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oziphantom
Registered: Oct 2014
Posts: 478 |
SID POP
Is there anything other than changing the volume that causes the SID to pop?
I'm playing a digi, and then after a while Goattracker kicks back in, and with it a pop. The Digi leaves the Volume register with $1f in it, GT then sets it to $0F.
The SID is configured for Digi as follows :
7271 .2e49 a9 00 lda #$00 lda #$00
7272 .2e4b 8d 05 d4 sta $d405 sta SID+$05 ; voice 1 ad
7273 .2e4e 8d 0c d4 sta $d40c sta SID+$0C ; voice 2 ad
7274 .2e51 8d 13 d4 sta $d413 sta SID+$13 ; voice 3 ad
7275 .2e54 8d 15 d4 sta $d415 sta SID+$15 ; filter lo
7276 .2e57 a9 f0 lda #$f0 lda #$f0
7277 .2e59 8d 06 d4 sta $d406 sta SID+$06 ; sr
7278 .2e5c 8d 0d d4 sta $d40d sta SID+$0D ; sr
7279 .2e5f 8d 14 d4 sta $d414 sta SID+$14 ; sr
7280 .2e62 a9 01 lda #$01 lda #$01
7281 .2e64 8d 04 d4 sta $d404 sta SID+$04 ; ctrl
7282 .2e67 8d 0b d4 sta $d40b sta SID+$0B ; ctrl
7283 .2e6a 8d 12 d4 sta $d412 sta SID+$12 ; ctrl
7284 .2e6d a9 10 lda #$10 lda #$10
7285 .2e6f 8d 16 d4 sta $d416 sta SID+$16 ; filter hi
7286 .2e72 a9 f7 lda #$f7 lda #%11110111
7287 .2e74 8d 17 d4 sta $d417 sta SID+$17 ; filter voices+reso |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
Quote:The Digi leaves the Volume register with $1f in it, GT then sets it to $0F
so change that? there is not much else you can do |
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oziphantom
Registered: Oct 2014
Posts: 478 |
turning off the filter causes it to pop? |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
yes, changing the filter setup generally does that |
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oziphantom
Registered: Oct 2014
Posts: 478 |
I changed the data to
.byte $17,$18,$16,$16,$17,$16,$18,$17,$18,$19,$0a,$0b,$0c,$0d,$0e,$0f
still pops... |
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Knut Clausen
Registered: Apr 2013
Posts: 18 |
Try resetting the SID:
resetting the SID
I don't know much about this, but this has solved sid noise when trying to restart a tune after digi for me earlier. |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
what i did in the past to avoid it is: use $x8 for volume of the SID tune. and then make sure the last value of the sample is also $x8 (or 7) |
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Mixer
Registered: Apr 2008
Posts: 422 |
Sudden output level change causes pop. When the filter is turned on it reverses the output signal from positive to negative initially causing it to pop, and vice versa when turning filter off.
I do not exactly know what happens when filter type is changed, it causes a pop too, perhaps there is some charge in the capacitors or something.
So, in theory, the output level should be at zero when filter is turned on/off or type changed.
Try: lda #$0f sta d418 lda #$00 sta $d418 lda #$1f sta $d418. if it makes any difference. If yes, theory is good, if no, theory is bad.:)
Then there is using filter during digi-play, which is another case altogether. |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
Quote:lda #$0f sta d418 lda #$00 sta $d418 lda #$1f sta $d418
that will also cause a pop, a loud one even :)
if you are really really REALLY desperate to have no audible pop at all, you must change the volume by one every 2 or 3 frames, ie ramp it up (or down) very slowly |
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Mixer
Registered: Apr 2008
Posts: 422 |
Quote: Quote:lda #$0f sta d418 lda #$00 sta $d418 lda #$1f sta $d418
that will also cause a pop, a loud one even :)
if you are really really REALLY desperate to have no audible pop at all, you must change the volume by one every 2 or 3 frames, ie ramp it up (or down) very slowly
I did not expect that the ramp must be that slow, but I guess that makes sense. Hide the snap in the kick drum. |
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chatGPZ
Registered: Dec 2001
Posts: 11108 |
it must be slow so you dont get a "sample"... ie change it once per frame -> you get a 50Hz buzz |
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Oswald
Registered: Apr 2002
Posts: 5017 |
I thought this topic is about SID music in POP style :) |
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tlr
Registered: Sep 2003
Posts: 1714 |
Quote: I thought this topic is about SID music in POP style :)
...when it really was in involuntary glitch-style! ;) |
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Hein
Registered: Apr 2004
Posts: 933 |
You can play your digi without filter, if your tune doesn't use filter at all. But that's not mentioned, so just guessing. |
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oziphantom
Registered: Oct 2014
Posts: 478 |
I turned the filter off at the end of the digi, the pop didn't move, so the filter is not the issue. I will need to trace out the SID writes after the digi stops, and the make a nice test program that sets the values and see if I can track which write causes the pop.. if its not some "just so happens to happen when the some internal state is dead on X" kind of deals. |
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Frantic
Registered: Mar 2003
Posts: 1627 |
If someone investigates SID pops related to the filter in more detail, I'd be very interested to hear about it. |
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Pex Mahoney Tufvesson
Registered: Sep 2003
Posts: 50 |
As Mixer said, the old SID chip pops, mostly due to internal "idle" voltages not being anything near zero. So for 6581, yes, it will pop. The main source for this is that the amplification factor of the filter is negative. So, turning the filter on or off ($d418 from #$1f -> #$0f) will result in a relatively large jump in the DC-offset.
On 8580 this is way more subtle. But it's there.
I did investigate this for sample-playing purposes, and the long version of that can be read here:
https://livet.se/mahoney/c64-files/Musik_RunStop_Technical_Deta..
This has been used in quite a number of demos since then. The first one was Musik Run/Stop
and one of the latest ones was C=Bit 18
There can of course be more sources for popping sounds from the SID than (ab-)using the filter/volume register. If you do find any, please tell! / Pex
---
Have a noise night!
https://livet.se/mahoney |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
Well, I don't know the real hw audio difference, but,
if you don't use voice 3 it's also possible to use:
LDA #$00
STA $D418
and
DEC $D418
INC $D418
This causes all 3 filters on and off + volume 0 to F + voice 3 cut off on/off in one shot. |
