I know it would feel like cheating, but that's actually a more proper way of doing acid effects if you're really into analog audio accuracy.
But if you're interested, here are some ways of doing acid effects:
1. Pass the audio through band-pass, band-stop or notch filters.
2. Pass the audio through to an amplifier whose gain is higher than the hardware can physically tolerate.
3. Apply duty cycle or pulse-width modulation to the carrier signal.
Technically, the FDS channel is best for acid effects because you have the ability to change the channel's carrier wave into something more analog (i.e.: non-linear). But, if you want to challenge yourself, VRC6 would work pretty well; if you think about it, a square wave is technically a sine wave that's been amplified to clip-off, so it's only a matter of changing the pulse width.
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so good! now it's just a shame that effect can only be achieved using a bunch of otherwise identical instruments. would make much more sense to do stuff like this using the Vxx command instead.
do you have a rough guide on how you did this? one time i did something similar by morphing a saw into a triangle (by averaging waveform values... 6x triangle, 5x triangle 1x saw, 4x tri 2x saw etc.)
I recorded a WAV of the original Kraken song, and looked for unique waveforms in the intro. I found about 6 of them. I then resampled these so that the wavelength became about 64 samples. I then wrote a program to dump the WAV as text-numbers in the appropriate range, found the waveform loops in this text dump and pasted them into Famitracker.
if you want to streamline that process slightly you could use SPC Tool to rip the samples directly from the Kraken SPC. actually, here, i found 7:
http://vgmusic.com/~lunar/temp/kraken.rar
the nice thing about SPC tool is it only lights up the samples in an SPC that have been triggered, so if you only play the intro of kraken battle in SPC tool you know exactly which samples have been used for that ostinato. loop points are also preserved in the samples on export.
the resampling step of your process sadly doesn't seem like an exact science with different sound lengths/sample rates. that sounds like something that can only be achieved with trial and error. but i dunno, it would be sweet if there was a tool to automate the entire process, from taking a sample, resampling it and converting it to FDS instrument values.
Well, getting the sounds wasn't really what took any time. I've used SNES sample ripping tools in the past but for this they were already there plain in the intro. I've never tried SPC Tool specifically though, because it doesn't seem to run on Windows 7...
Resampling isn't that hard, either. Zoom in on the waveform, measure its length and then:
new samplerate = old samplerate * 64 / length
From there it's a matter of turning it into 6-bit unsigned numbers in a text format that Famitracker will take. This part took me the most time because I had to write a program to do it.
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