Editing POKEY (section)

==Audio==
Pokey contains a [[programmable sound generator]]; four audio channels with separate frequency, noise and voice level controls.

Each channel has an 8-bit frequency divider and an 8-bit register to select noise and volume.
*AUDF1 to AUDF4&nbsp;– frequency register (AUDio Frequency)
*AUDC1 to AUDC4&nbsp;– volume and noise register (AUDio Control)
*AUDCTL&nbsp;– general register, which controls generators (AUDio ConTroL)

POKEY's sound is distinctive: when the four channels are used independently, there is noticeable detuning of parts of the 12-tone [[equal temperament]] scale, due to lack of pitch accuracy. Channels may be paired for higher accuracy; in addition, multiple forms of [[distortion]] are available, allowing a thicker sound. The distortion is primarily used in music for bass parts.

===Audio Channel Frequency===

The AUDF* registers control the frequency or pitch of the corresponding sound channels. The AUDF* values also control the POKEY hardware timers useful for code that must run in precise intervals more frequent than the vertical blank.

Each AUDF* register is an 8-bit value providing a countdown timer or divisor for the pulses from the POKEY clock. So, smaller values permit more frequent output of pulses from POKEY, and larger values, less frequent. The values $0<sub>hex</sub>/0<sub>dec</sub> to $FF<sub>hex</sub>/255<sub>dec</sub> are incremented by POKEY to range from $1<sub>hex</sub>/1<sub>dec</sub> to $100<sub>hex</sub>/256<sub>dec</sub>. The actual audible sound pitch is dependent on the POKEY clock frequency and distortion values chosen. See [[POKEY#Audio Channel Control|Audio Channel Control]] and [[POKEY#AUDCTL $D208 Write|Audio Control]].

====AUDF1 $D200 Write====
Audio Channel 1 Frequency

====AUDF2 $D202 Write====
Audio Channel 2 Frequency

====AUDF3 $D204 Write====
Audio Channel 3 Frequency

====AUDF4 $D206 Write====
Audio Channel 4 Frequency

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

===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.

===AUDCTL $D208 Write===

Audio Control allows the choice of clock input used for the audio channels, control over the high-pass filter feature, merging two channels together allowing 16-bit frequency accuracy, selecting a high frequency clock for specific channels, and control over the "randomness" of the polynomial input.

{| class="wikitable"
|-
! Bit 7 !! Bit 6 !! Bit 5 !! Bit 4 !! Bit 3 !! Bit 2 !! Bit 1 !! Bit 0
|-
| 17 vs 9 Poly || CH1 1.79 || CH3 1.79 || CH2 + 1 || CH4 + 3 || FI1 + 3 || FI2 + 4 || 64 vs 15&nbsp;kHz 
|}

"1" means "on", if not described:

;Bit 0: $01: (15&nbsp;kHz), choice of frequency divider rate "0" - 64&nbsp;kHz, "1" - 15&nbsp;kHz
;Bit 1: $02: (FI2 + 4), high-pass filter for channel 2 rated by frequency of channel 4
;Bit 2: $04: (FI1 + 3), high-pass filter for channel 1 rated by frequency of channel 3
;Bit 3: $08: (CH4 + 3), connection of dividers 4+3 to obtain 16-bit accuracy
;Bit 4: $10: (CH2 + 1), connection of dividers 2+1 to obtain 16-bit accuracy
;Bit 5: $20: (CH3 1.79), set channel 3 frequency "0" is 64&nbsp;kHz. "1" is 1.79&nbsp;MHz NTSC or 1.77&nbsp;MHz PAL
;Bit 6: $40: (CH1 1.79), set channel 1 frequency "0" is 64&nbsp;kHz. "1" is 1.79&nbsp;MHz NTSC or 1.77&nbsp;MHz PAL
;Bit 7: $80: (POLY 9), switch shift register "0" - 17-bit, "1"&nbsp;– 9-bit

All frequency dividers (AUDF) can be driven at the same time by 64&nbsp;kHz or 15&nbsp;kHz rate.

Frequency dividers 1 and 3 can be alternately driven by CPU clock (1.79&nbsp;MHz NTSC, 1.77&nbsp;MHz PAL).
Frequency dividers 2 and 4 can be alternately driven by output of dividers 1 and 3.
In this way, POKEY makes possible connecting of 8-bit channels to create sound with 16-bit accuracy.

Possible channel configurations:
* four 8-bit channels
* two 8-bit channels and one 16-bit channel
* two 16-bit channels