50kHz pitch shifter

[Harry Bissell]

I suggested a sampling o'scope... some are capable of 10Msamples/second.  Then
massage the data (in non-real time) and play it back. Sound card will not cut
it, as you noted.

Scott Gravenhorst wrote:

> <yet more smoke blowing>
> I thought about sample slow down, but Tony didn't indicate
> the band the signal occupies other than there is some semblance of
> a sine wave at 50 kHz.  Sampling a signal whose passband is in this
> same neighborhood or even higher with a soundblaster type card
> would be worthless since it's upper sample rate is only 44kHz and
> change.  Indeed, my guess is that if a sine is recognized on a scope,
> more likely the signal "impressed" upon it may be quite a
> bit higher.  Audio tape techniques will be quite useless at this
> pass band as well, since audio pretty much tops out around 25kHz,
> most audio tape systems have limitations here.
>
> The key to me is:  Is it modulated or mixed, and if modulated, how?
> Freq, amp or phase.
>
> Tony also didn't say how much time and $$ are available for this.
> Sample slow down could be valuable if the sampler is capable of
> really high rates and can also be rate adjusted for playback.
> </yet more smoke blowing>
>
> Harry Bissell <harrybissell at prodigy.net> wrote:
> >My 2/100ths
> >
> >I don't think the ring mod / pitch shifter is the way to go. The "noise"
> >not have all
> >harmonics shifted the same ratio, it will be the same fixed anount. If
> >the noise had
> >any intelligence it will be lost.
> >
> >Is the noise "noise" re: unwanted signal on the 50KHz, or some artifact
> >???
> >
> >I'd get a good sampling o'scope (physics dept SHOULD have one...) and try
> >to output
> >the data as a file (some PC format...) Then try to convert that to a .wav
> >file and clock it
> >bask at reduced frequencies... like slowing down a tape...
> >
> >Or run a tape recorder at 30ips and play back at 3 1/4" or so...
> >
> >H^) Harry
> >
> >Scott Gravenhorst wrote:
> >
> >> <smoke blowing>
> >> Hmm.  I guess alot depends on the band on which the noise exists
> >> and how the "intelligence" bacame modulated on it.
> >>
> >> If the intelligence is simply mixed with the 50kHz sine, the
> >> carrier can be stripped off with a notch filter.
> >>
> >> The sine wave, if constant, would be uninteresting, but the noise
> >> and other perturbations present might be.  If the noise and other
> >> signals are already in the audio range and are amplitude modulated
> >> on the 50 kHz sine, a high-Q notch filter tuned to 50 kHz might work.
> >> There's more trouble, I think, if the carrier is not very stable.
> >> A wider notch might work.  Again, much depends on the band where
> >> the desired signal sits.
> >>
> >> If the desired signals are frequency modulating the sine, the
> >> "intelligence" can be recovered perhaps using a phase locked loop
> >> locking to the 50kHz sine, then listening to the VCO's control
> >> voltage.
> >>
> >> Once recovered, If the noise is in a band above human hearing, then
> >> indeed, you will need a shifter of one kind or another.  A pitch
> >> shifter will preserve harmonic relationships, a frequency shifter
> >> will not, but rather the hertz differences.  (that may not be a
> >> precise definition and I'm sure that it will be tweaked by others
> >> if it's not).  It may be interesting to "hear" this using both
> >> approaches.  It may be possible to use digital methods to stretch
> >> the signal out in time, like sampling it at one rate and playing back
> >> at another.  That's a whole other can of worms and again, alot
> >> depends on the frequency band of the intelligence signal.
> >>
> >> I think the ring mod approach might also work, then followed by
> >> a notch filter to strip the sine wave.  But this method provides
> >> no demodulation that I'm aware of, just shifting the whole mess.
> >>
> >> Anyway, I'd say what you're attempting sounds very interesting.
> >> </smoke blowing>
> >>
> >> Toby Paddock <tpaddock at seanet.com> wrote:
> >> >Hello,
> >> >A friend is doing a physics experiment for school and
> >> >one of the resulting signals is a 50kHz sine wave with
> >> >noise on it. The noise and ringing is one indication
> >> >of what is going on. We thought it might be worth
> >> >bonus points to be able to listen to it.
> >> >So we need a pitch shifter or divider.
> >> >
> >> >Maybe a 1/100 divider. Sample one cycle and play it
> >> >back slow and do it again. Sync could be direct from
> >> >the clean sine source. The wave is periodic and fairly
> >> >repetitive, cycle to cycle. But the sample rate would
> >> >be pretty high.
> >> >
> >> >Maybe a ring mod (my favorite). Assuming the carrier
> >> >is a clean sine wave would the output have the same
> >> >waveform as the input. It would not need to be perfect
> >> >as long as you could hear the change. Any tips on
> >> >what ring mods like 50kHz inputs?
> >> >I have a sample AD633, but have never built a ring mod.
> >> >
> >> >Ideas?
> >> >
> >> >Thanks,
> >> > - -- -  Toby Paddock
> >> >
> >> >
> >>
> >> -- Scott Gravenhorst
> >> -- Linux Rex, Linux Vobiscum  |  RedWebMail by RedStarWare
> >> -- FatMan: www.teklab.com/~chordman
> >> -- NonFatMan: members.xoom.com/_XMCM/chordman/index.html
> >> -- The 21st century does NOT start in the year 2000!!!
> >
> >
>
> -- Scott Gravenhorst
> -- Linux Rex, Linux Vobiscum  |  RedWebMail by RedStarWare
> -- FatMan: www.teklab.com/~chordman
> -- NonFatMan: members.xoom.com/_XMCM/chordman/index.html
> -- The 21st century does NOT start in the year 2000!!!