<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr"></div><div dir="ltr">Interesting discussion!</div><div dir="ltr"><br></div><div dir="ltr">I ran across this EDN article and want to try it out when I get a chance. Seems like a good compromise between and RC and full blown active filter. Has anyone done this before for synths? I wonder if it’s practical for this application.</div><div dir="ltr"><br></div><div dir="ltr"><a href="https://www.edn.com/cancel-pwm-dac-ripple-with-analog-subtraction/">https://www.edn.com/cancel-pwm-dac-ripple-with-analog-subtraction/</a></div><div dir="ltr"><br></div><div dir="ltr"><br></div><div dir="ltr"><br><blockquote type="cite">On Nov 5, 2022, at 12:02 PM, Eric Brombaugh via Synth-diy <synth-diy@synth-diy.org> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr"><span>Correct - range is 1/3 of the original, but much more linear and you can usually make up for that with gain elsewhere in the system. I used this approach (along with differential outputs) in my FPGA oscillator project:</span><br><span></span><br><span>https://github.com/emeb/up5k_osc</span><br><span></span><br><span>Eric</span><br><span></span><br><span>On 11/5/22 08:28, René Schmitz wrote:</span><br><blockquote type="cite"><span>On 05.11.2022 16:04, Eric Brombaugh via Synth-diy wrote:</span><br></blockquote><blockquote type="cite"><blockquote type="cite"><span>There's a way to mitigate that - ensure that you always have a high and low transition in every cycle. Basically you create a very high frequency PWM signal that's either 33% or 67% depending on the state of your PDM bit, so the speed of the high & low transitions are always part of your output and don't vary with the data value. Downside is that your PDM bitrate has to be 1/3 of that you'd get without doing this approach.</span><br></blockquote></blockquote><blockquote type="cite"><span>If I understand correctly, you also loose 2/3 of the output range. And assumes the t_on and t_off are the same.</span><br></blockquote><span>_______________________________________________</span><br><span>Synth-diy mailing list</span><br><span>Synth-diy@synth-diy.org</span><br><span>http://synth-diy.org/mailman/listinfo/synth-diy</span><br><span>Selling or trading? Use marketplace@synth-diy.org</span><br></div></blockquote></body></html>