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.
Nov 15, 1984