Gameboy Sound Information

Four types of Sound generators:

• Quadrangular wave patterns with sweep and envelope functions.
• Quadrangular wave patterns with envelope functions.
• Voluntary wave patterns from wave RAM.
• White noise with an envelope function.

Noise Channel

NR41 Sound Length

Bit 0 - 5 is sound length data (t1).

Sound length = (64 - t1) * (1/256) seconds

NR42 Volume Envelope

• Bit 7 - 4: Initial volume (0 - 0x0F)
• Bit 3 : Envelope direction (0: Decrease, 1: Increase)
• Bit 2 - 0: Number of envelope sweep (0-7)

Length of 1 step = n * (1/64) seconds

NR43 Polynomial Counter

• Bit 7 - 4: Shift clock frequency (s)
• Bit 3: Count step/width (0 = 15 bits, 1 = 7 bits)
• Bit 2 - 0: Dividing Ratio of Frequencies (r)

Frequency = 524288 hz / r / 2^(s+1); For r = 0 -> r = 0.5

NR44 Counter

• Bit 7: Initial (1-Restart sound)
• Bit 6: Counter/consecutive selection (1=Stop output when length in NR41 expires)