In 2006, two MSX developers created an advanced encoder that converts a wave file to optimal PSG channel transitions using a Viterbi search. They replayed a 44.1 kHz wave file on a 23 year old MSX and achieved a higher signal-to-noise ratio than an 8-bit DAC. The Viterbi search is rather CPU intensive, so even though it would have been theoretically possible to use this method already in the 80's, there were no computers powerful enough to perform the analysis required.