I would checkout rjlib and the s_osc~ which has bandlimited oscillators ... no need to reinvent the wheel. rjlib is vanilla so it will work fine with libpd.
Also, if you want the analog sound, the creb/moog~ external is kosher for the App store. I have it in PdParty. On Dec 20, 2013, at 5:27 PM, pd-list-requ...@iem.at wrote: > From: Tony Hillerson <tony.hiller...@gmail.com> > Subject: [PD] A naive approach to bandlimiting > Date: December 20, 2013 at 5:26:59 PM EST > To: pd-list@iem.at > > > Hey guys, > > I’m building an iOS and Android app with an “analog" synth component. I’m > pretty inexperienced with the DSP world, and my math and theoretical > understanding of things is pretty rudimentary. Because I’m building a mobile > app, I feel like I need to build each of the components of the synth myself > instead, to avoid issues such as those with the App store and the GPL. > > I’ve built the oscillator array, now and I have something I’d like to run by > this group. I understand enough of the problem of band limiting to know the > ill effect to the sound, and that there are a few different approaches people > take to solve it. I don’t quite understand enough of how these solutions > work, though to know if there’s “a solution” that I should use. After > thinking about the problem I tried the approach I lay out below, and I’d like > feedback. Is it a naive way of solving the problem? Does it introduce other > problems? Is it really inefficient? Here goes: > > I have nine tables, which I populate with a collection of geometric wave data > using sinesum. Each table has fewer harmonics than the last. Then I use an > array of [moses] objects to check the incoming MIDI note and call a "set > <tablename>" on a [tabosc4~] before each note is played. > > I choose a table with fewer harmonics as the note gets higher, and the > boundary is generally the B note in the next octave. So, to produce a > sawtooth wave, I have a wavetable with 714 partials for MIDI notes 24 and > below, 357 partials for MIDI 36 down to 25, 178 partials from MIDI 48 to 37, > and so on until between 128 and 109 I use a table with a single sine wave. > > My naive understanding is that this approach is fairly efficient with CPU, > but not efficient with memory. I believe it will let me have nice fat low-end > notes, but should never have any aliasing as notes go higher in the register. > > Anyhow, I hope that was clear enough. What of this approach? > > -- > Tony Hillerson -------- Dan Wilcox @danomatika danomatika.com robotcowboy.com
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