| Yamaha Ym3812 |
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The Yamaha YM3812 also known as the '''OPL2''' (OPL is an Acronym for ''FM Operator Type-L'') is a Sound Chip (i.e. Integrated Circuit ) created by Yamaha Corporation and famous for its wide use in IBM PC -based Sound Card s such as the AdLib and Sound Blaster . It is backwards compatible with the OPL aka YM3526 , to which it is very similar - in fact, it only adds 3 new waveforms. An upgraded version of the OPL2, the OPL3 aka YMF262 , was also popular in later sound cards such as the Soundblaster 16. Another related chip is the YM2413 (OPLL), which is a cut down version. The circuit has 244 different write-only registers. It can produce 9 channels of sound, each made of two oscillators. Each oscillator can produce Sine Wave s which may also be modified into 3 other waveforms - the negative part of the sine can be muted or inverted, and pseudo sawtooth waves (1/4 sine waves upward only with silent sections in between) can also be produced. This odd way of producing waveforms give the YM3812 a characteristic sound. Each wave generator has its own ADSR envelope generator. Its main method of synthesis is Frequency Modulation Synthesis - where one of the channel's oscillators modulates the other. Here's the overview of a channel's registers: For the whole channel: Main frequency (10 bits) Octave (3 bits) Note on/off Synthesis mode (FM or just additive) Feedback (0-7, the modulator modulating itself) For each one of the 2 oscillators: Frequency multiply (can be set to 1/2, 1 to 10, 12 or 15) Waveform (Sine, half-sine, absolute-sine, quarter-sine) Volume (0-63, logarithmic) Attack, Decay, Sustain, Release (4 bits each, logarithmic) Tremolo (On or off) Vibrato (On or off) Sustain (On or off) Envelope scaling per key (On or off) Volume scaling per key (0-3) There's also a few parameters that can be set for the whole chip: Vibrato depth Tremolo depth Percussion mode (uses 3 channels to provide 5 percussion sounds) Composite sine mode (never used and doesn't work on the Opl3) EXTERNAL LINKS |
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