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# Robert Scott

> Just get a hold of any shortwave receiver with BFO capability and have
> a listen.  Go to the 40m or 20m ham bands and tune in a voice station
> "properly".  Then tune in the direction that makes the pitch of the
> voice sound lower.  Keep going in that direction until the pitch sound
> about in the same range as before.  You are now listening to
> pitch-inverted audio.  It sounds all messed up.
> 
> 
> -Robert Scott
>  Ypsilanti, Michigan
> (Reply through this forum, not by direct e-mail to me, as automatic
> reply address is fake.) 
> 

I don't have access to that hardware, but I've had a different idea: I'll 
put a voice signal into a vocoder, invert all the bins (you can do this 
on my Nord Micromodular) and use white noise as a carrier. It'll be murky 
and full of artifacts, but it should give me some impression. I suppose 
the test will be reversing the process and seeing how legible it is...

-- 
Toby
asktoby.com
BSOD VST & ME

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Toby Newman wrote:

> # Jerry Avins
> 
> 
>>C H wrote:
>>
>>
>>>does anyone know to to spectrally invert a SSB(single side band)
>>>signal both in baseband and passband.
>>>
>>>
>>> from  /¦   to   ¦\
>>>
>>>Thanks
>>> 
>>>ch
>>
>>If you write what you mean by inverting it at baseband, I'll go into
>>detail. (That sort of operation is done in analog voice scramblers.)
>>
>>Jerry
> 
> 
> I'm curious: What is the audible effect of inverting the frequency, say 
> mirroring it about it's average, so a voice signal's upper frequency of ~
> 8kHz becomes 100Hz, and it's first fundamental of ~100Hz becomes 8kHz?
> 
> I'm having difficulty imagining it.

It's every bit as hard to describe as it is to imagine. Even before
1950, there were scrambler telephones. They worked by breaking the voice
spectrum into bands (typically, five), inverting some, and scrambling
them. The processor was reversed at the receiver, restoring
intelligibility if the transmission medium were flat enough in both
response and group delay. I've heard such scrambled speech a few times,
but inverted only once.

For a science project, some students used a reel-to-reel tape recorder
to present speech backward. Spectators were encouraged to repeat the
sounds and be recorded. The best of them -- and all the student
demonstrators -- could be understood by us mortals when their
"reverspeak" was played backwards. Think about Navajo reverspeak! Who
needs fancy technology?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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