somewhat improved system descriptions

papers/doc/7-systems/ay8910.md

@@ -1,8 +1,8 @@
 # General Instrument AY-3-8910
 
-this chip was used in several home computers (ZX Spectrum, MSX, Amstrad CPC, Atari ST, etc.), video game consoles (Intellivision and Vectrex), arcade boards and even slot machines!
+this chip was used in many home computers (ZX Spectrum, MSX, Amstrad CPC, Atari ST, etc.), video game consoles (Intellivision and Vectrex), arcade boards and even slot machines!
 
-the chip's powerful sound comes from the envelope...
+It is a 3-channel PSG sound source. The chip's powerful sound comes from the envelope...
 
 AY-3-8914 variant was used in Intellivision, it's basically original AY with 4 level envelope volume per channel and different register format.
 
@@ -39,4 +39,4 @@ AY-3-8914 variant was used in Intellivision, it's basically original AY with 4 l
   - in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
   - `x` is the numerator.
   - `y` is the denominator.
-  - if `x` or `y` are 0 this will disable auto-envelope mode.
+  - if `x` or `y` are 0 this will disable auto-envelope mode.

papers/doc/7-systems/nes.md

@@ -2,7 +2,7 @@
 
 the console from Nintendo that plays Super Mario Bros. and helped revive the agonizing video game market in the US during mid-80s.
 
-also known as Famicom.
+also known as Famicom. It is a five-channel PSG: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and  fifth is a (D)PCM sample channel
 
 # effects
 
@@ -15,4 +15,4 @@ also known as Famicom.
 - `14xy`: setup sweep down.
   - `x` is the time.
   - `y` is the shift.
-  - set to 0 to disable it.
+  - set to 0 to disable it.

papers/doc/7-systems/opl.md

@@ -5,15 +5,14 @@ a series of FM sound chips which were very popular in DOS land. it was so popula
 essentially a downgraded version of Yamaha's other FM chips, with only 2 operators per channel.
 however, it also had a drums mode, and later chips in the series added more waveforms (than just the typical sine) and even a 4-operator mode.
 
-the original OPL was present as an expansion for the Commodore 64 and MSX computers (erm, a variant of it). it only had 9 channels and drums mode.
+the original OPL (Yamaha YM3526) was present as an expansion for the Commodore 64 and MSX computers (erm, a variant of it). it only had 9 two-operator channels and drums mode.
 
-its successor, the OPL2, added 3 more waveforms and was one of the more popular chips because it was present on the AdLib card for PC.
+its successor, the OPL2 (Yamaha YM3812), added 3 more waveforms and was one of the more popular chips because it was present on the AdLib card for PC.
 later Creative would borrow the chip to make the Sound Blaster, and totally destroyed AdLib's dominance.
 
-the OPL3 added 9 more channels, 4 more waveforms, 4-operator mode (pairing up to 12 channels to make up to six 4-operator channels), quadraphonic output (sadly Furnace only supports stereo) and some other things.
-it was overkill.
+the OPL3 (Yamaha YMF262) added 9 more channels, 4 more waveforms, rudimentary 4-operator mode (pairing up to 12 channels to make up to six 4-operator channels), quadraphonic output (sadly Furnace only supports stereo) and some other things.
 
-afterwards everyone moved to Windows and software mixing...
+afterwards everyone moved to Windows and software mixed PCM streaming...
 
