> > I read (a fairly scholarly) paper on modular synthesis Oww. I sprained my tweaky finger when I read this. Hope you don't mind if I comp along in the background while you engineers go on a bit. [Hhreene breenay whooommple plink. Plakelee pladaa squeeedle deedle doodlee oomple.] [DC al Coda] Ed Edwards Leader: Ezekiel's Wheel \ufffd\ufffd\ufffd\ufffdRetro-Progressive Rock\ufffd\ufffd\ufffd\ufffd http://www.ezekielswheel.com http://www.untiedmusic.com/ezekiel http://www.headholemines.blogspot.com \ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd\ufffd.\ufffd\ufffd > -----Original Message----- > From: AN1x-list@yahoogroups.com [mailto:AN1x-list@yahoogroups.com]On > Behalf Of Dan > Sent: Monday, April 18, 2005 5:10 PM > To: AN1x-list@yahoogroups.com > Subject: Re: [AN1x] Aliasing > > > > for the > Nord > > Micro Modular and it said unequivocally that digital oscillators > have > > more energy above 10,000 Hz than their analog counterparts > ============================ > Here's part of the article that I was referencing: > > http://www.cim.mcgill.ca/%7Eclark/nordmodularbook/nm_oscillator.html > > > "Rob Hordijk has developed a very nice sounding "analog" style > filter. His filter avoids the "buzzy" sound produced by many digital > resonant filters. The buzziness arises because digital oscillators > contain a relatively large amount of energy above 10kHz. Most analog > oscillators have less energy in this region, as the analog circuitry > itself filters part of it away. Imagine a sawtooth set to 200 Hz, > therefore having overtones 200 Hz apart from each other. This means > that in the area between 10 kHz and 20 kHz there are 50 overtones > present, all crowded together within a single octave! When using, > for example, 3 slightly detuned oscillators you're talking about 3 * > 50 = 150 overtones all in that one high octave, and all phasing fast > with each other. The amplitudes of these overtones are very small, > but there are a lot of them and very high sounds are perceived quite > well, so there is a distinct buzz in the high. If the cutoff > frequency is set to this area the buzziness is increased even more > at high resonance levels. The resonance band of a 12 dB filter is a > bit broader than that of a 24 dB filter, so the 12 dB filter suffers > a bit more from the buzz. > > The problem with this buzz is that it can mess up those other sounds > that have by nature lots of energy in the same band, notably hihats > and cymbals and some dipthongs in the vocals. Thus it is a good > practice to filter everything above 10kHz away from all instruments > when there are hihats and cymbals in the rhythm track, or if you use > vocals from someone with a clear voice. Otherwise these hihats and > the s's and t's will drown in the high of the other instruments. Its > even worse if the 10kHz+ area gets in a reverb with a very bright > tail. That will start to produce lots of noise. > > For most synth sounds, especially strings, its not the 10kHz+ area > which is important, but the area between 3.5kHz and 10 kHz. So > filtering away all above 10kHz but slightly emphasizing the 3.5 to 8 > kHz area greatly improves the warmth and depth of stringsounds. A > single 6 dB LP filter set to 10kHz won't do the job, the cutoff > frequency should be set to 2.5 kHz or less to effectively remove the > buzz. Even the cutoff frequency of a 24 dB filter should be set to > something like 5kHz. But in both cases you would also lose part of > the important 3.5 to 8 kHz area. The most useful solution is to use > a dipfilter with a notch around 12 kHz. > > The filter is composed of two 12 dB filters that are cascaded to get > a 24 dB filter. On the first filter a little bit of the HP output is > mixed to the LP output. This is tuned by a MasterOsc module. As it > apparently needs some bizarre overexponential control to get > everything right, the grey signal is raised to the power of two and > mixed with the grey signal to control the amount of HP. This creates > a notch at the top end of the spectrum, which does three things: > > 1) it attenuates the very high end, making the filter less "buzzy ". > 2) it reduces the resonance at the top end of the spectrum relative > to the rest of the spectrum, especially at high resonance settings. > This also makes the sound less buzzy. > 3) the notch increases the filter slope slightly. > > The messing about with that grey signal is just to keep the notch at > the right place, which is tuned to taste by ear. > > The second 12dB filter increases the filter cutoff slope to 24 dB. > The feedback from the LP output of the second filter increases the > bottom end of the spectrum, giving the sound a little bit more guts. > > This filter can give good analog bass sounds with even a single > sawtooth oscillator. " > > > > > > > > > > > > Community email addresses: > Post message: AN1x-list@yahoogroups.com > Subscribe: AN1x-list-subscribe@yahoogroups.com > Unsubscribe: AN1x-list-unsubscribe@yahoogroups.com > List owner: AN1x-list-owner@yahoogroups.com > > Shortcut URL to this page: > http://groups.yahoo.com/group/AN1x-list > > The AN1x Control Synthesizer FAQ:: > http://www.geocities.com/jondl_2000/an1x_faq/an1x_faq_toc.htm > > Yahoo! Groups Links > > > > > > >
Message
RE: [AN1x] Aliasing
2005-04-19 by Ed Edwards