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ready.
Registered: Feb 2003
Posts: 441 |
SID A/D conversion (POT-X, POT-Y)
Hi everybody,
I'd like to find some information about the proper usage of the analog inputs of the SID. I'm trying to do some audio acquisition for CD, microphone, ect. into the pot-x pot-y inputs of the SID. Do I need any special hardware between the audio source and the SID input (joystick port pin 5 and pin 9)?
thanx,
Ready. |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
The SID A/D converters are too slow for audio sampling. |
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Oswald
Registered: Apr 2002
Posts: 5086 |
some more info on what u want to achieve would help. ATMO it sounds like you want to digitize sounds for a CD with sid. |
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ready.
Registered: Feb 2003
Posts: 441 |
Yes, my first scope was to attach a microphone to the A/D converter, but a microphone signal was too weak and I didn't have an amplifier ready to be used. So I attached the output of a radio (headphone output)into the SID A/D converter, using the following rountine:
LDA #$FF
STA $D406
STA $D406+7
STA $D406+14
LDA #$49
STA $D404
STA $D404+7
STA $D404+14
here
lda $d41a ; A/D input value
lsr lsr lsr lsr
sta $d418 ;volume value
jmp here
After adjusting the radio volume, I managed to have a replay of the input sound, but it was quite crappy. I wonder if it is crappy because of the routine or because of the A/D input converting too slowly.
How did the digitalizers for C64 worked back in the 80s? What C64 input did they use?
thanx,
Ready. |
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Scout
Registered: Dec 2002
Posts: 1570 |
here
lda $d41a ; A/D input value
lsr
lsr
lsr
lsr
sta $d418 ;volume value
jmp here
shouldn't it be:
here
lda $d41a ; A/D input value
sta temp
lsr
lsr
lsr
lsr
sta $d418 ;volume value
ldx #$<some delayvalue>
dex
bne *-1
temp = *+1
lda #$00
and #$0f
sta $d418
jmp here
Quote:
How did the digitalizers for C64 worked back in the 80s? What C64 input did they use?
Digitalizers? Samplers!
You had to stick 'em in your userport so far as I know they didn't use the SID as a A/D converter.
EDIT:
Disabling IRQ's (SEI) and turning off the screen (using $d011...duh!) improves sample replay. |
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ready.
Registered: Feb 2003
Posts: 441 |
Thanx Scout,
I guess that the bad quality of the samples I acquired is only due to the slowness of the SID A/D converters.
Ready. |
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Style
Registered: Jun 2004
Posts: 498 |
samplers used their own ADC chips and were connected via userport, cart port or sometimes even the joystick ports (I had a covox voice master that did that).
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ready.
Registered: Feb 2003
Posts: 441 |
mmmh, joy port....and what pin did they use?
Ready. |
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Raf
Registered: Nov 2003
Posts: 343 |
joy port allows just to read na incoming nibble - that's all you need for C64 sampler :)
www.vulture.c64.org |
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Mace
Registered: May 2002
Posts: 1799 |
Quote:
here
lda $d41a ; A/D input value
sta temp
lsr
lsr
lsr
lsr
sta $d418 ;volume value
ldx #$<some delayvalue>
dex
bne *-1
temp = *+1
lda #$00
and #$0f
sta $d418
jmp here
The STA TEMP and AND#$0F is useless when reading $D41A, as $D41A holds a value between 0 and 255 and not a double nibble of a 'compressed' sample. |
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Scout
Registered: Dec 2002
Posts: 1570 |
Ah! Handy to know that...! |
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ready.
Registered: Feb 2003
Posts: 441 |
@Raf: are you sure about reading a nibble? As far as I know using the pot-x / pot-y, the SID converts a 0-5 V signal into 0-255 digital value (8-bit).
Anyhow, my doubt is how did samplers based on the SID A/D converters (joyport inputs) manage to do a decent sampling? From my experiments I get quite crappy results, caused by (I suppose) the slowness of the A/D conversion. |
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algorithm
Registered: May 2002
Posts: 705 |
Better to sample on something like a PC, resample, process and then place on the c64. |
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chatGPZ
Registered: Dec 2001
Posts: 11352 |
Quote:Anyhow, my doubt is how did samplers based on the SID A/D converters (joyport inputs) manage to do a decent sampling? From my experiments I get quite crappy results, caused by (I suppose) the slowness of the A/D conversion.
there were no samplers that used the sid a/d converters, because like you said, they are too slow. |
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Raf
Registered: Nov 2003
Posts: 343 |
Quote: @Raf: are you sure about reading a nibble? As far as I know using the pot-x / pot-y, the SID converts a 0-5 V signal into 0-255 digital value (8-bit).
Anyhow, my doubt is how did samplers based on the SID A/D converters (joyport inputs) manage to do a decent sampling? From my experiments I get quite crappy results, caused by (I suppose) the slowness of the A/D conversion.
I mean there are 5 data lines connected to joyport. there is even something like fake hrdsid driver - PC connected with C64 by LPT to joyport cable.
www.vulture.c64.org |
