mirror of https://github.com/bsnes-emu/bsnes.git
6 Commits
| Author | SHA1 | Message | Date |
|---|---|---|---|
Tim Allen
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04072b278b |
Update to v102r16 release.
byuu says:
Changelog:
- Emulator::Stream now allows adding low-pass and high-pass filters
dynamically
- also accepts a pass# count; each pass is a second-order biquad
butterworth IIR filter
- Emulator::Stream no longer automatically filters out >20KHz
frequencies for all streams
- FC: added 20Hz high-pass filter; 20KHz low-pass filter
- GB: removed simple 'magic constant' high-pass filter of unknown
cutoff frequency (missed this one in the last WIP)
- GB,SGB,GBC: added 20Hz high-pass filter; 20KHz low-pass filter
- MS,GG,MD/PSG: added 20Hz high-pass filter; 20KHz low-pass filter
- MD: added save state support (but it's completely broken for now;
sorry)
- MD/YM2612: fixed Voice#3 per-operator pitch support (fixes sound
effects in Streets of Rage, etc)
- PCE: added 20Hz high-pass filter; 20KHz low-pass filter
- WS,WSC: added 20Hz high-pass filter; 20KHz low-pass filter
So, the point of the low-pass filters is to remove frequencies above
human hearing. If we don't do this, then resampling will introduce
aliasing that results in sounds that are audible to the human ear. Which
basically an annoying buzzing sound. You'll definitely hear the
improvement from these in games like Mega Man 2 on the NES. Of course,
these already existed before, so this WIP won't sound better than
previous WIPs.
The high-pass filters are a little more complicated. Their main role is
to remove DC bias and help to center the audio stream. I don't
understand how they do this at all, but ... that's what everyone who
knows what they're talking about says, thus ... so be it.
I have set all of the high-pass filters to 20Hz, which is below the
limit of human hearing. Now this is where it gets really interesting ...
technically, some of these systems actually cut off a lot of range. For
instance, the GBA should technically use an 800Hz high-pass filter when
output is done through the system's speakers. But of course, if you plug
in headphones, you can hear the lower frequencies.
Now 800Hz ... you definitely can hear. At that level, nearly all of the
bass is stripped out and the audio is very tinny. Just like the real
system. But for now, I don't want to emulate the audio being crushed
that badly.
I'm sticking with 20Hz everywhere since it won't negatively affect audio
quality. In fact, you should not be able to hear any difference between
this WIP and the previous WIP. But theoretically, DC bias should mostly
be removed as a result of these new filters. It may be that we need to
raise the values on some cores in the future, but I don't want to do
that until we know for certain that we have to.
What I can say is that compared to even older WIPs than r15 ... the
removal of the simple one-pole low-pass and high-pass filters with the
newer three-pass, second-order filters should result in much better
attenuation (less distortion of audible frequencies.) Probably not
enough to be noticeable in a blind test, though.
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Tim Allen
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7e7003fd29 |
Update to v102r15 release.
byuu says:
Changelog:
- nall: added DSP::IIR::OnePole (which is a first-order IIR filter)
- FC/APU: removed strong highpass, weak hipass filters (and the
dummied out lowpass filter)
- MS,GG,MD/PSG: removed lowpass filter
- MS,GG,MD/PSG: audio was not being centered properly; removed
centering for now
- MD/YM2612: fixed clipping of accumulator from 18 signed bits to 14
signed bits (-0x2000 to +0x1fff) [Cydrak]
- MD/YM2612: removed lowpass filter
- PCE/PSG: audio was not being centered properly; removed centering
for now
First thing is that I've removed all of the ad-hoc audio filtering.
Emulator::Stream intrinsically provides a three-pass, second-order
biquad IIR butterworth lowpass filter that clips frequencies above 20KHz
with very good attenuation (as good as IIR gets, anyway.)
