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Re: Special kind of frequency sweep (chirp)?
Posted: Tue Nov 01, 2011 9:49 pm
by steve
And here's a bandwidth limited (no aliasing) saw version:
Code: Select all
(setq low-freq 440) ; initial frequency - Hz
(setq hi-freq 1320) ; final frequency - Hz
(setq initial-amp 0.8) ; initial amplitude on a scale 0 to 1
(setq final-amp 0.1) ; final amplitude on a scale 0 to 1
(setq hz1 (min low-freq hi-freq))
(setq hz2 (float (max low-freq hi-freq)))
(setq iamp (max (min initial-amp 1) 0))
(setq famp (max (min final-amp 1) 0))
(setf *blsaw-table*
(let* ((wave (build-harmonic 1 2048)))
(do ((i 2.0 (setq i (1+ i)))) ; all harmonics
((or (>= (* i hz2)(/ *sound-srate* 2.0))(> i 2048)) wave)
(setq wave (sum wave (mult (/ i) (build-harmonic i 2048)))))
(maketable (mult -0.6 wave))))
(mult (pwlv iamp 1 famp)
(fmosc 0
(sum
hz1
(mult
(- hz1 hz2)
(sum -1 (pwev 1 1 0.01))))*blsaw-table*))
Re: Special kind of frequency sweep (chirp)?
Posted: Mon Nov 14, 2011 12:07 am
by Thewoog34
Sorry for bumping this post so many times, but thank you so much, Steve. You were a HUGE help.
Here's my rendition of a Thunderbolt with rotation. It's certainly not perfect, but I like the results. I raised the chopper level a bit (the Thunderbolt had a blower so it could spin the chopper at lower or higher speeds depending on how you set it if you wanted to raise and lower the pitch) so it's higher in pitch. My next target? The
ACA Hurricane.
Re: Special kind of frequency sweep (chirp)?
Posted: Mon Nov 14, 2011 12:19 am
by steve
I'm no expert on sirens, but that sounds really impressive to me
Good luck with the ACA Hurricane.
Re: Special kind of frequency sweep (chirp)?
Posted: Mon Nov 14, 2011 12:27 am
by Thewoog34
I decided to do the
10/16 port Decot instead, cause the ACA Hurricane is pretty much ACA's reponse to the Thunderbolt, blower and all. It was just significantly louder and had a different waveform cause it was 8/10 ports spinning at 3500 RPM instead of 5/6 ports spinning at anywhere from 4,000-8,000 RPM. That'll be up this week.