<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><BR><DIV><DIV>On Apr 30, 2006, at 12:17 PM, Eric Brombaugh wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Due to limited resources an LFO will have to be a separate design. It's come up often enough that I'd be interested in what folks would like to see in an LFO. A few questions:</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><BR class="khtml-block-placeholder"></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">* Frequency range?</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><BR class="khtml-block-placeholder"></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">* Waveforms?</FONT></P> </BLOCKQUOTE></DIV><BR><DIV>An update on my previous comments -- </DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I agree with Paul Maddox that a good frequency range would be from 0.01 Hz to 1000 Hz. Hopefully, your chip can handle that kind of range.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I've been thinking about it a bit, and I'm not too worried that the stepping is going to be too audible at slow rates. This is because you are likely to attenuate the LFO before it hits its destination, and thus, would also be attenuating any stepping noise. Most pitch mod is less than one octave, which would mean attenuating your 10 Volt output swing to just one Volt. That would make the steps pretty insignificant. Filter sweeps tend to span more octaves, but usually not ten octaves -- more like 3 to 5 octaves at the most. It'll be interesting to see how audible the stepping will be for wide filter sweeps.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Regarding waveforms, I think it would be really cool if you could include a table for a so-called "hypertriangle" wave. This is a triangle that has a kind of exponential change in amplitude over time. That is, as it starts ramping upward, it ramps faster and faster as it approaches its peak, then as it ramps downward, it does the opposite: it gradually slows down as it approaches its lowest point. This type of LFO can be very musical, especially when using it to modulate flangers and phasers. You can check out audio examples of this at Scott Stites' DIY 32-stage phaser website. It's pretty dramatic, and after you hear the phaser with the hypertriangle modulation, you don't really want to hear it again with a normal triangle. It just seems to make the sweep sound more smooth, natural, and musical at both the low and high ends of the sweep. There's probably a technical explanation for this, but I don't know what it is. I'm going to guess that the hypertri LFO is also good for modulating highly resonant LP, HP, and BP filters at slow rates, although I haven't heard it done yet.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I don't know if an inverted hypertriangle would also be useful (start ramping up fast, then slow down as you approach the peak). So far, all the applications I have seen use one that starts ramping slow, gradually speeding up towards the peak. Still, I have a hunch that there might be some good apps for the inverted one, too.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I guess if you wanted to save lookup table ROM space, you could always invert externally via analog means (same goes for the inverted saw, too)</DIV><DIV> </DIV><DIV>You can find Scott's most recent stuff at this URL:</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><A href="http://mypeoplepc.com/members/scottnoanh/birthofasynth/id18.html">http://mypeoplepc.com/members/scottnoanh/birthofasynth/id18.html</A></DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>I'm sure Scott could also give you some tips as to how that wave should look. I think he generates his hypertriangle by putting a nonlinear element (an FET that distorts the wave?) into a standard triangle wave oscillator circuit. It can also be achieved with a voltage controlled LFO by outputting a standard linear-ramp triangle wave, and then feeding a small amount of the triangle output back into the LFO's CV input. As the wave amplitude rises, so does this feedback CV, causing the wave to speed up faster and faster as the CV rises higher and higher, then reversing the process and slowing down on the way back down.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Mike B.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV></BODY></HTML>