[PD] Bandlimited oscils (was Re: anti-aliasing filtering)

[Dario Sanfilippo]

​Thanks for sharing this, Orm. Is there no bibliography at all about this
implementation?

Cheers,
Dario​


On 29 October 2017 at 05:21, Orm Finnendahl <
orm.finnendahl at selma.hfmdk-frankfurt.de> wrote:

> Hi,
>
>  concerning avoiding aliasing in the first place, here are
> abstractions for generating bandlimited versions of the most popular
> analog waveforms I developed for a seminar some time ago:
>
> https://www.selma.hfmdk-frankfurt.de/selmafile/f/9eed9b01b9/
>
> Open "bl-oscil-example.pd" to see how to use it. Note that the rect~
> oscillator has an additional pulse-width input.
>
> The patch uses wavetable lookup with 128 wavetables of an ideal
> bandlimited sawtooth with partials 1 through 127 for each wavetable
> respectively and the non-bandlimited phasor wavetable for the
> 128th. In the oscillator the wavetable is determined on each phasor
> wraparound based on frequency.
>
> At a samplerate of 44100 Hz this gives no aliasing above 173.6 Hz
> which my ear considered good enough (for 173.6 Hz the aliasing happens
> at about -42 dB for the first aliased partial relative to the first
> partial, diminishing by 6 dB per Octave downwards). Increase the
> number of wavetables for better signal/aliasing ratio.
>
> As this method gives ideal results and is as efficient as it can get
> it's strange I haven't found it on my web research of this topic, but
> maybe I've looked at the wrong places. In times when wavetable lookup
> synthesis has regained popularity in commercial soft-synths I could
> well imagine companies like NI or Ableton also use this or simlar
> methods under the hood of the oscils for their standard analogue
> waveforms.
>
> --
> Orm
>
> Am Samstag, den 28. Oktober 2017 um 19:24:00 Uhr (-0200) schrieb
> Alexandre Torres Porres:
> > 2017-10-28 18:30 GMT-02:00 cyrille henry <ch at chnry.net>: Its very
> > different : a sawtooth have an infinite number of harmonics, but >
> > not a signal distorted with tanh. And a band limited sawtooth is
> > lot's > better (from sound and performance perspective) than an
> > oversampled / > filtered phasor.
> > >
> >
> > yeah, I know it's got infinite harmonics, and that a band-limited
> > oscillator is better. But this is also because I'm using this to measure
> > the efficiency of the anti-aliasing filter, how good it works and all
> >
> > cheers
>
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