Re: [hatari-devel] New cycle exact YM2149 emulation

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I just took a quick look at all of the few code changes (large research)
that make this big improvement. Excellent.

----- Nicolas Pomarède wrote:
> Hi
> after extensive tests on my STF to measure as accurately as possible 
> some not well documented behaviours of the YM2149, I wrote a new 
> rendering for sound emulation.
> The YM2149 works at 2 MHz, but all internal counters (tone, noise, 
> envelope) are handled using a 250 kHz clock.
> By measuring my STF output, I could also confirm that all counters are 
> incremented from '0' up to 'period' (and no the opposite as stated in 
> Yamaha documentation)
> The YM2149 emulation now does the same, all internal counters are 
> incremented 250000 per second and the resulting state is used to output 
> new audio data at the host frequency (for example 44.1 kHz)
> This allows to accurately emulate some very specific tone transitions, 
> as well as some random "phase cancelling" effects (as reported by Troed 
> in some 7an musics), but overall it's safe to say that 95% or more of 
> all musics were already correctly emulated and will sound the same.
> For now, the code in sound.c uses a "#define YM_250" to enable this new 
> rendering ; it can be commented to use the previous method in case some 
> regressions would be reported.
> For now, I think this gives Hatari the most accurate YM2149 emulation of 
> all emulators :)
> Next step will be to improve the filters, as it seems the sound is too 
> "attenuated" in many case. I will capture some real music wav recording 
> to be able to compare with Hatari output and see where and how it could 
> be improved.
> Nicolas

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