Sometimes I find aeolus's pedal range a little limiting. This morning I had the idea of taking a recording of a harley I'd gotten off the intertubes and turning it into a pedal stop for aeolus.
To do this, I first extracted a few seconds of fairly continuous harley sound. I applied a log scale FFT and extracted the harmonics (autocorrelation suggested a fundamental of about 25Hz, with most of the power in the 4th, 6th, 8th and 10th harmonics). I then transfered this into the .ae0 file. The low fundamental meant I had to play around with aeolus to add a 64' option, and fix the loop length calculation code to allow very long samples (up to half a second) for low stops.
After much fiddling I coaxed aeolus, jackd, qjackctl and qarecord(qarecord --jack --rate 48000) to all play nice (most important was to tell them all to use the same sample rate - something they should do automagically) I managed to record an ogg of BWV540 with harley on the pedal.
Such a stop is really overused in this recording. My original motivation was to just use it for the pedal note drone in the opening of BWV540. It doesn't sound great when you move around a lot, probably mostly because it has a fundamental of 25Hz or lower meaning it needs to sound for a long time to avoid dissonance. Runs sound great though (people have asked for a gear change sound :).
I made a 128' version of this, which sounded like a helicopter or ship engine. To do so you need to allow aeolus to look for longer cycles (I think it tries to find a reasonable LCM of the cycle length and sample frequency to make good joins):
- looplen (f1 * fsamp, _k_s * fsamp, (int)(fsamp / 6.0f), &_l1, &nc); + looplen (f1 * fsamp, _k_s * fsamp, (int)(fsamp / 3.0f), &_l1, &nc);
It wouldn't actually be hard to implement this stop. (obviously you could just buy a set of harleys and tune them, but that's cheating) It's essentially a 64' reed stop with a little care on the resonator pipe. Here is a recording of the Sydney Town Hall organ's 64' stop. Apparently they disabled it when plaster chunks fell off the roof after a practice with it.