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2a03 (soundchip)


  1. Specifications
  2. Triangle Channel
  3. Noise Channel
  4. DPCM
  5. Consoles
  6. Development
  7. Competition
  8. See also
NSF is the sound file format for the Ricoh 2A03 chip used in the Nintendo NES/Famicom game console. The NSF filetype also supports additional sound expansion chips.

The 2A03 has five sound channels: two pulse waves, one triangle, one noise, and one DPCM channel.


The 2a03, internally controlled by a 6502 microchip, has five sound channels:
- two pulse wave channels,
- one triangle wave channel,
- one (white) noise channel, and
- one DPCM (sample) channel.

Pulse Channel
The pulse channel -- similar to the square wave -- has volume control of sixteen levels and a variable duty cycle of 12.5%, 25%, 50%, 75%, with hardware pitch pending supporting frequencies from 28Hz to 54kHz. Pulse waves are commonly used as lead instruments because of the ability to combine the two channels into one lead sound or combined as chords. It also has a neat 'phasing' feature by playing two different notes to create a duophonic sound by playing the same notes or frequencies on both channels while one channel has a slight pitch bending effect assigned to it. This creates a duophonic sound and/or a sound similar to a synthesizer's oscillator.

Triangle Channel

The triangle channel -- similar to a sine wave -- is a fixed volume and is capable of frequencies from 27 Hz to 56 kHz. (Volume may be changed by increasing or decreasing the DC levels of the DPCM channel or by the pitch of the triangle channel itself.) Like the square wave, the triangle wave produces odd harmonics -- as opposed to even harmonics, but because the triangle's higher harmonics the roll off is much faster than the square wave (or pulse wave) which creates a sound closer to even harmonics. This could explain the pleasing sound a triangle has when used as a lead instrument.

Noise Channel

The noise channel produces white noise. White noise is a random flat signal that crosses over frequencies, also called spectral density.
White noise has the ability to cut through sound as well as absorb other sounds (frequencies). The NES noise channel has sixteen-volume levels and has two modes. Each mode can be adjusted via the linear feedback shift register at sixteen programmed frequencies. There are two modes of playback: Short pattern, and long pattern. Long pattern likens to the term "white noise". It is a hissing or crunching noise. Short pattern's output is not as random as long pattern and outputs certain detuned high frequencies or more defined sounds, due to less randomness.


The DPCM channel has six bits of range and uses 1-bit delta encoding at sixteen preprogrammed samples rates from 4.2 kHz to 33.5 kHz. This channel was also capable of playing standard pulse-code modulation (PCM) sound by writing individual 7-bit values at timed intervals.


The soundchip is used in the following consoles:
- NES/Famicom


NSF file format specs available from Kevin Horton at CLICK HERE


- nsf (format)
- nsfplus (format)
- famitracker (format)

See also

All related Lyceum articles:
referencing to:
- NES Famicom (console)

Sound Chips
2a03 · adlib · AY YM · SID · spc · Z80 · zxbeep