Nintendo 1504166 Programming Manual - Page 104
Sound PWM Control, SOUNDBIAS [d15 - 14] Amplitude Resolution/Sampling Cycle
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AGB Programming Manual Sound 10.8 Sound PWM Control Bit modulation format PWM is used in the AGB sound circuit. When no sound is produced, the duty waveform is output, and bias voltage is provided. The PWM circuit is stopped when the setting for duty is 0h. This register uses system ROM. This can be the cause of errors, therefore be careful not to write to this register. Address 088h Register SOUND BIAS 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 Attributes Initial Value R/W 0200h Amplitude Resolution/Sampling Cycle Bias Levels SOUNDBIAS [d15 - 14] Amplitude Resolution/Sampling Cycle This sets the amplitude resolution and sampling cycle frequency during PWM modulation. The DMG compatible sound is input at 4 bits/130.93KHz so in order to have accurate modulation the sampling frequency must be set high. Direct sound will arbitrarily decide the sampling frequency based on the timer setting. By using the sampling frequencies listed in the table below, an accurate modulation can be done. Thus, in order to increase authenticity of sound, the amplitude resolution needs to be set higher. When producing both compatible sound and direct sound find a value that will work for both and set this. Setting 00 01 10 11 Amplitude Resolution 9bit 8bit 7bit 6bit Sampling Frequency 32.768KHz 65.536KHz 131.072KHz 262.144KHz Input Waveform(Waveform Composition for All Sounds) PWM Conversion Image PWM Modulation CPU Output Waveform Amplitude Resolution Time Base Resolution (Sampling Frequency) ©1999 - 2001 Nintendo of America Inc. 104 D.C.N. AGB-06-0001-002B4