="">
</div>
<div class="">Tom<br class="">
<div><br class="">
<blockquote type="cite" class="">
<div class="">On 8 Oct 2024, at 22:58, Sean Ellis <<a
href="mailto:tensiontype@hotmail.com"
class="moz-txt-link-freetext" moz-do-not-send="true">tensiontype@hotmail.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="elementToProof"
style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;">Here's
the schematic, wondering what the diodes might be
doing here?</div>
<div class="elementToProof"
style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;"><br
class="">
</div>
<div class="elementToProof"
style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;"><a
href="https://www.hobby-hour.com/electronics/s/oc2-octave.php"
id="LPlnk583876" class="moz-txt-link-freetext"
moz-do-not-send="true">https://www.hobby-hour.com/electronics/s/oc2-octave.php</a></div>
<div class="elementToProof"
style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;"><br
class="">
</div>
<div class="elementToProof"
style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;">There's
a few nice videos showing it's sound on youtube.</div>
<div
style="font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-family: Calibri, Helvetica, sans-serif; font-size: 12pt;"
class=""><br class="">
</div>
<hr
style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; display: inline-block; width: 802.609375px;"
class=""><span
style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;"
class=""></span>
<div id="divRplyFwdMsg" dir="ltr"
style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"
class=""><span
style="font-family: Calibri, sans-serif; font-size: 11pt;" class=""><b
class="">From:</b> Synth-diy <<a
href="mailto:synth-diy-bounces@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">synth-diy-bounces@synth-diy.org</a>>
on behalf of Harry Bissell <<a
href="mailto:hbissell@wowway.com"
class="moz-txt-link-freetext"
moz-do-not-send="true">hbissell@wowway.com</a>><br
class="">
<b class="">Sent:</b> Tuesday, 8 October 2024
10:41 PM<br class="">
<b class="">To:</b> Tom Wiltshire <<a
href="mailto:tom@electricdruid.net"
class="moz-txt-link-freetext"
moz-do-not-send="true">tom@electricdruid.net</a>><br
class="">
<b class="">Cc:</b> <a
href="mailto:synth-diy@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">synth-diy@synth-diy.org</a><span
class="Apple-converted-space"> </span><<a
href="mailto:synth-diy@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">synth-diy@synth-diy.org</a>><br
class="">
<b class="">Subject:</b> Re: [sdiy] Boss Octave -
was Re: Frequency shifted from BBD?</span>
<div class=""> </div>
</div>
<div
style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; font-size: 11pt;"
class="">By doing it by switching polarity they
avoid the problems of envelope following ( one of my
pet peeves, if you recall… :^) and also eliminate
the need for an OTA etc. I had not thought of this
as a “ring mod” before, it’s an interesting way to
view it.<br class="">
Mr & Mrs Account<br class="">
<br class="">
> On Oct 8, 2024, at 2:48 PM, Tom Wiltshire <<a
href="mailto:tom@electricdruid.net"
class="moz-txt-link-freetext"
moz-do-not-send="true">tom@electricdruid.net</a>>
wrote:<br class="">
><br class="">
> Yes, that's true. I hadn't thought of it that
way, but that's exactly what it's doing. It's
essentially a multiplication between the input
signal and a siganl that goes "+1, -1, +1, -1,+1,-1,
etc" - so, yeah, ring mod.<br class="">
><br class="">
> No wonder they still have a low pass filter
after it! Although you gain some "responsive"
qualities, you're also going to get a ton of extra
stuff you don't need harmonically. Nonetheless, the
dynamics are good. As Benjamin said, about the only
other way to do that would be to re-impose them
using a compander chip or similar, like the Paia
Roctave unit does. That's exactly the other
approach, iirc. It uses the constant-amplitude
squarewaves, bur then uses the envelope of the
original signal to impose the original dynamics on
them.<br class="">
><br class="">
> Tom<br class="">
><br class="">
>> On 8 Oct 2024, at 11:54, Roman Sowa via
Synth-diy <<a
href="mailto:synth-diy@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">synth-diy@synth-diy.org</a>>
wrote:<br class="">
>><br class="">
>> Which is basicaly amplitude modulation with
supressed carier, or as synth nerds like to call it
- ringmodulation. Input is modulated with square
wave of half frequency, so the resulting spectrum
contains sums and differences of the previously
filtered input and square wave spectrum. Upper part
can be filtered, and we get shifted down by half
fundamental frequency output.<br class="">
>><br class="">
>> Roman<br class="">
>><br class="">
>> W dniu 2024-10-08 o 12:31, Tom Wiltshire
pisze:<br class="">
>>> There's actually one further twist to
this. The flip-flop signals are not used directly,
but instead used to switch between non-inverted and
inverted versions of the input wave. The effect of
flipping every other input wavecycle is to produce a
new waveform with the fundemental an octave lower.
