Editing POKEY (section)

===Audio Channel Control===

The Audio Channel control registers provide volume and distortion control over individual sound channels. Audio may also be generated independently of the POKEY clock by direct volume manipulation of a sound channel which is useful for playing back digital samples.

====AUDC1 $D201 Write====
Audio Channel 1 Control

====AUDC2 $D203 Write====
Audio Channel 2 Control

====AUDC3 $D205 Write====
Audio Channel 3 Control

====AUDC4 $D207 Write====
Audio Channel 4 Control

{| class="wikitable"
|-
! Bit 7 !! Bit 6 !! Bit 5 !! Bit 4 !! Bit 3 !! Bit 2 !! Bit 1 !! Bit 0
|-
| Noise 2 || Noise 1 || Noise 0 || Force Volume || Volume 3 || Volume 2 || Volume 1 || Volume 0 
|}

Bit 0-3: Control over volume level, from 0 to F.

Bit 4: Forced volume-only output. When this bit is set the channel ignores the AUDF timer, noise/distortion controls, and high-pass filter. Sound is produced only by setting volume bits 0:3 . This feature was used to create digital audio via [[pulse-code modulation]].

Bit 5-7: Shift register settings for noises/distortion. Bit values described below:

{| class="wikitable"
|-
! Noise Value !! Bits Value !! Description
|-
| 0 0 0 ||  $00 || 5-bit then 17-bit polynomials
|-
| 0 0 1 ||  $20 || 5-bit poly only
|-
| 0 1 0 ||  $40 || 5-bit then 4-bit polys
|-
| 0 1 1 ||  $60 || 5-bit poly only
|-
| 1 0 0 ||  $80 || 17-bit poly only
|-
| 1 0 1 ||  $A0 || no poly (pure tone)
|-
| 1 1 0 ||  $C0 || 4-bit poly only
|-
| 1 1 1 ||  $E0 || no poly (pure tone)
|}

Generating random noises is served by reading 8 bits from top of 17-bit shift register. That registers are driven by frequency 1.79&nbsp;MHz for NTSC or 1.77&nbsp;MHz for PAL. Its outputs can by used independently by each audio channels' divider rate.