Re: cine sound board

> At 11:45 AM 6/10/97 -0500, you wrote:
> >
> > I think you guys were talking about using an LFSR, generated by a PIC to
> do that. Did that work?
>
> I haven't done it with a PIC (but have with a 6800, 6809, Z-80 and a 8088),
> the technique works fine. It's a very simple "shift, rearrange some bits,
> XOR" algorithm. Works just like the schematic on one of those Cinematronics
> games (I can't remember which games used discreet components to implement
> the shift register / noise generator. I thought Star Castle did.)

        Star Castle doesn't. It uses a 3-pin noise generator to generate the "NOISE" signal.

        It sounds like you used a basic LFSR. The output of that LFSR is colored noise (as you found out.) You can shape that noise by doing some other stuff. By putting a Low-Pass filter on it's output (and taking a simple average) you can make that noise have a Normal distribution. Your LPF determines the mean and variance of that distribution. This LPF actually isn't trivial (if you want a good normal distribution) it needs to be somewhere around 10th and 20th order (I'm not sure what your guys' backgrounds are, but if you're familiar with the Central Limit Theorem from Probability, it says that the sum of N independent random distributions is always Normally distributed as N gets large. What's large? About 20 -- Implying that you need a 20th order filter, give or take....)
> It's drawback is the noise generated doesn't have a lot of low end
> component. It works great for gunshots, but lacks real low end rumble on
> ship explosions.
>
> So for the games that used the noisy semiconductor approach (Space War,
> Sundance, Tailgunner(?), I think I'm missing one) the explosions won't sound
> nearly as cool.
>
> -Zonn
>

        Anyways, let me knmow if any of you guys have any info on that noise generator...

Joe
 
Received on Tue Jun 10 12:02:40 1997