Asteroids sounds, or how do 555 set-ups differ ?

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Well....since I'm working on my Asterock (an Asteroids bootleg by an Italian company called Sidam) I've been delving into the sounds of Asteroids.

But first here's a little video of the very first run:

http://youtu.be/ImOo-Zdzo-s

Now listen to the sounds. Please ignore the explosion sounds which sound distorted, but that is caused by this:
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So focus on the ship firing, instead of the PIIIIEEEEUUUWWWW sound you normally get on Asteroids, I now have a very irritating, constant "BEEP" that stays the same in volume and frequency.

Also, the saucers do not produce any sound when they fire !

I checked the Asterock schematics and, it's very clear why the saucers do not produce fire sound:

Here's part of the original Asteroids schematic:
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and here's the same part for the Asterock schematic:
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Very clear: pin 5, which is Saucer Fire Enable is simply not hooked up to anything ! (I do think it's triggered, but I'll have to measure that).

Anyway, I might be able to live with that.

BUT, the ship fire sound is TOTALLY annoying. It is way too loud compared to the rest of the sounds, and just gives you a head-ache if you play for a while.(esp. repeated shots).
 
So focus on the ship firing, instead of the PIIIIEEEEUUUWWWW sound you normally get on Asteroids, I now have a very irritating, constant "BEEP" that stays the same in volume and frequency.

BUT, the ship fire sound is TOTALLY annoying. It is way too loud compared to the rest of the sounds, and just gives you a head-ache if you play for a while.(esp. repeated shots).

Well, you've apparently got the schematics for (Atari) Asteroids. On the same page you posted a shot from, there's the ship shot sound (SHPFIRESND) schemtic, and an paragraph that explains the circuit a little: "...this signal begins to decay immediately, both in frequency and amplitude, due to the discharge of the control capacitors (C38 & C39 for Saucer Fire Sound, C47 & C48 for Ship Fire Sound)." Compare the Atari audio schem of the ship fire circuit to your Asterock (for which I don't have schematics, but you appear to).

If you just want to "turn down the volume" on the ship fire sound, you could increase the value of the resistor in the mixing circuit for that sound (each sound has a seperate resistor which effects its relative volume level as they are mixed together).
 
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Pics...

Pics attached showing:
-the full shipfiresnd circuit (including the caps that cause the decay).
-the explaination written by Atari in the schems
-the mixing circuit, showing each sound source being mixed thru a resistor network

Not having Asterock schematics, I can't compare to how it's done there. But I suppose they may have cut costs and just grabbed a fixed frequency rather than bother with the fully circuitry required to make the decaying sound effect. They may just use a 555 timer to control the duration of the beep(? just guessing). The add'l transistor, op-amp, and switches in Atari's circuit may or may not be there in an Asterock. Will be interesting to see.

In any case, there must be some sort of mixing circuitry in Asterock, and with that you could at least dial back the volume of it.
 

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So once again I compared the schematics to see if I could "copy" the original Atari set-up to the Asterock PCB.

Original Atari Asteroids:
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From what Atari describes in the manual C47 and C48 (yellow blocks) are responsible for lowering both the frequency and the amplitude of the fire sound produced.
The yellow arrow shows the "Input" SHPFIREEN signal, the green the output SHPFIRESOUND signal.

It's not totally clear what the switches do (4016) They are also controlled by SHPFIREEN. I think the leftmost part of the 4016 in the red oval starts charging C47 as soon as SHPFIREEN is on. The Capacitor takes a little while to charge, and through L8 and Q5 this controls the DIS signal on the 555. Anyway, I can understand that this is adjusting the frequency of the 555 sawtooth and thus changing it.

I think (about) the same happens on C48 but I don't fully understand how that is controlling the amplitude like that, and what the diode on pin 3 of the 555 is for.

Now.....even ignoring ALL of that, if I compare to the Asterock schematic, I see that the output of the 555 is NOT HOOKED UP to anything, instead they seem to use the "sawtooth" from the TR and TH (See the green "SHPFIRESND" arrows).

web.jpg


I find this completely weird, but it could explain why I hear the loud and constant BEEP for the fire shots.

Now, normally I'm all for originality, and for Asterock, this may be original, but I just can't stand it, so I was hoping if there would be an "easy" way to re-create the sound like the original. There seems to be no 4016 switches on the Asterock, nor the Caps that do the controlling....

Any tips, or help explaining how the original Atari set-up EXACTLY works is highly appreciated !!
 
Thanks Darren, I was still writing "part 2 (because of the IMG limit) while you responded...

Have a look, what do you think ?

I think I agree with your assessment. The 555 in the Asterock looks pointless; its output isn't connected (for that matter, the schematic shows the power, pin 8, also not connected...). From looking at it, I would expect the exact same sound if the 555 were completely removed (care to desolder it to find out?).

It looks to me like (in Atari Asteroids) the 555 is used in "astable" mode (ref: http://en.wikipedia.org/wiki/555_timer#Astable_mode ) and the upper part of the diagram controls the frequency, with Q5 effectively functioning as a variable resistor to change the 555's output freq. R66 & C48 form a RC circuit with a time constant of about 0.03s, and they cause the volume to fade. When SHPFIREEN is active, it resets the 555, and activates both of the 4066 switches, which causes the freq and volume "sweep" effect, all at the same time. Doesn't look like there's any easy way to mod Asterock to do all that... You might be able to make the volume fade by adding a cap in series with R88(?), but making the frequency shift would be a lot more work.

Oh, and it looks like the reason your ship fire sound is so loud is... Atari used a 100k resistor for it in mixing, Asterock has a 22k (R55). Most of the other values are more or less the same in both games.
 
Well, I could "copy" the Atari circuits on some Veroboard.

As long as I hook it up between the outputs of the LS259 and the "mixing" resistors it should be fine shouldn't it (disabling the original circuits of course.)

About the 555 being not needed, it does keep the saw-tooth on the TR and TH going right ?
Anyway, I'll compare the actual PCB traces to the schematics, who knows they made a mistake in the schematics.

I have one other alternative: I have a fully working original Asteroids PCB. Although "technically" it would be wrong to use that, I think it would work fine.

The only problem is having to make an adapter, and also, Asteroids expects 36 VAC input to make some other voltages, and Asterock has already "changed" these to +22V and -22V, but I can hook up these voltages right before the 78xx's and 79xx.

This would also open the possibility of adding a Braze Mulit Kit. IF it ever becomes available.

However, it would be cool to succeed in adding the "correct" sounds to the Asterock hardware.

Also, the coin-up signals on Asteroids are positive instead of negative...so weird that Speleo, who fixed the board, couldn't credit it, but it works fine in the cab....
 
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OK, entering the schematic into SPARK to see if I can make a little daughter board.

Looks like Atari forgot something in their schematic:

M9 (or M10 in red) 4016 pin 3 and R60 seem to be hooked up to "nothing". I guess it's to +5V but not sure.....will have to check my Asteroids PCB...
 
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