03726: popeye: Discrete sound filter for AY-3-8910 voice A not emulated

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
03726	Sound	Minor	Always	Feb 10, 2010, 11:36	Feb 4, 2014, 12:12

Tester	Oliver_A	View Status	Public	Platform
Assigned To	AWJ	Resolution	Fixed	OS
Status [?]	Resolved			Driver	nintendo/popeye.cpp
Version	0.136u2	Fixed in Version	0.153	Build
		Fixed in Git Commit		Github Pull Request #

Summary	03726: popeye: Discrete sound filter for AY-3-8910 voice A not emulated
Description	On the original Popeye board, sound channel A from AY-3-8910 is run through a discrete filter, producing a smoothed wave form. On MAME, the channel is reproduced without filtering, resulting in a harsher square wave sound. Note: this only affects sound channel A.
Steps To Reproduce	Turn on your original Popeye machine, and listen to the title melody. You'll notice that the 2 channels playing the leading melody sound sharp, but the channel playing the backgound beat is much more smooth and not a square wave. Start the game, hear the introduction music, same pattern: leading melody is a sharp square wave, background beat is smooth. Now play the game. All sound effects are sharp square waves. The background melody however is smooth. See also Popeye schematics sheet 2, upper right corner. When I am taking the sound directly at resistor R52, bypassing the whole circuit, voice A is sounding as sharp as wrongly emulated in MAME. Probable cause for filtered sound: capacitor C4, 0.047uF, resistor R51, 20KOhm Circuit has been verified with original board. See picture for circuit.
Additional Information	I am going to provide some sound samples during the day. EDIT: Sample has been uploaded. EDIT: Part of schematic has been uploaded.
Github Commit

Flags	Verified with Original
Regression Version
Affected Sets / Systems	popeye

Attached Files	popeye_sound.mp3 (1,125,982 bytes) Feb 10, 2010, 12:46
Attached Files	popeye_sound.jpg (76,187 bytes) Feb 10, 2010, 13:21

No.05686 Tafoid Administrator Feb 10, 2010, 12:31	Suffice it to say, there are probably hundreds of games that have yet to get such filtering involving the ay8910/ym2149. It's been a slow process of adding them. I can acknowledge this for now, but not sure when those who deal with discrete issues can apply any fix. Reference recordings and examples are good, however, and will facilitate the process.
No.05687 Oliver_A Tester Feb 10, 2010, 12:48 edited on: Feb 10, 2010, 13:24	I have now uploaded a whole sound section. If someone wants to implement it, he/she can listen to this sound file and look at the schematics. The filtering seems to be caused by capacitor C4.
No.05688 Fujix Administrator Feb 10, 2010, 13:06	Thanks for uploading the original sound. I set the report status Confirmed.
No.06055 couriersud Developer May 7, 2010, 21:30	The schematics could be emulated using 3 RC filters and a discrete mixer in MAME.
No.10235 AWJ Developer Feb 4, 2014, 12:12	I've hooked up an RC filter matching the schematic to the first AY channel. The caps on the other two channels are only 330pF; the amount of lowpass filtering they provide is probably outside the range of human hearing and certainly outside the precision of the old integer-based flt_rc device.