The advantage over using the square directly is that
the resulting output changes with changes in the
input in a way that the square wave doesn't. This
makes the pedal seem more "responsive", since it's
not just blasting you with a constant volume square
wave all the time - instead the dynamics and
harmonics of the octave-down signal can both change.<br
class="">
>>> Tom<br class="">
>>>> On 8 Oct 2024, at 08:20, brianw
<<a href="mailto:brianw@audiobanshee.com"
class="moz-txt-link-freetext"
moz-do-not-send="true">brianw@audiobanshee.com</a>>
wrote:<br class="">
>>>><br class="">
>>>> The Boss Octave does not actually
shift pitch. The algorithm is completely different.<br
class="">
>>>><br class="">
>>>><br class="">
>>>> The analog signal is boosted to the
point of extreme clipping, making it effectively a
square wave. There's some EQ ahead of this to favor
the fundamental rather than the harmonics, but
you've probably noticed that harmonics can still
slip through. Once the input signal is clipped to a
square wave, it is processed with CMOS gates to cut
the frequency in half, and the again to one quarter.
These represent one octave down and two octaves
down. Each of those are square waves, too, so
they're processed with a low-pass filter to remove
(redundant) harmonics. Finally, the original input
is mixed with the one-octave down and two-octave
down signals. Voila!<br class="">
>>>><br class="">
>>>> The Boss Octave technique cannot
produce any interval other than one octave down (and
two octaves down by repeating part of the process).<br
class="">
>>>><br class="">
>>>> FYI, the digital gate that can drop
a square wave by one octave is very simple and
cheap, and often there is more than one in the same
chip. Thus, the two octaves down signal is
practically free.<br class="">
>>>><br class="">
>>>> Brian<br class="">
>>>><br class="">
>>>> p.s. I made a decent recreation of
this in software until I realized that Logic Studio
Pro already has such a plugin that works better than
mine.<br class="">
>>>><br class="">
>>>><br class="">
>>>>> On Oct 7, 2024, at 9:49 AM,
Didier Leplae <<a
href="mailto:didierleplae@yahoo.com"
class="moz-txt-link-freetext"
moz-do-not-send="true">didierleplae@yahoo.com</a>>
wrote:<br class="">
>>>>>> Thanks for all the replies
to this question! It’s all very interesting. I used
to have a Boss Octave pedal back in the 80s. I
wonder if it also worked with BBDs.<br class="">
>>>>><br class="">
>>>>><br class="">
>>>>>
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class="">From:</b> Synth-diy <<a
href="mailto:synth-diy-bounces@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">synth-diy-bounces@synth-diy.org</a>>
on behalf of Harry Bissell <<a
href="mailto:hbissell@wowway.com"
class="moz-txt-link-freetext"
moz-do-not-send="true">hbissell@wowway.com</a>><br
class="">
<b class="">Sent:</b> Tuesday, 8 October 2024
10:41 PM<br class="">
<b class="">To:</b> Tom Wiltshire <<a
href="mailto:tom@electricdruid.net"
class="moz-txt-link-freetext"
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<b class="">Cc:</b> <a
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<b class="">Subject:</b> Re: [sdiy] Boss Octave -
was Re: Frequency shifted from BBD?</span>
<div class=""> </div>
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class="">By doing it by switching polarity they
avoid the problems of envelope following ( one of my
pet peeves, if you recall… :^) and also eliminate
the need for an OTA etc. I had not thought of this
as a “ring mod” before, it’s an interesting way to
view it.<br class="">
Mr & Mrs Account<br class="">
<br class="">
> On Oct 8, 2024, at 2:48 PM, Tom Wiltshire <<a
href="mailto:tom@electricdruid.net"
class="moz-txt-link-freetext"
moz-do-not-send="true">tom@electricdruid.net</a>>
wrote:<br class="">
><br class="">
> Yes, that's true. I hadn't thought of it that
way, but that's exactly what it's doing. It's
essentially a multiplication between the input
signal and a siganl that goes "+1, -1, +1, -1,+1,-1,
etc" - so, yeah, ring mod.<br class="">
><br class="">
> No wonder they still have a low pass filter
after it! Although you gain some "responsive"
qualities, you're also going to get a ton of extra
stuff you don't need harmonically. Nonetheless, the
dynamics are good. As Benjamin said, about the only
other way to do that would be to re-impose them
using a compander chip or similar, like the Paia
Roctave unit does. That's exactly the other
approach, iirc. It uses the constant-amplitude
squarewaves, bur then uses the envelope of the
original signal to impose the original dynamics on
them.<br class="">
><br class="">
> Tom<br class="">
><br class="">
>> On 8 Oct 2024, at 11:54, Roman Sowa via
Synth-diy <<a
href="mailto:synth-diy@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">synth-diy@synth-diy.org</a>>
wrote:<br class="">
>><br class="">
>> Which is basicaly amplitude modulation with
supressed carier, or as synth nerds like to call it
- ringmodulation. Input is modulated with square
wave of half frequency, so the resulting spectrum
contains sums and differences of the previously
filtered input and square wave spectrum. Upper part
can be filtered, and we get shifted down by half
fundamental frequency output.<br class="">
>><br class="">
>> Roman<br class="">
>><br class="">
>> W dniu 2024-10-08 o 12:31, Tom Wiltshire
pisze:<br class="">
>>> There's actually one further twist to
this. The flip-flop signals are not used directly,
but instead used to switch between non-inverted and
inverted versions of the input wave. The effect of
flipping every other input wavecycle is to produce a
new waveform with the fundemental an octave lower.