It doesn't really make sense to have the various cores running
additional lowpass filters. If we want to filter frequencies below
20KHz, then I can adapt Emulator::Audio::createStream() to take a cutoff
frequency value, and we can do it all at once, with much better quality.
Right now, I don't know what frequencies are best to cut off the various
other audio cores, so they're just gone for now.
As for the highpass filters for the Famicom core, well ... you don't get
aliasing from resampling low frequencies. And generally speaking, too
low a frequency will be inaudible anyway. All these were doing was
killing possible bass (if they were too strong.) We can add them again,
but only if someone can convert Ryphecha's ad-hoc magic integers into a
frequency cutoff. In which case, I'll use my biquad IIR filter to do it
even better. On this note, it may prove useful to do this for the MD PSG
as well, to try and head off unnecessary clamping when mixing with the
YM2612.
Finally, there was the audio centering issue that affected the
MS,GG,MD,PCE,SG cores. It was flooring the "silent" audio level, which
was resulting in extremely heavy distortion if you tried listening to
higan and, say, audacious at the same time. Without the botched
centering, this distortion is completely gone now.
However, without any centering, we've halved the potential volume range.
This means the audio slider in higan's audio settings panel will start
clamping twice as quickly. So ultimately, we need to figure out how to
fix the centering. This isn't as simple as just subtracting less. We
will probably have to center every individual audio channel before
summing them to do this properly.
Results:
On the Mega Drive, Altered Beast sounds quite a bit better, a lot less
distortion now. But it's still not perfect, especially sound effects.
Further, Bare Knuckle / Streets of Rage still has really bad sound
effects. It looks like I broke something in Cydrak's code when trying to
adapt it to my style =(
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Tim Allen
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fdc41611cf |
Update to v098r14 release.
byuu says:
Changelog:
- improved attenuation of biquad filter by computing butterworth Q
coefficients correctly (instead of using the same constant)
- adding 1e-25 to each input sample into the biquad filters to try and
prevent denormalization
- updated normalization from [0.0 to 1.0] to [-1.0 to +1.0]; volume/reverb
happen in floating-point mode now
- good amount of work to make the base Emulator::Audio support any number
of output channels
- so that we don't have to do separate work on left/right channels;
and can instead share the code for each channel
- Emulator::Interface::audioSample(int16 left, int16 right); changed to:
- Emulator::Interface::audioSample(double* samples, uint channels);
- samples are normalized [-1.0 to +1.0]
- for now at least, channels will be the value given to
Emulator::Audio::reset()
- fixed GUI crash on startup when audio driver is set to None
I'm probably going to be updating ruby to accept normalized doubles as
well; but I'm not sure if I will try and support anything other 2-channel
audio output. It'll depend on how easy it is to do so; perhaps it'll be
a per-driver setting.
The denormalization thing is fierce. If that happens, it drops the
emulator framerate from 220fps to about 20fps for Game Boy emulation. And
that happens basically whenever audio output is silent. I'm probably
also going to make a nall/denormal.hpp file at some point with
platform-specific functionality to set the CPU state to "denormals as
zero" where applicable. I'll still add the 1e-25 offset (inaudible)
as another fallback.
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Tim Allen
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839813d0f1 |
Update to v098r13 release.
