The Bubble Bobble Fiasco

[1024MAK]

@TMD2003

Having seen what the SID effects look like on an oscilloscope I now know that this is created by a square wave that's "more up than down" or "more down than up"

The technical term for this is PWM, or Pulse Width Modulation, a common technique used on most synthesizers, alongside triangle, ramp (sawtooth), and plain 50/50 duty cycle square waves. Pure sine waves are generally less common as an audio oscillator, as they have no harmonics, but are used to modulate other aspects of a sound, for example PWM!

Ahh, but the frequency of the level switching has to high (fast) enough so that a human ear only hears the average. Otherwise it sounds horrible.

The technical term for this is PWM...

Now you mention it, I have heard of that term, most likely on the same video where I saw what the SID waveform looked like.

Is it impossible on the AY, or was it just a lot easier on the SID so that all the Commie/Amiga programmers used it all the time?

On sound chips like the General Instrument AY-3-8910, AY-3-8912, AY-3-8913, the Yamaha YM2149F and the Texas Instruments SN76489, (a slightly crude form of) PWM can be achieved by altering the volume from minimum to maximum and vice versa. That’s similar to how samples are played back on these sound generator chips. It is rather processor intensive though.

[media]https://youtu.be/4xVfuuSty48[/media]
( link )

Mark

[RR7]

With regards to the music, the copy of Bubble bobble i had was on the taito coin-op hits compilation, it had the loader with the countdown timer on the loading screen, and on my grey +2 in 128K mode there was no music. Which i found disappointing.

however, i discovered if i held the button down to start the game, then the music played, but it resulted in graphics corruption on the bubbles.

I don't know if such a thing can be tested under emulation.

EDIT: confirmed! here is how to re-produce, at least in Spectaculator

load the game from the coin-op hits version (tape 2 side A)

if you select controls, such as pressing 2 for sinclair then 3 for kempston, the press 1 or 2 page appears with no music, the game plays normal.
if you select controls, by pressing 2 but then keep pressing 3 repeatedly, the music starts and then the 1 or 2 page appears, but the bubble graphic appear corrupted.

it doesn't seem to care if i choose +2 or +2A

EDIT2: the Original version with the firebird bleed loader thing works properly, as I'm sure everyone already knows.

EDIT:3 the hit squad one is the same as the compilation one, (typed before I read Stu's reply!)

[RR7]

maybe someone can have a look and see if it was done on purpose due to the change in loading scheme, or if it's just a bad side effect no-one noticed or cared about.

EDIT: sorry just re-read and understood this:

There's a noticeable delay after you select the player controls, and what seems to be happening there (for those interested - starting at 0xfac3) is a timing check - the end result being if you've loaded the tape on a +3 then the music is explicitly switched off. Odd that there's no problem with the disk version though

if you load it in pentagon mode, the music is enabled again (different timing?), with the graphics corruption, so i guess they discovered this error when they changed the loading scheme and hacked in the disabling of the music if it detects that specific timing. i don't see any re-release or compilation disk version.

perhaps mashing a button on that screen disturbs the timing measurement somehow and fools the code into not disabling the music, revealing the corrupted graphics.