Hi Alan—extremely cool article, nice job!

This is related to your closing question, but if you have time, I found this 
course very interesting:

Audio Signal Processing for Music Applications

It’s a different thing—the main part pertaining to analysis and re-synthesis in 
the frequency domain, with pitch and time changing and including formant 
handling. It’s not as well suited for real time, since you need to capture 
something in its entirety before analyzing and re-synthesizing (unless you go 
to a lot more work). On the other hand, it knows about pitch and individual 
harmonics, so it allows more sophisticated processing, more akin to melodyne. I 
completed the first offering of it over three years ago, don’t know what 
improvements it might have now. The lab/home work revolves around a python 

If nothing else, it would give you idea about how to deal with formant (which 
will need frequency analysis anyway). You can also audit and just check out the 
course videos pertaining to the harmonic models, for instance.


> On Mar 5, 2018, at 5:45 PM, Alan Wolfe <alan.wo...@gmail.com> wrote:
> Hello rbj!
> My techniques are definitely not that sophisticated. It's really neat to hear 
> what the deeper layers of sophistication are.
> I'm particularly surprised to hear it is in the neighborhood of vocoders. 
> That is another technique I'd like to learn sometime, but sounds "scary" 
> (granular synthesis sounded scary too before I did this post hehe).
> Anyways, all I'm doing is placing grains after another, but repeating or 
> omitting them as needed to make the output buffer get to the target length 
> for whatever percentage the input buffer is at. I only place whole grains 
> into the output buffer.
> There is a parameter that specifies a multiplier for playing the grains back 
> at (to make them slower or faster aka affecting pitch without really 
> affecting length).
> Whenever a grain is placed down, say grain index N, if the previous grain 
> placed down isn't grain index N-1, but is grain index M, it does a cross fade 
> from grain index M+1 to N to keep things continuous.
> In my setup, there is no overlapping of grains except for this cross fading, 
> and no discontinuities.
> I use cubic hermite interpolation to get fractional samples, my grain size is 
> 20 milliseconds and the cross fade time is 2 milliseconds.
> Would you consider this enough in the family of granular synthesis to call it 
> GS for a layman / introduction?
> Thanks so much for the info!
> PS do you happen to know any gentle / short introductions to formants or 
> vocoders?
> On Mar 5, 2018 3:58 PM, "robert bristow-johnson" <r...@audioimagination.com 
> <mailto:r...@audioimagination.com>> wrote:
> this is very cool.  i had not read through everything, but i listened to all 
> of the sound examples.
> so there are two things i want to ask about.  the first is about this 
> "granular" semantic:
> Thing #1:  so the pitch shifting is apparently *not* "formant-corrected" or 
> "formant-preserving".  when you shift up, the voice becomes a little 
> "munchkinized" and when you shift down, Darth Vader (or Satan) comes through. 
>  that's okay (unless one does not want it), but i thought that with granular 
> synthesis (or resynthesis), that the grains that are windowed off and 
> overlap-added where not stretched (for downshifting) nor scrunched (for 
> up-shifting).  i.e. i thought that in granular synthesis, the amount of 
> overlap increases in up shifting and decreases during downshifting.  this 
> kind of pitch shifting is what Keith Lent writes about in Computer Music 
> Journal in 1989 (boy that's a long time ago) and i did a paper in the JAES 
> in, i think, 1995.
> without this formant-preserving operation, i think i would call this either 
> "TDHS" (time-domain harmonic scaling), "OLA" (overlap-add), or "WOLA" 
> (windowed overlap-add), or if pitch detection is done "SOLA" (synchronous 
> overlap-add) or "PSOLA" (pitch synchronous overlap-add).  however i have read 
> somewhere the usage of the term PSOLA to mean this formant-preserving pitch 
> shifting a.la <http://a.la/> Lent (or also a French dude named Hamon).  BTW, 
> IVL Technologies (they did the pitch-shifting products for Digitech) was 
> heavy into this and had a few patents, some i believe are now expired.
> Thing #2: are you doing any pitch detection or some attempt to keep waveforms 
> coherent in either the time-scaling or pitch-shifting applications?  they 
> sound pretty good (the windowing smoothes things out) but might sound more 
> transparent if you could space the input grains by an integer number of 
> periods.
> with pitch-detection and careful cross-fading (and windowing can be thought 
> of as a fade-up function concatenated to a fade-down function) you can make 
> time-scaling or pitch-shifting a monophonic voice or harmonic instrument 
> glitch free.  it can sound *very* good and companies like Eventide have been 
> doing something like that since the early-to-mid 80s.  (ever since the H949.) 
>  and i imagine any modern DAW does this (and some might do frequency-domain 
> pitch-shifting and/or time-scaling using something we usually call a "phase 
> vocoder".
> but your examples sound pretty good.
> r b-j
> ---------------------------- Original Message ----------------------------
> Subject: [music-dsp] granular synth write up / samples / c++
> From: "Alan Wolfe" <alan.wo...@gmail.com <mailto:alan.wo...@gmail.com>>
> Date: Mon, March 5, 2018 5:14 pm
> To: "A discussion list for music-related DSP" <music-dsp@music.columbia.edu 
> <mailto:music-dsp@music.columbia.edu>>
> --------------------------------------------------------------------------
> > Hey Guys,
> >
> > Figured I'd share this here.
> >
> > An explanation of basic granular synth stuff, and some simple standalone
> > C++ i wrote that implements it.
> >
> > https://blog.demofox.org/2018/03/05/granular-audio-synthesis/ 
> > <https://blog.demofox.org/2018/03/05/granular-audio-synthesis/>
> >
> > Kind of amazed at how well it works (:
> >
> > Thanks for the answer to my question BTW Jeff.
> > _______________________________________________
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> > music-dsp@music.columbia.edu <mailto:music-dsp@music.columbia.edu>
> > https://lists.columbia.edu/mailman/listinfo/music-dsp 
> > <https://lists.columbia.edu/mailman/listinfo/music-dsp>
> --
> r b-j                         r...@audioimagination.com 
> <mailto:r...@audioimagination.com>
> "Imagination is more important than knowledge."
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