Replace 2A03/FDS audio cores with NSFPlay/Mesen #32
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Shift-JIS doesn't have ~ and \, and the ASCII/UTF-8 codepoints for those map to overline and yen. https://stackoverflow.com/questions/56819615/ As a result, we have to postprocess the output of iconv. fd -t f -x iconv -f SHIFT-JIS -t UTF-8 {} -o {} fd -t f -x sed 's/‾/~/g; s/¥/\\/g;' {} -i Additionally, iconv corrupts emu2413.c by turning "OPLL_reset(OPLL" into "OPLL_rePLL_reLL". So I had to revert this change.
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Saves CPU in debug builds.
Blip_Buffer::mix_samples() delays all incoming samples by the same amount as Blip_Synth::offset() delays deltas. This is the right choice for audio generated by output-rate synths (used in FamiTracker for VRC7 audio), but causes audio generated by another Blip_Buffer (and already delayed) to be delayed twice. I add a new method, Blip_Buffer::mix_samples_raw(), which does not delay incoming audio, and use it for mixing in filtered FDS audio.
The old code delayed global output by 1 sample, and also delayed CFDS by 1 sample relative to other sound chips.
The constructor with parameters is currently unused.
The nsfplay emulator's APU2 triangle wave has a nonzero offset when reset. This may or may not be accurate. Either way, subtract the offset when the chip resets.
This way, when switching between sound chip emulators with different output levels, we only need to edit the sound chip class to compensate, not any code in CMixer.
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This was referenced Feb 26, 2021
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rip out the guts, replace with something new, reimplement all the side-channel observability metadata (pitch/volume view, register view, channel meters) that comes with it
hopefully i didn't regress any functionality in the process... it'll be done someday, someday~
Overview
2A03 and FDS audio emulation were replaced with nsfplay and Mesen's cores, respectively.
Both are wrapped in CSoundChip2, a newly added replacement for CSoundChip (which was the wrong abstraction). CSoundChip2 does not use CChannel. CChannel was a mistake, and CChannel plus CMixer's current API (each channel independently streams volume levels and/or deltas to the same Blip_Synth located in CMixer) is hostile to any form of channel mixing other than linear mixing.
CSoundChip2 expects to own a Blip_Synth (and CFDS also owns a Blip_Buffer used for lowpass emulation), and does not hold an aliased pointer to CMixer or Blip_Buffer (instead receiving a borrowed Blip_Buffer& whenever audio needs to be generated).
The mixing interface is still inconsistent; CFDS computes mixing levels internally (encapsulating the implementation detail of the emulation core's output levels), whereas C2A03 lets CMixer compute mixing levels.
Behavioral changes
2A03 noise at the highest pitch may use more CPU than before due to emulation inefficiencies. This is only an issue on debug builds or possibly slow computers (did not test). FDS may use less CPU than before due to cycle-skipping.
FDS emulation changes
FDS sounds different due to the lowpass filter added. Additionally earlier FDS instruments will no longer work; the new sine preset will fix the sound with minimal audible changes on older FamiTracker versions.
TODO In the future, we may add a FDS filter strength slider.
The NSF driver performs a modulator phase reset that in-tracker playback does not, making reset-free modulator envelopes that operate deterministically in NSF export start at random positions in the tracker; modulator phase reset may be added into the tracker into the future.
TODO In the future, we may add a toggle for the FDS's non-monotonic jagged DAC (which scrambles wavetable amplitudes but does not affect their position in time).
Volume meter algorithm changes
On affected chips, the volume meters were rewritten to plot the range of volume levels seen during each engine tick, rather than the largest new volume level seen during a tick (where steady-state chip output is interpreted as 0 volume).
For example, the 2A03 DPCM meter now plots the range of DPCM counter values seen, rather than the largest new DPCM counter value. This more accurately models perceived sample volume:
Note that this assumes all steps are evenly spaced, and does not take into account nonlinearity (output deltas being smaller at high values), but it's closer than before.
2A03 triangle waves will flicker more than before (they were never flicker-free) at very low pitches (below 60 Hz).
Potential issues
The latest commit (373331c) was written on Linux and I did not try compiling it. Hopefully it builds on CI, doesn't have warnings, and works properly (on Wine?)