<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Generator" CONTENT="MS Exchange Server version 5.5.2652.35">
<TITLE>RE: Feedback in FM synthesis</TITLE>
</HEAD>
<BODY>
<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: Friday, August 04, 2000 9:20 AM</FONT>
<BR><FONT SIZE=2>> To: J.Proveniers@orga.nl</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>> Yes, output back to input. Thsi should be </FONT>
<BR><FONT SIZE=2>> equivalent to a inifinite chain of operators,</FONT>
<BR><FONT SIZE=2>> all with the same settings. So the output is harmonic</FONT>
<BR><FONT SIZE=2>> with all harmonics present, that is likely to be</FONT>
<BR><FONT SIZE=2>> sawish.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> You did not give the actual formulas, so it is hard</FONT>
<BR><FONT SIZE=2>> to tell why things do not work.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> Is the sample rate high enough?</FONT>
<BR><FONT SIZE=2>> Feedback causes a lot of high frequency energy, this</FONT>
<BR><FONT SIZE=2>> causes alias problems. Lots of feedback will finaly give noise.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> FM synths therefore run</FONT>
<BR><FONT SIZE=2>> at pretty high sample rates 60kHz +.</FONT>
<BR><FONT SIZE=2>> But it is not very likely that this is your</FONT>
<BR><FONT SIZE=2>> problem.</FONT>
</P>
<P><FONT SIZE=2>I quickly tried this a minute ago</FONT>
</P>
<P><FONT SIZE=2>for (phase=0;phase<360;phase++)</FONT>
<BR><FONT SIZE=2> {</FONT>
<BR><FONT SIZE=2> out=sin((phase+out)/180.0*PI);</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> ...some graphing here...</FONT>
<BR><FONT SIZE=2> }</FONT>
</P>
<BR>
<P><FONT SIZE=2>and that indeed works as I expect. Probably I should take a look closer look to my implementation.</FONT>
</P>
<P><FONT SIZE=2>JJ</FONT>
</P>
</BODY>
</HTML>