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| [[Category:APU]]
| | #REDIRECT [[APU Mixer]] |
| The [[APU Mixer|NES APU Mixer]] can be efficiently emulated using a lookup table or a less-accurate linear approximation.
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| == Lookup Table ==
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| The APU mixer formulas can be efficiently implemented using two lookup tables: a 31-entry table for the two [[APU Pulse|pulse channels]] and a 203-entry table for the remaining channels (due to the approximation of tnd_out, the numerators are adjusted slightly to preserve the normalized output range).
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| <pre>
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| output = pulse_out + tnd_out
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| pulse_table [n] = 95.52 / (8128.0 / n + 100)
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| pulse_out = pulse_table [pulse1 + pulse2]
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| </pre>
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| The tnd_out table is approximated (within 4%) by using a base unit close to the [[APU DMC|DMC's]] DAC.
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| <pre>
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| tnd_table [n] = 163.67 / (24329.0 / n + 100)
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| tnd_out = tnd_table [3 * triangle + 2 * noise + dmc]
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| </pre>
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| == Linear Approximation ==
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| A linear approximation can also be used, which results in slightly louder DMC samples, but otherwise fairly accurate operation since the wave channels use a small portion of the transfer curve. The overall volume will be reduced due to the headroom required by the DMC approximation.
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| <pre>
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| output = pulse_out + tnd_out
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| pulse_out = 0.00752 * (pulse1 + pulse2)
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| tnd_out = 0.00851 * triangle + 0.00494 * noise + 0.00335 * dmc
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| </pre>
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