On 4/5/15 5:02 PM, Didier Dambrin wrote:
All harmonics (thus, not that many to compute, especially as most fade
out to inaudibility pretty quickly), and not evolving
you mean the phase (let's say relative to the oscillator with the
fundamental) is not changing while the note evolves? certainly the
amplitudes of these oscillators are evolving according to some envelope.
(-just- like with karplus strong, which is pretty much a single-cycle
self-filtering over time)
yup, BUT, with Karplus-Strong, there are two filters in the feedback
loop (and they can be teamed-up and called a single filter, if you
want). one filter is to get a fractional-sample precision delay and the
other is a low-pass filter so that higher overtones die away faster than
the lower. now we can do everything in a phase-linear way, so that the
phase delay of either filter is independent of frequency (BTW, phase
delay is what's salient in Karplus-Strong rather than group delay). to
keep it phase linear, you would have to use some kinda polyphase FIR
interpolation to get the fractional sample delay and another FIR
implementation of the LPF. and Karplus and Strong depicted the latter
in their original CMJ article. if it's all phase-linear, the overtones
are harmonic.
but, you *could* use an IIR LPF and an IIR APF for the fractional sample
delay. then the loop delay will be slightly different for the different
overtones and the frequency of those overtones will not be precisely
harmonic. i would imagine for realistic strings, one would want the
loop delay to be less for higher frequencies than for lower frequencies,
thus tuning the higher overtones sharper than their precise harmonic value.
BTW, i've always considered waveguide synthesis to **be** the method of
physical modeling. maybe i'm missing something basic.
It can sound exactly the same, with the added benefit that you have
full control on the filtering.
lemme understand the claim: Karplus-Strong can be made to be
perceptually identical to the straight sample playback of a particular
plucked-string instrument?
i have to think about that one. it seems to me that every overtone
decay would be strictly exponential, although different overtones can
have different "alphas" and decay at different rates. but you would
have to modify K-S a bit more, like have *two* precision delay lines in
series and two feedback paths in order to have an envelope that would
increase in time before it begins to decay exponentially. or maybe
three precision delays with three feedback paths to have a natural
tremelo on some harmonic as it decays. i dunno.
r b-j
-----Message d'origine----- From: robert bristow-johnson
Sent: Sunday, April 05, 2015 9:23 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Uses of Fourier Synthesis?
On 4/5/15 3:11 PM, Didier Dambrin wrote:
I've created plucked strings using additive (not FFT), and it sounds
the same as a Karplus Strong, but with more control. So it's
definitely doable.
The key is: all oscillators have to be phase-unrelated, or it won't
sound metallic.
are the oscillators harmonic? or not quite harmonic?
if the former, do the relative phases change while the note evolves?
--
r b-j r...@audioimagination.com
"Imagination is more important than knowledge."
--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp
