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FamiTracker
In "FDS_SriK_-_F%!&_Dis_S#!%" (The song released with newer versions of Famitracker), an FDS bass effect is used (around row 0D) that I was wondering how to make. I was wondering how I could achieve this certain heavy sound using the Jxx effect, and which values I should use for different notes. If anyone has a solution as to how I can calculate the values, or simply a chart that tells me which numbers to use for each note to achieve this sound. Thank you to anyone who can help!
What is going on is that they're using the modulation unit on the FDS at such a fast vibrato that it actually makes FM synthesis. So a basic understanding of 2-operator FM is very very handy here. You can play around with the VRC7 expansion chip if you're not familiar with it.
The first thing is to make the Carrier wave of the FM which is just the FDS wave. The next thing is to make a Modulator wave which is the wave below that (yellow values indicate no change in frequency and blue values reset to initial freq). Next you have to find a good match for the Mod wave + Mod depth. Try using a Modulation Rate of 440 as this will make your Modulator wave play at an A-4. You should also make sure the tracker/instrument preview is also playing an A-4 so that your ModWave to CarrierWav is at a ratio of 1:1 since that's easiest. Then fiddle around with the ModWave and ModDepth (essentially Modulator Volume for our purposes) until you find a combination that produces a somewhat stable FM sound. If we were using Yamaha's way of doing FM, which is actually Phase Modulation, it'd be much easier to find stable sounds. But since this is true FM, it's very hard to find a stable note. In SriK's case, they used a Mod Wave that was all green values right below the yellow values and the mod depth was 63; this made a stable note.
Next thing to do, is erase the Mod Rate back to 0 so that the frequency/implied ratio isn't stuck to just one note per FT instrument. Next thing to find out is what notes you want to play with your Mod wave, so use any table of [url=http://www.phy.mtu.edu/~suits/notefreqs.html]Note Frequencies you can find. Next you have to convert that hertz value to hexidecimal. So if you want a middle C which is 261.63hz, then in hex that's 105. In the tracker the Ixx value should be set to I01 and the Jxx value would be J05, and this will play your ModWave at a C-4. To keep the ratio 1:1, put a note in the pattern as a C-4 so that the CarrierWave will also play that same note. This should play out your FM sound.
One thing to note is that the FDS modulation unit can only do vibratos as fast as 4095 hertz, so the highest note your mod wave could play is I0F JFF. Another thing is that if your Mod wave seems to work with several Mod Depth values, you can leave that field in the FT instrument as 0 as well and then use the Hxx effect in the pattern (in hexidecimal!) to change that value on the fly.
As with FM synthesis, it's not necessary to play your Mod and Carrier at a 1:1 ratio, experiment to get very different FM timbres!
