Convolution with a constant convolution kernel (constant over time) gives you the response of a time-invariant system to the input signal. A Leslie is clearly not time-invariant.. Flo On 07/26/2012 06:51 PM, Julien Claassen wrote:

On 07/26/2012 07:04 PM, Julien Claassen wrote: I sense a misunderstanding. With a single constant kernel you can only model time-invariant systems. A Leslie is NOT time-invariant. I.e. the response changes with time (the speaker rotates). So what you could do as a workaround would be to get IRs from the Leslie at various positions. Then convolve your input signal with each of them and mix the outputs together with the mixing coefficients being a periodic function of time.. You could probably get away with calculating only a few of the convolutions if your mixing coefficients are sparse, i.e. you only crossfade between two consecutive (in time) output signals.. (keep in mind the window length of the convolution kernel, though).. It's of course a tradeoff - You need quite a few IRs to make the transitions smooth.. But then it's just a matter of hacking some code around an existing convolution engine.. But this could be done with shelf solutions Flo

On Thursday 26 July 2012 13:37:45 Julien Claassen did opine: Speaking as a bit of an engineer, to do a Leslie simulation would require that something like a bucket brigade be done with the digital data once decoded, then setup a pair of taps that would sample the digital from the brigade , advancing the signal in time for the speaker nearest the listener, and delaying the other half of the mix equally. Then combine it, and send it on down the path to the speakers, or perhaps to 2 separate speakers, but the 2 speaker approach would add its own artifacts. What you are then building is in essence similar to a comb filter with a variable clock speed. And this effect would only be valid for a stationary listener, because the bucket-brigade would have to get longer for the angle being synthesized according to where the listener is. The farther off the centerline, the longer the brigade, up to the time lag representing the maximum separation of the actual speakers on the Leslies rotating board. I'm sure some curious coder could work out the math, but the bucket-brigade would probably have to be done in hardware. Such IC's are (or were a decade ago) available. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! Most of our lives are about proving something, either to ourselves or to someone else.

On 07/26/2012 07:00 PM, Florian Paul Schmidt wrote: You'll want angular dependent convolution https://ccrma.stanford.edu/~jos/doppler/dafx02.pdf CCRMA has more publications on that matter.

On 07/26/2012 07:10 PM, Florian Paul Schmidt wrote: You're pretty much describing https://github.com/pantherb/setBfree/blob/master/b_whirl/whirl.c

On Thursday 26 July 2012 16:59:53 Gene Heskett did opine: I forgot to mention that the tap location up and down the bucket brigade would have to be cycled from zero to the max separation at 2x the Leslies speaker rpms in a sin wave pattern. This could be done by keeping the sign of the sine and shifting the channels so they would crossover in time with the sin being driven with the Leslies normal rpm, the crossover of course occurring when the speakers are directly over each other. It might be a fun exercise to code if our modern cpus are fast enough to do the bucket brigade in memory at the sample frequency, for the whole brigade needed. A decent approximation might be done with 8 buckets, but I'd think 16 or 32 deep would be more accurate for the golden eared, which sadly no longer includes me. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! "I'd love to go out with you, but I never go out on days that end in `Y.'"

I can't resist: http://www.youtube.com/watch?v=Y5KaeCZ_AaY

Hello Fons! Nothing technical really or perhaps it is? but is't accident sometimes a huge point of such devices? As far as I remember, it was more or less an accident, that the roland TB303 sounded that crappy, same for one guitar effects processor of the same era, but exactly these accidents made them, what they are today. :-) Smart-Aleck-ingly yours Julien =-=-=-=-=-=-=-=-=-=-=-=- Such Is Life: Very Intensely Adorable; Free And Jubilating Amazement Revels, Dancing On - FLOWERS! ====== Find my music at ====== http://juliencoder.de/nama/music.html ..................................... "If you live to be 100, I hope I live to be 100 minus 1 day, so I never have to live without you." (Winnie the Pooh)