<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">I'll pipe in and add: ac-coupled FM is still just FM, but with "high passed" modulation, assuming some reasonable input resistance before the cap. if you have no appreciable series resistance, the differentiator is ideal-ish but will clip at higher modulation frequencies. if you -do- add a series resistor, the differentiator will have unity gain somewhere up in the pass band, so a sine wave above some frequency would be identical in both schemes. <div><br></div><div>even though it's comparable, I feel like calling this PM is subtly incorrect. differentiated FM is "FM that is always trying to decay to 0", which is not precisely modulating phase. pedantic, or wrong, I donno. <div><br><div dir="ltr">Cheers,<div>Chris </div></div><div dir="ltr"><br><blockquote type="cite">On Jun 26, 2023, at 4:32 PM, Neil Johnson via Synth-diy <synth-diy@synth-diy.org> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><div dir="ltr"><div>Hi,</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, 26 Jun 2023 at 22:20, Mattias Rickardsson <<a href="mailto:mr@analogue.org">mr@analogue.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto">Neil Johnson <<a href="mailto:neil.johnson71@gmail.com" target="_blank">neil.johnson71@gmail.com</a>> skrev:<div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>...</div><div class="gmail_quote"><div>Purists will pop up and say that when the modulating signal is a sine wave there is no difference between the two, and that's fine (lets ignore the pi/2 difference between sin and cos, eh?).</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">Surely the amplitudes differ, right? And the modulation depth that follows. Louder treble and weaker bass in a differentiated sine wave. :-)</div></div></blockquote><div><br></div><div>Only because your differentiator is rubbish!</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto"><br></div><div dir="auto">PS: I'm often thinking of the "local DC offsets" of modulated or suddenly started sounds, and how to deal with that. Don't know if it's normal. </div></div></blockquote><div><br></div><div>That's why we have window functions in DSP :)</div><div><br></div><div>Neil</div><div> </div></div></div>
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