PV-1 Pitch to Voltage update - Guitar working...

[Harry Bissell]

I've been experimenting all weekend, and have gotten the guitar to work
pretty well with the PV-1.  I built a pitch extractor that gives good
tracking. When I'm done I'll post the schematics... Probably no PCB for
this one due to possible patent infringment, although I need a legal
opinion since the company that holds the patent is long time defunct. It
should still be possible for persons to build their own for their own
use. I could make the "artwork" available though.

The pitch extractor was a real pain in the @ss to get working... It
relies on two comparators that cannot have any hysteresis... etc. After
fighting LM311's all day...
I decided to use an op-amp as a comparator that just WILL NOT
oscillate...

The (ta-da)  LM741C. Who says it doesn't have its place....

I tried vocals in the pitch extractor... It worked a lot better than
previously reported... but still I won't be doing any concerts soon...
even with a dog-collar mic... The main problem is that the microphone
picks up a lot of sound from the amp. Maybe if you use headphones and
record...OK. It WAS really wierd when I pitch shifted the oscillator up
a couple of octaves... It was still noticibly my voice (the vibrato...
cracking...etc...) but
not in any range I've been able to hit since the testoserone kicked in
in the seventh grade...

Vocals could work... but I haven't come up with a way to latch the note
properly at the end... There is a patent (BobMoog... see Don Till's site
for detail) that uses a second sample and hold and updates the second
one only when the pitch is within a range of the  first sample/hold. I
have a similar system in my 360 Systems "Slavedriver" which uses a
voltage controlled slew limiter... When the Amplitude is high... I track
fast... as amplitude drops I increase the lag time... until it "holds"
forever.

I'm working on the note detect logic next... I guess I'll be doing a hex
guitar synth soon...
The note logic will be needed to make sure that a valid sample stays in
the synth after the guitar decay....

BTW... someone suggested that the Roland Guitar Synth (original CV
unit...) was the "best tracking" guitar synth of all time because of the
adaptive filters... It looks like this might just be true... If you
filter hard enough to guarantee that the open string will track without
skipping octaves... the 12th fret has very little sustain.... If you
make the 12 fret work good... the the open string will skip if you are
careless where you pick the string....
(if you pick at 1/2 the string length... you are almost guaranteed to
not have second harmonic skipping... it becomes an anti-node...) Of
course I'm not at all careful so....

The PCB's are ready. I'll pick them up andsend them to TomG tomorrow (or
possibly Tuesday at the latest...).

H^)   harry