01066: YM2203 SSG-EG inaccuracy.

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
01066	Sound	Minor	Have not tried	Feb 9, 2008, 08:22	Jun 23, 2021, 07:08

Tester	-Misc Reporters-	View Status	Public	Platform
Assigned To		Resolution	Fixed	OS
Status [?]	Resolved			Driver
Version	0.114u4	Fixed in Version		Build
		Fixed in Git Commit		Github Pull Request #

Summary	01066: YM2203 SSG-EG inaccuracy.
Description	YM2203 SSG-EG inaccuracy: Seems to be emulation of YM2203 feature 'SSG-EG' has inaccuracy in MAME. We (I as programmer and some other people as hardware developers) construct some sort of sound card which uses YM2203, and I wrote software for it. For testing purposes I use some of source code from MAME, related to YM2203 emulation (to make fast tests on PC, instead of real thing). Now listen to two attached samples - which contains short part of music and then all possible SSG-ENV types in one channel. One of these samples recorded from real thing, YM2203 @3.5 MHz, and another rendered by YM2203 emulation code from MAME. Comments in fm.c code said: The difference (when compared to normal Envelope Generator mode) is that the resolution in Decay and Sustain phases is 4 times lower; this results in only 256 steps instead of normal 1024. But seems to resolution in SSG-EG mode 8 times lower, not 4. I checked that by changing adding value from 4 to 8 in strings 1147 and 1170 of fm.c, and it sounds more like true. But there still some differences with envelope stages, by now I can't figure it clearly (you can see this in samples with any audio editor).I also can provide test register array (in simply format, .GYM-like), which was used to record these samples.
Steps To Reproduce
Additional Information	Posted by Shiru
Github Commit

Flags	Verified with Original
Regression Version
Affected Sets / Systems

Attached Files	emulated_ym2203.mp3 (207,376 bytes) Feb 14, 2008, 17:58
Attached Files	real_ym2203.mp3 (245,510 bytes) Feb 14, 2008, 17:58

No.01110 couriersud Developer May 27, 2008, 20:23	The register dump would be much appreciated .... The samples are a good base to start, but the registers would allow easy tracking of code.
No.19024 aaron Developer Jun 23, 2021, 07:07	This is a useless bug report as there is no means of reproducing the problem. Further, the FM engine has been completely rewritten since then. If a similar problem still exists, a new bug should be created with actual repro steps or VGM files so we can isolate the issue.