Internal Operation
The internal operation of the chip is completely digital. Each FM-tone is generated by a digital oscillator using a form of direct digital synthesis. A quarter of the log-transformed sine waveform is stored as a sampled approximation in a 256-word read-only memory (ROM) table. The rest of the sine-waveform is extrapolated via its property of symmetry. Scaling the output of an oscillator to a wanted volume would normally be done by multiplication, but the YM3812 avoids multiplications by operating on log-transformed signals, which reduces multiplications into computationally cheaper additions. Another 256-word ROM stores the exponential function as a lookup table, used to convert the logarithmic scale signal back to linear scale when required, as the final stage where the oscillator-outputs are summed together (just prior to the DAC-output bus.) The YM3812's output, a sequence of floating point numbers clocked at a sampling frequency of approximately 49716 Hz, is sent to a separate digital-to-analog converter (DAC) chip, the YM3014B.
Read more about this topic: Yamaha YM3812
Famous quotes containing the words internal and/or operation:
“The real essence, the internal qualities, and constitution of even the meanest object, is hid from our view; something there is in every drop of water, every grain of sand, which it is beyond the power of human understanding to fathom or comprehend. But it is evident ... that we are influenced by false principles to that degree as to mistrust our senses, and think we know nothing of those things which we perfectly comprehend.”
—George Berkeley (1685–1753)
“Waiting for the race to become official, he began to feel as if he had as much effect on the final outcome of the operation as a single piece of a jumbo jigsaw puzzle has to its predetermined final design. Only the addition of the missing fragments of the puzzle would reveal if the picture was as he guessed it would be.”
—Stanley Kubrick (b. 1928)