Negative frequency

[Goddard, Duncan]

>>>Negative frequency is when the wavefrom goes just as fast in the
> opposite direction<<<
> 
>>>The interesting stuff happens with the transistion from positive
> frequency to negative frequency.  A "thru-zero VCO" will have a linear
> control voltage that will let you take the waveform down to zero Hz
> and then backwards.<<<
> 
>>>You can PM modulate a low frequency sine wave through zero Hz for a
>   nice chorus animation effect.  (The best DX-7 organ patches do this
>   to emulate a rotating speaker.)
>  And DJ scratching is effectively thru-zero FM.
>   "Wheekwho-wheekwho-wheekwho." <<<
> 
well, I don't know if I get it or not. why is it called "negative frequency"
when all that happens is you turn the frequency down to zero and them back
up again? the most you'll see is a phase change, surely?
and don't "real" rotary algorithms use a combination of vibrato (for doppler
effect) and pan?
sorry for being stupid, I've never come across this phenomenon before.

d. 


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