On Thursday 15 December 2005 18:06, Phil Frost wrote: > There is truth in what you say, but given the problem described, this is > likely more confusing than helpful to someone new to signal processing. > > If the problem is that the input is a low frequency square wave, from a > Low Frequency Oscilator, the popping has nothing to do with the > "nyquest" limit. If the square wave were coming from an ideal source > (which it isn't) then any higher frequency components likely would be so > small as to be smaller than the quantization error.
The thing is that a LFO implemented as part of a plugin is an ideal source for all practical purposes, it can and does do a step change in sample value (for the nieve squarewave case) which if the LFO is running at 20Hz gives the level of the 1001st harmonic as 1/1001 that of the fundamental, or some 60db down. Low but hardly buried in the nose, as the mixing products will not be harmonically related to either signal. > The problem is simply that it contains high frequency components (under > the limit), or more intuitively, a sudden drop or rise. Drop or rise > more slowly, and the pops go away. Does hooking the LFO output directly to a speaker click, if so this is the problem, but if it only acts up when multiplied with another signal then I still maintain that it is mixer products aliasing that is the problem. > There is no need here for a high order filter here, and no risk of phase > shifts or overshoot. A simple first order lowpass filter will be quite > effective, as will any other simple techniques such as averaging or > changing the LFO function to put more slope on the rising and falling > edges. Also the OP probably needs to make the rate of change continuous as that can also cause a click. Regards, Dan.
