Misc sound-info on the NES (Nintendo Entertainment System).

About:
   This document is based on simple sample analasys, some of the info may
   actually be correct (but donīt count on it). It was done on my PAL-NES
   (board from 1987) with a "Turtle Beach Montego" sound card.
   Everything is sampled directly from leg 1 and 2 on the CPU in the NES
   (to get past the filters and to separate some of the channels from each
   other), all samples were made in 48kHz 16 bit.

The 2 audio out from the CPU contain 5 channels in total.
leg 1: Square wave 1 and 2.
leg 2: Triangle wave, noise and PCM.



Square Wave (from leg1):
------------------------
  No information available.


Triangle Wave (from leg2):
--------------------------
   The triangle seem to have only 16 steps for the amplitude.
   Reason for this is, after analysing the samples from several games I
   could clearly see the steps and smal noise, it was easier to see on
   the low frequency tones then the high ones, but with a high enough
   sampling-rate it should be possible to measure it there too.

   Another thing I took notice of was that the top and the bottom step
   was twice as long in time as the other steps.
   When counted on a low tone, the difference was 14 to 28,
   so i think itīs quite accurate.
   In ASCII it would look something like this:

  __                      Top --> __
 _  _                            _  _    |         |
     _                          _    _   V Silence V
      _                        _      ________________
       _                      _                       _
        _                    _                         _
         _                  _
          _                _
           _              _
            _            _
             _          _
              _ Bottom _
               _  |   _
                _ |  _
                 _V _
                  __


Well you get the idea.



Noise (from leg2):
------------------
  No information available.


PCM-channel (from leg2):
------------------------

   The sample data used for the DMA method is 1-bit delta. The
   actual format of the data is currently unknown, as is the latency of
   playback.

   When I studied the output (DMA version) from some games it looked like this:

      /\/\
   /\/    \/\
             \/\/\

   It looks very analogue compared to the triangle wave or
   the noise (not to talk about the square waves ;).