Ghostbusters

The sing-along

The theme song, with a bouncing ball over 52 lines of lyrics

The title screen plays Ray Parker Jr.'s theme in Russell Lieblich's arrangement while a ball bounces along the words.⁴⁵ The music stops when the song ends, four minutes later. In play the same tune loops quietly behind the game.

The game's own music player ($93E1-$95A4) ported to JavaScript and played through the site's model of the SID. The port was checked against the game's code, register write for register write: 223,366 writes over 111,904 frames matched. The lyric window follows the game's cue table ($68F0) and the ball's script ($92BC): each line and landing is at the frame the game shows it, measured in the simulator. Title is the sing-along, played once. In play is the loop at half volume.

The tune is three voices of patterns: a melody, a bass line and a percussion track, each a list of 109 pattern numbers ($A2BD, $A32B, $A399) into 71 patterns ($A407) and nine instruments ($A7EF). The player steps every fourth tick of a counter ($08) that the lyrics share, so the words and the notes cannot drift apart.

The game was written for American machines. At start-up it measures the screen's last raster line to tell a European (PAL) C64 from an American one (NTSC) and stores the answer at $EA73. A PAL machine draws 50 frames a second where an NTSC machine draws 60, so on PAL the counter takes an extra step whenever it lands on a value ending in binary 001: eight ticks in seven frames, 57.3 a second. The tempo comes out close to the American one. The pitch does not. The note table ($A1F4) holds the SID values for an NTSC clock, where note 57 is exactly 440 Hz. A PAL C64 runs 3.7 % slower, so every note of the song sounds 0.65 of a semitone flat.

Speech

Five phrases of speech from 2,738 bytes, and one the game never says

The game shouts "Ghostbusters!" at start-up and when the space bar is pressed on the title screen. It speaks four phrases in play. A fifth, phrase 0, is stored with the others and never asked for.

The game's speech player ($F080-$F4E9) ported to JavaScript and run on the stored phrases ($F4EA-$FF9B). The port writes the same 311,368 values to the volume register, at the same interrupts, as the game does in the simulator. Top: the four-bit level the player writes, 9,659 times a second. Middle: each frame of the phrase, blue where it is voiced and orange where it is noise. Bottom: the pitch of each voiced period. Heard here as a straight level; a real SID shapes it a little.

Phrase	Length	When the game plays it	What it says
0	0.94 s	never	its first blocks are phrase 1's; probably a shorter "Ghostbusters" (inferred)
1	1.57 s	start-up; space on the title (`$6393`); a Slimer trapped (`$8820`)	"Ghostbusters!"
2	1.32 s	a man slimed (`$874B`)	"He slimed me!" (inferred from where it plays)
3	2.68 s	start-up; a man caught at Zuul (`$8AB9`); the foreclosure (`$8D1F`)	a laugh: nine voiced syllables (inferred)
4	2.22 s	the portal closing (`$8C5A`)	unknown: a falling voice with no consonants

Speech on the C64 has no sound chip of its own. The player plays it through the SID's master volume register ($D418): a four-bit value written there moves the output level, and written fast enough it becomes a waveform. A timer in the second CIA chip interrupts the processor every 102 cycles, and each interrupt writes the next value. While a phrase plays the game does nothing else: the raster interrupt stands aside and the main loop waits ($8DB9).

Stored as raw samples, the 8.7 seconds of speech would take 42,140 bytes, two thirds of the machine. The player stores 2,738. A voiced sound is a short waveform chunk played forwards, then backwards, then a silence whose length sets the pitch; each new chunk is blended halfway into the last. A hiss is a one-bit pattern slid along as a window, with no pitch at all. Each frame of a phrase is four bytes that say which, how long and where its samples are.