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 Family Computer (Famicom), especially in Japan.

the console is powered by the Ricoh 2A03, a CPU with sound generator built-in. it has five channels: 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. range is 00 to 7F.
• this may be used to attenuate the triangle and noise channels; at 7F, they will be at about 57% volume.
• will not work if a sample is playing.
• 12xx: set duty cycle or noise mode of channel.
• may be 0 to 3 for the pulse channels:
  • 0: 12.5%
  • 1: 25%
  • 2: 50%
  • 3: 75%
• may be 0 or 1 for the noise channel:
  • 0: long (15-bit LFSR, 32767-step)
  • 1: short (9-bit LFSR, 93-step)
• 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 value. 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.
• 19xx: set triangle linear counter.
• 00 to 7F set the counter.
• 80 and higher halt it.
• 20xx: set DPCM frequency.
• only works in DPCM mode.
• see table below for possible values.

info

this chip uses the NES instrument editor.

chip config

the following options are available in the Chip Manager window:

• Clock rate: sets the rate at which the chip will run.
• DPCM channel mode: allows you to set which mode to use for the DPCM channel.
• DPCM: the default mode, playing 1-bit DPCM samples as supported by the hardware.
• PCM: this mode provides crispier samples by writing the delta counter directly. uses a lot of CPU time in console.

DPCM sample loop

due to hardware limitations, a loop in a DPCM sample must start on a multiple of 512 samples (512, 1024, 1536...) and have a length that is a multiple of 128 plus 8 samples (136, 264, 392...)

short noise frequencies (NTSC)

reference: NESdev

length counter table

reference: NESdev

DPCM frequency table

reference: NESdev