[sci.electronics] Along the heterodyne lines, what about "FM" synthesis?

john@qip.UUCP (John Moore) (09/12/90)

In article <1040@beguine.UUCP> Jeff.Miller@samba.acs.unc.edu (BBS Account) writes:
]Comming from more of an EE background, explanations of FM synthesis
]such as used in the Yamaha DX-7 (mostly by musicians) leave me
]confused. I suspect that what Yamaha passes off as "FM" synthesis
]would be far better described as AM synthesis. 
] 
]People have said "One frequency modulates another." But how how? By
]instantaneous multiplication, like an AM transmitter, or deos one
]frequency wiggle the other in the _frequency_ domain, like an FM
]transmitter? 
I believe the Yamaha uses "Chowning" synthesis. In that method, you
do in fact instantaneously modulate the frequency of one signal
with another. FM modulation gives different effects than AM
modulation. For one thing, a sine wave modulating another sine wave
may have an infinite number of sidebands.

The modulation can be performed all sorts of ways. Basically, just
feed the modulating frequency to a VFO, and you get it.
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jgk@osc.COM (Joe Keane) (09/13/90)

In article <1040@beguine.UUCP> Jeff.Miller@samba.acs.unc.edu (BBS Account)
writes:
>Comming from more of an EE background, explanations of FM synthesis
>such as used in the Yamaha DX-7 (mostly by musicians) leave me
>confused. I suspect that what Yamaha passes off as "FM" synthesis
>would be far better described as AM synthesis. 

It really is frequency modulation.  If you put in a certain control voltage,
the oscillator has a certain frequency.  If you put in a higher control
voltage, the oscillator has a higher frequency.  This is nothing new if the
control voltage is derived from a static source such as the keyboard.  I think
the supposed innovation is that you can use other sources to dynamically
modify the frequency, even changing the phase within a single cycle.

>And while we're at it, isn't a ring modulator just a VCA? Or a special
>case of a VCA with a square wave as one of the inputs? Isn't this the
>same as a chopper?

Yes, a VCA and any modulator do the same thing, which is multiply two signals
together.  I'm not sure about the square wave part, but i do know a ring
modulator is basically a multiplier.