Date: Sat, 5 Apr 1997 03:46:58 -0500 (EST)
To: tghack-list@joyce.eng.yale.edu
From: David Michel <dmichel@easynet.fr>
X-Software: MLF v2.3, Copyright 1995, 1996 by Bt
X-Original-Id: <1.5.4.16.19970405104056.1a1fcc52@mail.easynet.fr>
Subject: Re: PCE Sound
X-UIDL: a57f5a900ee242f1dd51c8397e66dfca


>$0804 - Channel on/dda/volume - voice-dependent register
>               bit 7   = 'on'  - (I believe it's a voice-enable flag)
>               bit 6   = 'dda' - 'Direct digital-to-analogue'(?)  With
>                                 this flag set, any value written into the
>                                 'wave data' location will directly appear
>                                 on the channel's output, rather than be
>                                 stored in the circular wave buffer
>               bit 0-4 = voice volume
>        Mask = $CF

    About the DDA flag, may be it has another function, i'm not
    sure - this is just a guess. In some games, when they load
    a waveform, they do that :

                LDA   #$40
                STA   $0804
                LDA   #$00
                STA   $0804
                LDY   #$00
        LOOP:   LDA   ($F2),Y
                STA   $0806
                INY 
                CPY   #$20
                BNE   LOOP

    I suppose that the internal wave index register is cleared when
    this bit is set or when it pass from '1' to '0'. But may be i'm
    totaly wrong ;)
    
>$0807 - Noise - (voice-dependent register, available only to voices 5 & 6)
>                      bit 7   = noise enable
>                      bit 0-4 = noise frequency (some experimentation
>                                needs to be done, to understand the range
>                                of these values, and their sound)
>        Mask = $9F

    So far i multiply the frequency by 64, and i use it like for
    channels frequency. It sounds approximately correct, but i don't
    have a PC Engine to verify that :(

>The LFO is not a per-voice attribute.
>Unfortunately, I don't know much else about it, or understand how these
>affect sound:
>
>$0808 - LFO Frequency
>        Mask = $FF
>
>$0809 - LFO Control - bit 7   = LFO trigger (?)
>                      bit 0&1 = LFO Control (?)
>        Mask = $83

    Here only experimentations will tell more. Dave, do you have
    made some tests on that with the help of the Develo Box ?
    Just sending random values to see what happens :)

    Bye,
    David

PS. Just some more lines to avoid the 'you quoted more material
    than you added' problem. Sure it's a good idea but sometimes
    it's a bit annoying ;) Why not using a ratio of 10 new lines
    for 15 quoted lines, it would be nicer.