 # effects
 

papers/doc/7-systems/opll.md

@@ -1,6 +1,6 @@
 # Yamaha YM2413/OPLL
 
-the YM2413, otherwise known as OPLL, is a cost-reduced FM synthesis sound chip manufactured by Yamaha Corporation and based on the Yamaha YM3812 sound chip (OPL2). thought OPL was downgraded enough? :p
+the YM2413, otherwise known as OPLL, is a cost-reduced FM synthesis sound chip, based on the Yamaha YM3812 (OPL2). thought OPL was downgraded enough? :p
 
 # technical specifications
 

papers/doc/7-systems/pce.md

@@ -1,9 +1,11 @@
 # PC Engine/TurboGrafx-16
 
-a console from NEC that attempted to enter the fierce battle between Nintendo and Sega, but because its capabilities are a mix of third and fourth generation, it failed to last long.
+a console from NEC that, depending on a region:
+ attempted to enter the fierce battle between Nintendo and Sega, but because its capabilities are a mix of third and fourth generation, it failed to last long. (US and Europe)
+ was Nintendo's most fearsome rival, completely defeating Sega Mega Drive and defending itself against Super Famicom (Japan)
 
 it has 6 wavetable channels and the last two ones also double as noise channels.
-furthermore, it has some PCM!
+furthermore, it has some PCM and LFO!
 
 # effects
 

papers/doc/7-systems/pcspkr.md

@@ -1,6 +1,6 @@
 # PC Speaker
 
-40 years of one square beep - and still going!
+40 years of one square beep - and still going! Single channel, no volume control...
 
 # effects
 

papers/doc/7-systems/sms.md

@@ -2,7 +2,7 @@
 
 the predecessor to Genesis.
 
-surely had better graphics than NES, but its sound is subject of several jokes.
+surely had better graphics than NES, but its sound (fairly weak, 4ch PSG with A-3 is a lowest tone) is subject of several jokes.
 
 this console is powered by a derivative of the Texas Instruments SN76489.
 

papers/doc/7-systems/wonderswan.md

@@ -1,11 +1,8 @@
 # WonderSwan
 
-A handheld console released only in Japan by Bandai. Designed by the same
-people behind Game Boy and Virtual Boy, it has lots of similar elements from
-those two systems in the sound department.
+A handheld console released only in Japan by Bandai. Designed by the same people behind Game Boy and Virtual Boy, it has lots of similar elements from those two systems in the sound department.
 
-It has 4 wavetable channels, one channel could play PCM, the other has hardware
-sweep and the other could play noise.
+It has 4 wavetable channels, channel #2 could play PCM, channel #3 has hardware sweep and channel #4 could play noise.
 
 # effects
 

papers/doc/7-systems/ym2151.md

@@ -1,6 +1,6 @@
 # Yamaha YM2151
 
-the sound chip powering several arcade boards and the Sharp X1/X68000.
+the sound chip powering several arcade boards and the Sharp X1/X68000. Eight 4-op FM channels, with overpowered LFO and almost unused noise generator.
 
 it also was present on several pinball machines and synthesizers of the era, and later surpassed by the YM2414 (OPZ) present in the world-famous TX81Z.
 

papers/doc/7-systems/ym2610.md

@@ -2,7 +2,7 @@
 
 originally an arcade board, but SNK shortly adapted it to a rather expensive video game console with the world's biggest cartridges because some people liked the system so much they wanted a home version of it.
 
-its soundchip is a 3-in-1: FM, YM2149 (AY-3-8910 clone) and 2 different format ADPCM in a single package!
+its soundchip is a 4-in-1: 4ch 4-op FM, YM2149 (AY-3-8910 clone) and 2 different format ADPCM in a single package!
 
 # effects
 
@@ -56,4 +56,4 @@ its soundchip is a 3-in-1: FM, YM2149 (AY-3-8910 clone) and 2 different format A
   - in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
   - `x` is the numerator.
   - `y` is the denominator.
-  - if `x` or `y` are 0 this will disable auto-envelope mode.
+  - if `x` or `y` are 0 this will disable auto-envelope mode.

papers/doc/7-systems/ym2612.md

@@ -1,6 +1,6 @@
 # Yamaha YM2612
 
-one of two chips that powered the Sega Genesis.
+one of two chips that powered the Sega Genesis. It is a six-channel, four-operator FM synthesizer. Channel #6 can be turned into 8-bit PCM player.
 
 # effects