byuu says: Changelog: - nall/dsp returns with new iir/biquad.hpp and resampler/cubic.hpp files - nall/queue.hpp added (simple ring buffer ... nall/vector wouldn't cause too many moves with FIFO) - audio streams now only buffer 20ms; so even if multiple audio streams desync, latency can never exceed 20ms - replaced blackman windwed sinc FIR hermite audio filter with transposed direct form II biquadratic sixth-order IIR butterworth filter (better attenuation of frequencies above 20KHz, faster, no need for decimation, less code) - put in experimental eight-tap echo filter (a lot better than what I had before, but still rather weak) - substantial cleanups to the SuperFX GSU processor core (slightly faster, 479KB->100KB object file, 42.7KB->33.4KB source code size, way less code duplication) We'll definitely want to test the whole SuperFX library (not many games) just to make sure there's no regressions caused by this one. Not sure what I want to do with audio processing effects yet. I've always really wanted lots of fun controls to customize audio, and now finally with this new biquad filter, I can finally start implementing real effects. For instance, an equalizer wouldn't be too complicated anymore. The new reverb effect is still a poor man's version. I need to find human readable source for implementing a comb-filter properly. I'm pretty sure I can already treat nall::queue as an all-pass filter since all that does is phase shift (fancy audio term for "delay audio"). What's really going to be hard is figuring out how to expose user-friendly settings for controlling it. It looks like you need a bunch of coprime coefficients, and I don't think casual users are going to be able to hand-enter coprime values to get the echo effect they want. I uh ... don't even know how to calculate coprime values dynamically right now >_> But we're going to have to, as they are correlated to the output sampling rate. We'll definitely want to make some audio profiles so that users can quickly select pre-configured themes that sound nice, but expose the underlying coefficients so that they can tweak stuff to their liking. This isn't just about higan, this is about me trying to learn digital signal processing, so please don't be too upset about feature creep or anything on this. Anyway ... I'm having some difficulties with my audio right now. When the reverb effect is enabled, there's a bunch of static on system reset for just a moment. But this should not be possible. nall::queue is initializing all previous reverb sample elements to 0.0. I don't understand where static is coming in from. Further, we have the same issue with both the windowed sinc and the biquad filters ... a bit of a popping sound when starting a game. Any help tracking this down would be appreciated. There's also one really annoying issue ... I can't seem to do reverb or volume adjustments with normalized samples. If I say "volume *= 0.5" in higan/audio/audio.cpp line 68, it doesn't just halve the volume, it adds a whole bunch of distortion. This makes absolutely zero sense to me. The sample values are between 0.0 (mute) and 1.0 (full volume) here, so multiplying a double by 0.5 shouldn't cause distortion. So right now, I'm doing these adjustments with less precision after denormalizing back to int16. Anyone ever see something like that? :/ |
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Tim Allen
|
0955295475 |
Update to v098r08 release.
byuu says: Changelog: - nall/vector rewritten from scratch - higan/audio uses nall/vector instead of raw pointers - higan/sfc/coprocessor/sdd1 updated with new research information - ruby/video/glx and ruby/video/glx2: fuck salt glXSwapIntervalEXT! The big change here is definitely nall/vector. The Windows, OS X and Qt ports won't compile until you change some first/last strings to left/right, but GTK will compile. I'd be really grateful if anyone could stress-test nall/vector. Pretty much everything I do relies on this class. If we introduce a bug, the worst case scenario is my entire SFC game dump database gets corrupted, or the byuu.org server gets compromised. So it's really critical that we test the hell out of this right now. The S-DD1 changes mean you need to update your installation of icarus again. Also, even though the Lunar FMV never really worked on the accuracy core anyway (it didn't initialize the PPU properly), it really won't work now that we emulate the hard-limit of 16MiB for S-DD1 games. |
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Tim Allen
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7cdae5195a |
Update to v098r07 release.
byuu says: Changelog: - GB: support modeSelect and RAM for MBC1M (Momotarou Collection) - audio: implemented native resampling support into Emulator::Stream - audio: removed nall::DSP completely Unfortunately, the new resampler didn't turn out quite as fast as I had hoped. The final hermite resampling added some overhead; and I had to bump up the kernel count to 500 from 400 to get the buzzing to go away on my main PC. I think that's due to it running at 48000hz output instead of 44100hz output, maybe? Compared to Ryphecha's: (NES) Mega Man 2: 167fps -> 166fps (GB) Mega Man II: 224fps -> 200fps (WSC) Riviera: 143fps -> 151fps Odd that the WS/WSC ends up faster while the DMG/CGB ends up slower. But this knocks 922 lines down to 146 lines. The only files left in all of higan not written (or rewritten) by me are ruby/xaudio2.h and libco/ppc.c |