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<TITLE>RE: Feedback in FM synthesis</TITLE>
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<P><FONT SIZE=2>> -----Original Message-----</FONT>
<BR><FONT SIZE=2>> From: Martin Czech [<A HREF="mailto:czech@Micronas.Com">mailto:czech@Micronas.Com</A>]</FONT>
<BR><FONT SIZE=2>> Sent: Tuesday, August 08, 2000 9:30 AM</FONT>
<BR><FONT SIZE=2>> To: don@till.com</FONT>
<BR><FONT SIZE=2>> Cc: synth-diy@node12b53.a2000.nl</FONT>
<BR><FONT SIZE=2>> Subject: Re: Feedback in FM synthesis</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> :::John Chowning's original patent is FM. US patent 4,018,121:</FONT>
<BR><FONT SIZE=2>> :::<A HREF="http://www.patents.ibm.com/details?pn=US04018121__" TARGET="_blank">http://www.patents.ibm.com/details?pn=US04018121__</A></FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> In this patent I see the formula:</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> e=A*sin(wc*t+I*sin(wm*t)) (page 19 of 32, second row, line 7 or so)</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> I think I is intended as modulation parameter independend from wm.</FONT>
<BR><FONT SIZE=2>> If this is the case, this formula describes PM and not FM.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> For FM it should be:</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> e=A*sin(wc*t+I/wm*sin(wm*t)) </FONT>
</P>
<P><FONT SIZE=2>and what about this:</FONT>
</P>
<P><FONT SIZE=2>(I implemented it this way)</FONT>
</P>
<P><FONT SIZE=2>e=Ac*sin((Fc+sin(Fm*t)*Am)*t)</FONT>
</P>
<P><FONT SIZE=2>One thing I noticed is that it creates very dull sounds, not bright. There are no sharp peaks.</FONT>
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<P><FONT SIZE=2>JJ</FONT>
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