<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Uhhh, not exactly.<div class=""><br class=""></div><div class="">The "k" value is the tuning of the operator with respect to the note being played. So it's 1 by default. It's not time varying.</div><div class=""><br class=""></div><div class="">The phase modulation happens in Fig 8. The carrier phase value is kwt. The modulator phase value is f(wt), which is the enveloped signal from another operator with its own k value. They are added, which would be the phase modulation, and then sent to the sine lookup table.</div><div class=""><br class=""></div><div class="">(By the way, I'm loving this discussion.)</div><div class=""><br class=""></div><div class=""> -- Don</div><div class=""><div class=""><div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">--<br class="">Donald Tillman, Palo Alto, California<br class=""><a href="https://www.till.com" class="">https://www.till.com</a></div></div>
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<div><br class=""><blockquote type="cite" class=""><div class="">On Nov 27, 2022, at 11:15 PM, Ian Fritz via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">With a careful reading of the Yamaha patent it is easy to understand how the FM signal of the DX7 is generated. The algo is quite simple:<br class=""><br class="">1) A keypress produces a carrier wave with a frequency w (omega)<br class=""><br class="">2) This frequency is multiplied (modulated) by a time-varying signal called a scale factor k. The resulting product is the instantaneous frequency of the system.<br class=""><br class="">3) The instantaneous frequency values thus calculated are fed to an accumulator, which produces the time-integrated value of the instantaneous frequency. This is the phase of the output signal.<br class=""><br class="">This is a calculation of a standard frequency-modulated signal. This is obviously FM, simply because the frequency is what is modulated (not the phase).<br class=""><br class="">This algo is EXACTLY analagous to the analog circuitry we use for making FM modules:<br class=""><br class="">1) A carrier frequency is generated via the V/Oct input and the usual exponential control current generator<br class=""><br class="">2) This current is multiplied by the value of the signal fed to the Lin FM input<br class=""><br class="">3) This product is fed to the integrater which is part of any VCO to produce the FM signal<br class=""><br class="">Looks to me that Chowning and Yamaha are correct in saying the DX7 is an FM synth.<br class=""><br class="">Ian<br class=""></div></div></blockquote></div>\</div></body></html>