How does the NES produce sampled sounds? What bit size are they?
The fifth NES sound channel is dedicated to producing sampled sounds using two methods. The most basic is by sending RAW sampled values through $4011 at a certain speed to produce a sampled waveform. The second method is the DMA method [also called DMC, for Delta Modulation Channel], which automatically plays short samples for you at a certain bitrate. The DMC method works differently from the RAW method, however, in that 1 bit is read from the sample data at a time, and the value in $4011 is either increased or decreased depending on the value of the bit, which was read. This is why this method is called Delta, because each bit of a sample causes a change either up or down. The size of the sample data in $4011 for the raw method is 7 bits. • How does $4011 work? For RAW sample playing, you just write 7-bit unsigned [as far as known] binary data to $4011, and the level shows up directly as an analogue voltage level on the NES’ audio pin #2. I have made some demos [unreleased] which do
