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furnace/papers/doc/7-systems/nes.md
tildearrow 9a1447e392 NES: envelope and length counter effects
2022-10-25 00:43:03 -05:00

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NES

the console from Nintendo that plays Super Mario Bros. and helped revive the agonizing video game market in the US during mid-80s.

also known as Famicom. it is a five-channel sound generator: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and fifth is a (D)PCM sample channel.

effects

  • 11xx: write to delta modulation counter.
    • this may be used to attenuate the triangle and noise channels.
    • will not work if a sample is playing.
  • 12xx: set duty cycle or noise mode of channel.
    • may be 0-3 for the pulse channels and 0-1 for the noise channel.
  • 13xy: setup sweep up.
    • x is the time.
    • y is the shift.
    • set to 0 to disable it.
  • 14xy: setup sweep down.
    • x is the time.
    • y is the shift.
    • set to 0 to disable it.
  • 15xx: set envelope mode.
    • 0: envelope + length counter (volume represents envelope duration).
    • 1: length counter (volume represents output volume).
    • 2: looping envelope (volume represents envelope duration).
    • 3: constant volume (default; volume represents output volume).
    • pulse and noise channels only.
    • you may need to apply a phase reset (using the macro) to make the envelope effective.
  • 16xx: set length counter.
    • see table below for possible values.
    • this will trigger phase reset.
  • 17xx: set frame counter mode.
    • 0: 4-step.
      • NTSC: 120Hz sweeps and lengths; 240Hz envelope.
      • PAL: 100Hz sweeps and lengths; 200Hz envelope.
      • Dendy: 118.9Hz sweeps and lengths; 237.8Hz envelope.
    • 1: 5-step.
      • NTSC: 96Hz sweeps and lengths; 192Hz envelope.
      • PAL: 80Hz sweeps and lengths; 160Hz envelope.
      • Dendy: 95.1Hz sweeps and lengths; 190.2Hz envelope.
  • 18xx: set PCM channel mode.
    • 00: PCM (software).
    • 01: DPCM (hardware).
    • when in DPCM mode, samples will sound muffled (due to its nature), availables pitches are limited and loop point is ignored.

length counter table

val raw NTSC PAL Dendy NTSC 5-step PAL 5-step Dendy 5-step
00 10 83ms 100ms 84ms 104ms 125ms 105ms
01 254 2.1s 2.5s 2.1s 2.6s 3.2s 2.7s
02 20 166ms 200ms 168ms 208ms 250ms 210ms
03 2 17ms 20ms 17ms 21ms 25ms 21ms
04 40 333ms 400ms 336ms 417ms 500ms 421ms
05 4 33ms 40ms 34ms 42ms 50ms 42ms
06 80 667ms 800ms 673ms 833ms 1.0s 841ms
07 6 50ms 60ms 50ms 63ms 75ms 63ms
08 160 1.3s 1.6s 1.3s 1.7s 2.0s 1.7s
09 8 67ms 80ms 67ms 83ms 100ms 84ms
0A 60 500ms 600ms 505ms 625ms 750ms 631ms
0B 10 83ms 100ms 84ms 104ms 125ms 105ms
0C 14 117ms 140ms 118ms 146ms 175ms 147ms
0D 12 100ms 120ms 101ms 125ms 150ms 126ms
0E 26 217ms 260ms 219ms 271ms 325ms 273ms
0F 14 117ms 140ms 118ms 145ms 175ms 147ms
10 12 100ms 120ms 101ms 125ms 150ms 126ms
11 16 133ms 160ms 135ms 167ms 200ms 168ms
12 24 200ms 240ms 202ms 250ms 300ms 252ms
13 18 150ms 180ms 151ms 188ms 225ms 189ms
14 48 400ms 480ms 404ms 500ms 600ms 505ms
15 20 167ms 200ms 168ms 208ms 250ms 210ms
16 96 800ms 960ms 807ms 1.0s 1.2s 1.0s
17 22 183ms 220ms 185ms 229ms 275ms 231ms
18 192 1.6s 1.9s 1.6s 2.0s 2.4s 2.0s
19 24 200ms 240ms 202ms 250ms 300ms 252ms
1A 72 600ms 720ms 606ms 750ms 900ms 757ms
1B 26 217ms 260ms 219ms 271ms 325ms 273ms
1C 16 133ms 160ms 135ms 167ms 200ms 168ms
1D 28 233ms 280ms 235ms 292ms 350ms 294ms
1E 32 267ms 320ms 269ms 333ms 400ms 336ms
1F 30 250ms 300ms 252ms 313ms 375ms 315ms

reference: NESdev