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Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

blog.demofox.org

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Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#11

Post by ssalazar »

hatsunearu wrote: post #6

Looks like the virtual "string" is shaped as a random string, and then suddenly let go to make that sound. I wonder what would happen if you shaped the original buffer with a certain shape--for instance a linear rampup then a linear rampdown at some point, much like how you would stretch a string. edit: hacked together a string plucking thing here: https://www.shadertoy.com/view/ldVSzd modify the coefficient inside p…

Nice! Another "trick" is to take the buffer with the impulse response of the body of the instrument you are modeling, e.g. a piano soundboard or violin body, and filter the excitation (noise, or ramp, etc.) before putting it in the buffer. You can hear this so-called commuted synthesis[1] being used here [2]-- not exactly Stradivarius but kinda sounds like a screechy violin.

[1] https://ccrma.stanford.edu/~jos/pasp/Commuted_Synthesis.html

[2] https://youtu.be/U8wjFmLQJT4?t=21s

Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#12

Post by Atrix256 »

hatsunearu wrote: post #10
ed wrote: post #9

Here's an editable demo written in JS (just hit "preview"): http://tinyrave.com/tracks/67/remix

Sounds way better than the original author's demo! Original author's demo: https://www.shadertoy.com/view/MdyXRd

The shadertoy was an attempt at doing the algorithm without a delay buffer (making it stateless). The real demo is the wav file and the C++ that generated the wav file (:

Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#13

Post by ssalazar »

You can play around with a lot of this stuff in the ChucK programming language[1]. ChucK was co-created by one of the early advocates for physical modeling sound synthesis, of which Karplus-Strong is an instance. A few examples are in [2] [3] and [4]. Disclosure: I am one of the current developers working on ChucK.

[1] http://chuck.stanford.edu/

[2] http://chuck.stanford.edu/doc/examples/deep/plu.ck

[3] http://chuck.stanford.edu/doc/examples/deep/plu2.ck

[3] http://chuck.stanford.edu/doc/examples/deep/plu3.ck

Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#15

Post by squeaky-clean »

ssalazar wrote: post #11
hatsunearu wrote: post #6

Looks like the virtual "string" is shaped as a random string, and then suddenly let go to make that sound. I wonder what would happen if you shaped the original buffer with a certain shape--for instance a linear rampup then a linear rampdown at some point, much like how you would stretch a string. edit: hacked together a string plucking thing here: https://www.shadertoy.com/view/ldVSzd modify the coefficient inside p…

Nice! Another "trick" is to take the buffer with the impulse response of the body of the instrument you are modeling, e.g. a piano soundboard or violin body, and filter the excitation (noise, or ramp, etc.) before putting it in the buffer. You can hear this so-called commuted synthesis[1] being used here [2]-- not exactly Stradivarius but kinda sounds like a screechy violin. [1] https://ccrma.stanford.edu/~jos/pasp/C…

Accidental downvote, sorry. Thanks for sharing those links!

Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#16

Post by speps »

ssalazar wrote: post #13

You can play around with a lot of this stuff in the ChucK programming language[1]. ChucK was co-created by one of the early advocates for physical modeling sound synthesis, of which Karplus-Strong is an instance. A few examples are in [2] [3] and [4]. Disclosure: I am one of the current developers working on ChucK. [1] http://chuck.stanford.edu/ [2] http://chuck.stanford.edu/doc/examples/deep/plu.ck [3] http://chuck.…

Awesome work, I really love ChucK and participated in the mailing list at some point to work out how to embed ChucK into another app. Conclusion: it wasn't easy as the code has a lot of global static state but I had ChucK as the audio solution for a game I never finished.

Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#18

Post by jusssi »

I have implemented (with a group of two other people) a slightly fancier version of something like this at school, for an exercise at DSP implementation course.

The basic principle was really the same with the circular buffer and a filter, the combo of which can be understood as a long IIR filter. The fancier parts included tunable harmonic bandpass filter (in place of OP's two sample average), and a fractional delay filter for fine-tuning.

By changing the parameters on the bandpass filter it could be made to sound anything from a plucked string to a church bell (minus the reverb since we didn't have that). We were quite surprised how good it sounded.

Unfortunately I seem to have misplaced all the materials related to that course. The hardware we implemented it for was some exotic audio DSP, but we had a matlab model that could produce output samples. If only I could find it.. =/

Re: Synthesizing a Plucked String Sound with the Karplus-Strong Algorithm

#19

Post by kmm »

Fascinating. I implemented a small proof of concept of Mathematica and it sounds remarkably well, especially for such an extremely simple idea.

Maybe a small nitpick, but by using the filter described in this article (taking the average with the next sample), the frequency isn't exactly equal to sample rate / samples per buffer, as the filtering method is asymmetric, and it shifts the signal half a sample to the left every pass. With a more symmetric method, like replacing each value by the average of the surrounding values, that doesn't happen. It may sound pedantic, but the difference is quite clear audible

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