50kHz pitch shifter

[Scott Gravenhorst]

<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!!!