ChanServ changed the topic of ##yamahasynths to: Channel dedicated to questions and discussion of Yamaha FM Synthesizer internals and corresponding REing. Discussion of synthesis methods similar to the Yamaha line of chips, Sound Blasters + clones, PCM chips like RF5C68, and CD theory of operation are also on-topic. Channel logs: https://freenode.irclog.whitequark.org/~h~yamahasynths
<cr1901_modern>
I would immediately take out the drive and start running scalpel or photorec before you do any more dama- *sees tweets* ... I'm... gonna let you blow off steam first :o
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<andlabs>
also if I do write my vgm player again I'll do so with copyright clearance so I can actually release it
<cr1901_modern>
At least you don't work for Apple
<andlabs>
but that's an if
<Lord_Nightmare>
myon98: I'm back. what exactly is wrong with the current emulation of OPNA's ADPCM?
<Lord_Nightmare>
do you have hardware recordings of samples which play back on the OPNA's external ADPCM mode incorrectly on emulation vs hardware? if so, i'd REALLY love to see those samples and the hardware recordings
<superctr>
the only problem that i have heard is that real hardware has a lot more clicking/popping vs emulation
<superctr>
especially when samples are started and stopped (reset flag is set)
<superctr>
if the ADPCM algorithm itself was bad, then all samples that were generated would eventually degrade into noise or DC offsets when played back on real HW
<Lord_Nightmare>
the adpcm algorithm isn't terrible
<Lord_Nightmare>
the problem is there's two nearly identical algorithms that could be used, and i'm not sure which of the two is actually used
<superctr>
i know for sure it's not the AICA/YMZ algorithm
<superctr>
the algorithm currently used is good, the easiest way to verify that is to simply encode a sample and play it back on real hardware (since ADPCM uses the same algorithm for encoding and decoding)
<superctr>
My ADPCM encoder is used in BambooTracker and it has been verified on real HW
<Lord_Nightmare>
but i thought the AICA algorithm is actually slightly different (saturates at a different stage?) than the older yamaha chips do
<Lord_Nightmare>
unless that information is wrong
<superctr>
well, i'm saying that the 2608 does not use that algorithm
<superctr>
the step table is different and the saturation is different. And the nibbles are swapped
<kode54>
funny thing
<kode54>
I fixed the AICA thing based on Yamaha's own encoder behavior
<kode54>
and it broke some other game that didn't observe that saturation behavior
<kode54>
fixed Shenmue saturating into DC offset hell, though
<andlabs>
sorry for the noise, I guess
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<myon98>
My experience was from fmgen and mame emulation, I thought that the hardward decoding is done in a lower quality way than the vague description in the datasheet so I tried to compare their spectrums and try to guess how it was different (samplerate, interpolation)
<myon98>
But ultimately as my YM2608 digital output capture circuit didn't work with ADPCM DRAM soldered on I gave up at that time and just hoped to go through YM2610 die photo
<myon98>
superctr I didn't realize that there is an ADPCM decoder that was tested against real hardware, sorry for my ignorance
<myon98>
I will to look into the source code of it
<superctr>
from what i have heard it is possible that there is a low pass filter done on the *decoded* samples
<superctr>
but i can't tell if it's done within the chip or outside the chip. if it's within the chip, you should use "Yamaha's transitor razor" and it likely to be just a simple first order filter with the cutoff function simply being a right shift
<myon98>
What do you mean by "Yamaha's transistor razor"? I'm interested
<superctr>
the solution requiring the smallest numbers of transistors is the most likely
<superctr>
I heard it from TITAN's megadrive docs :P
<myon98>
Oh now I see
<myon98>
I've also felt that way when they didn't include a register to save the accumulated sample to adjust the accumulation period between LR channels
<myon98>
Although I really love the consequences of it