The advantage over using the square directly is that
the resulting output changes with changes in the
input in a way that the square wave doesn't. This
makes the pedal seem more "responsive", since it's
not just blasting you with a constant volume square
wave all the time - instead the dynamics and
harmonics of the octave-down signal can both change.<br
class="">
>>> Tom<br class="">
>>>> On 8 Oct 2024, at 08:20, brianw
<<a href="mailto:brianw@audiobanshee.com"
class="moz-txt-link-freetext"
moz-do-not-send="true">brianw@audiobanshee.com</a>>
wrote:<br class="">
>>>><br class="">
>>>> The Boss Octave does not actually
shift pitch. The algorithm is completely different.<br
class="">
>>>><br class="">
>>>><br class="">
>>>> The analog signal is boosted to the
point of extreme clipping, making it effectively a
square wave. There's some EQ ahead of this to favor
the fundamental rather than the harmonics, but
you've probably noticed that harmonics can still
slip through. Once the input signal is clipped to a
square wave, it is processed with CMOS gates to cut
the frequency in half, and the again to one quarter.
These represent one octave down and two octaves
down. Each of those are square waves, too, so
they're processed with a low-pass filter to remove
(redundant) harmonics. Finally, the original input
is mixed with the one-octave down and two-octave
down signals. Voila!<br class="">
>>>><br class="">
>>>> The Boss Octave technique cannot
produce any interval other than one octave down (and
two octaves down by repeating part of the process).<br
class="">
>>>><br class="">
>>>> FYI, the digital gate that can drop
a square wave by one octave is very simple and
cheap, and often there is more than one in the same
chip. Thus, the two octaves down signal is
practically free.<br class="">
>>>><br class="">
>>>> Brian<br class="">
>>>><br class="">
>>>> p.s. I made a decent recreation of
this in software until I realized that Logic Studio
Pro already has such a plugin that works better than
mine.<br class="">
>>>><br class="">
>>>><br class="">
>>>>> On Oct 7, 2024, at 9:49 AM,
Didier Leplae <<a
href="mailto:didierleplae@yahoo.com"
class="moz-txt-link-freetext"
moz-do-not-send="true">didierleplae@yahoo.com</a>>
wrote:<br class="">
>>>>>> Thanks for all the replies
to this question! It’s all very interesting. I used
to have a Boss Octave pedal back in the 80s. I
wonder if it also worked with BBDs.<br class="">
>>>>><br class="">
>>>>><br class="">
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moz-do-not-send="true">https://apac01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsynth-diy.org%2Fmailman%2Flistinfo%2Fsynth-diy&data=05%7C02%7C%7C658d7df83b004be7b48f08dce7dab8b8%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638640173814403273%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=vPeFQnl79kVAH86u%2Bzet509g%2F7YmsmSX3%2BiQHVdOx2Q%3D&reserved=0</a><br
class="">
Selling or trading? Use<span
class="Apple-converted-space"> </span><a
href="mailto:marketplace@synth-diy.org"
class="moz-txt-link-freetext"
moz-do-not-send="true">marketplace@synth-diy.org</a></div>
</div>
</blockquote>
</div>
<br class="">
</div>
</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
<pre wrap="" class="moz-quote-pre">________________________________________________________
This is the Synth-diy mailing list
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Selling or trading? Use <a class="moz-txt-link-abbreviated" href="mailto:marketplace@synth-diy.org">marketplace@synth-diy.org</a>
</pre>
</blockquote>
<p><br>
</p>
<pre class="moz-signature" cols="72">--
David Moylan
Expedition Electronics
sonic adventures!</pre>
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