Feedback in FM synthesis

[Theo]

----- Original Message -----
From: Don Tillman <don at till.com>
To: <t.hogers at home.nl>
Cc: <synth-diy at node12b53.a2000.nl>
Sent: Monday, August 07, 2000 4:52 PM
Subject: Re: Feedback in FM synthesis


> John Chowning's original patent is FM.  US patent 4,018,121:
> http://www.patents.ibm.com/details?pn=US04018121__
>
> But the DX-7 patent is clearly PM.  US patent 4,554,857:
> http://www.patents.ibm.com/details?pn=US04554857__
>
> I don't know why Yamaha choose to use PM instead of FM.  I would think
> that FM would generally sound warmer.
>

Ok I admit, me stupid and me math is crap.
Could someone explain this to me:
(from the dx7 patent)
"For simplifying the operation circuit by substituting a linear
multiplication operation
by a logarithmic addition, the sine wave table 53 stores sine function
values in logarithm."

It is easy to see why this is easyer to implement (takes less cells).
What I don't get is why the logarithmic addition is the same as a linear
multiplication.

Theo