I've put up the Excel spreadsheet I've been working on over the past few days. It generates typical analogue synthesizer-style sounds and applies a 6dB/octave digital filter to them. (IIR, infinite impulse response) It outputs data which is "almost" ready to go into an SCC (column D). You may want to perform some amplitude and offset adjustments using the formula for column D, which at the moment is just a simple rounding operator.
http://student.cusu.cam.ac.uk/~rga24/computer/msx/SCC%20Blaffer%20Instruments/ Other sounds possible with this spreadsheet are some Yamaha "FM" sounds (really Phase Modulation) with modulator index and carrier to modulator frequency ratio parameters, and additive synthesis sounds such as a organ sound and a major chord. This can also have the filter applied to them, although be aware that filtering a sine wave just gives a lower amplitude sine wave. Change a few parameters here and there, and see what you like! To "capture" a cycle of sound, I used the last filtered cycle in the spreadsheet (roughly rows 96 - 128). This is to allow for some settling of the DC level in the filtered sound. You can change the initial DC level of the filtered sound in cell C1. There are some example waves on the second sheet. If anyone needs any more documentation, just ask. I'm including a transcript of an IRC session 'cos I'm too lazy to type any more atm :) Richard <vortexion> i have to explain how to use it <vortexion> It's in FM mode as shipped <vortexion> Try changing the index and ratio numbers <TwZ|Chaos> ok <vortexion> Also change fc (cutoff) <vortexion> fc is 0.25 on the sheet <vortexion> seen anything change yet? <TwZ|Chaos> I'll start it now <vortexion> The main thing is, there's lots of different columns for different types of start sounds <TwZ|Chaos> yeah <vortexion> sine, saw, triangle, pulse, Yamaha FM and Additive synthesis <vortexion> copy the entire column you want into the column B, under "Start value" <vortexion> Then the graphs will show that sound and the filter will work on it too <vortexion> Column B has Yamaha FM in it to begin with <vortexion> to change settings, just change the numbers in J2 or J3 <vortexion> when you try pulse sounds, L1 has the pulse width <vortexion> and when you try additive sounds, N1, N2, N3 and N4 have the frequencies <vortexion> 1,2,4,8 gives a Yamaha DX7 style organ sound <vortexion> I *hope* ;) <vortexion> 4,5,6,8 is a major chord <vortexion> If you don't want to filter a sound at all, use a cutoff of 1 <vortexion> the lower the cutoff, the more strong the filtering <vortexion> 0 cutoff is no sound at all ;) <TwZ|Chaos> wow.. wait a sec ;) -- For info, see http://www.stack.nl/~wynke/MSX/listinfo.html
