On Saturday 13 October 2007, Jonatan Liljedahl wrote: >Gene Heskett wrote: [...] >> The fall time of that computer generated sawtooth is probably 100x [...] >This was indeed it. Though I didn't know that a soundfile must not >contain any sharp discontinuities, I thought that the hardware would >filter it out. But you say this is not possible once it's digital, how >come? Why can't you just run a soundfile through a filter to take out >everything above nyquist? (upsampling it first, I guess) If the file was generated via a lookup table, or a simple reset to the - rail when the + rail is hit, then fed directly to a D/A without _any_ resampling to get it to the D/A's fixed clock, I expect it would have worked ok, but when it got re-sampled to make it hit the 44khz or whatever the cycle time of the D/A is, it got eaten up badly. >> Recalculate the sawtooth so that the fall time stays within the >> systems bandwidth, and I'd bet a bottle of suds most of the effect >> you are hearing will go away. The fall time should not be less than >> 1/frequency, answer is in seconds. > >Yes, I found code for bandlimited sawtooth oscillator in the Synthesis >ToolKit which worked very well! Is this the right place to make the obligatory comment about old age & treachery? :-) At 73, I have a hard time hearing some of this stuff, mainly due to whats called 'carhart' notches in my own hearing, measured at 120+ db deep at 4khz. That's from wearing out the first 2 rifle barrels of the 4 I've worn out over the years, without any earmuffs. None the less, aliasing is to my ears as bad, or possibly worse, than fingernails on a blackboard, AKA extremely obvious. Running SSB radio's on chicken band is another place where aliasing really tells you just how good the radios filters are. That makes the best ear training to ident the effect ever invented. Any leakage of the opposite sideband makes it pretty unpleasant. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Weiler's Law: Nothing is impossible for the man who doesn't have to do it himself. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
