People not involved with audio for System I need not read on:

Brad, with the aid of Sam, Don, Minh and others too numerous to name
have completed the relative balancing of the Pokey, Yamaha and TI Sound
chips and this "balance" has been incorporated into the production
released parts list.  If you have serious concerns about the appropriateness
of this balance after reading the rest of the message, please contact me
or Brad Fuller.

QUESTION:	What do you have to do to make the audio on your board be 
		like production?
ANSWER:		Nothing.
REASON:		All voice cartridges of any REV and 
		TTL Main Boards REV(A) and REV(2) modified to REV(A) 
		(these will have "REV(A)" marked on the edge connector) 
		have the correct component values.  In case you question
		your board the "balance" and proper filter/noise supression
		values are listed at the end of this message.

METHOD OF BALANCING:
		If you are interested in how Brad arrived at this 
		standard, here is what he did.


Adjustment of audio levels for YAMAHA, POKEY and TIVOX for SYSTEM I

"To calculate the initial gain of the YAMAHA chip set and POKEY, we first
produced a full volume sine wave from YAMAHA and a full volume square wave from
POKEY and 'course' adjusted the level for POKEY. Since it's best to use a real
live situation we used PACKRAT music and sound effects to 'fine' set the POKEY
level. We had to compromise on the setting since all music and sound effects
are never at the same level. After the final adjustment we measured the average
output of both chips. The POKEY was at about half the peak amplitude as the
YAMAHA. 

"To adjust the TIVOX chip level we installed a pot to adjust the TIVOX chip
gain. This enabled us to set the TIVOX chip for the level desired, then measure
the resistance at the pot. Since POKEY sounds are usually intermittent sounds
it was best to use the sound source that the TIVOX chip would have to
continually compete against, i.e. YAMAHA music. We used different types and
volumes of music to adjust the TIVOX chip gain. After adjustment of the TIVOX
chip, we realized that it was very close to the original setting calculated by
Don Paauw." 


PROPER CONPONENTS FOR AUDIO BALANCE AS IN REV(A) PRODUCITON RELEASE.
		
		MAIN BOARD--------------------------------------------
		(the problem which is corrected)-
		Pokey noise-
		add C195 1000pf from IC 19E pin 6 to gnd
		Pokey balance-
		R112	1k
		R114	10K
		R70, R74	27k
		Yamaha Balance-	none
		Yamaha noise/filtering
		C166,167	.0027 microfarads
		C99, 100	1000pf
		Aux Audio Balancing and Noise-
		Add R138 1k from AUXSNDR to gnd
		Add R139 1k from AUXSNDL to gnd
		Final audio filtering-
		C175, 176	1000pf
		CART BOARD----------------------------
		no changes

Jed,
	Do you recommend that any action be taken?
Morgan

From:	HOFF           15-NOV-1984 15:50  
To:	MARGOLIN

From:	MARGOLIN       15-NOV-1984 13:28  
To:	HOFF
Subj:	System I Audio Level

As of last week, the maximum audio output level produced by Marble Madness
during game play was 4 Vp-p. The Regulator/Audio III requires 5 Vp-p for 
full output (worst case).

		Jed

I forwarded the message to Sam and asked him to investigate.
also a copy of the message is forwarded to you.
Morgan

From:	MARGOLIN       15-NOV-1984 15:42  
To:	HOFF
Subj:	System I Audio Level

The audio output level should be increased to 5 Vp-p during normal
game play, and should have a reasonable amount of headroom for peaks.

Background:

1. If you leave the output purposefully low so that the audio does not clip 
under any conditions, then most of the time it will not be as loud as it 
could otherwise be.

2. By having the output high enough to clip with the volume control all the
way up you assure that it can be adjusted for maximum loudness.
Presumably the operators will adjust it short of clipping.

3. In the old days, the volume was controlled via a rheostat at the
amplifier output, so that if the amplifier was clipping it could
not be fixed by turning the volume down. The volume control pots
on Regulator/Audio III are at the amplifier input.

4. The amount of dynamic range available for arcade games is fairly narrow.
Arcades tend to be noisy, which sets the low end. The high end is set by the 
amount of audio power reaching the player's ears and is limited by the 
threshhold of pain. Also, if too many sounds are turned on at the same time,
they will simply become an indistinguishable jumble.  

5. Generally, sounds with very high ratios of peak to average levels (like 
explosions) have been allowed to clip. Otherwise, if the system is adjusted
to handle the peaks, the average volume level is too low.