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TWW
Registered: Jul 2009
Posts: 541 |
Converting samples to 3 bit
What I want to do:
Play a 3 voice SID tune - while using the 3 LSB's of $d418 to play samples simultaniously (3rd bit of $d418 always set so one always hear the tune).
Problem:
#1: Making samples <- Suggestion for FW/PD tool to make samples with (win7x64).
#2: Converting the sample to 3 bits from however bit-width it was greated from tool in #1 <- The correct mathematical way or a converter to do it.
#3: Any good tip on how to make the samples as "clean" as possible in addition to higher sample frequency? (i.e. any pitfalls I should try to avoid like sampling with too high bit-width or such(which might lead to a bad conversion etc.))? <- Yeah I totally don't know what I'm talking about here in #3 so bear with me 8-D
/TWW |
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TWW
Registered: Jul 2009
Posts: 541 |
@ The Human Code Machine: A LSR would yieald 4 bits so still I'm 1 bit short. But I get your drift. Find the shrinkage factor and do it.
But I came to the same conclusion as you, more then just raw shrinkage (^^) needs to be applied to get a good result.
Has anyone had the chance to try out "Soundslogical Resampler"? It states it can handle various bit-width but ofcourse the demo is screwed. I don't mind dishing out some 20-30 $ (good echange rate anywasy) for it but would like to know if it works first...
@ Ready:
Alright, I got it now 8-D. Sample in "X"kHz but no sounds higher then "X/2"Khz for cleanest sound playback (hence the LP filter). It seems this can be post processed though in the proggie i mentioned above. If not I'll ask again^^ Thanx! |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
why all this complicated stuff ?
soundforge, wavelab, audition - save as 4 bit unsigned raw.
(or save as 8 bit unsigned raw 8000 hz (THE old way)
convert to 3 bit in realtime on c64 with some code.
those programs resample as it shall be done, and so you dont have to do anything of that. |
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ready.
Registered: Feb 2003
Posts: 441 |
@rambones: I am 99% sure most of those programs have automatic functions for "clean" re-sampling (i.e.: built in LP-filter and everything), but I just wanted to point out the theory, just in case TWW or others wanted to do the re-sampling in their own way.
I am working on a sound sampler for user-port and noticed the importance of the LP-filter for getting rid of aliasing noise. |
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The Human Code Machine
Registered: Sep 2005
Posts: 110 |
@TWW For each bit less you'll need one LSR. If you want convert 8 bit samples to 3 bit samples you'll have to LSR 5 times. |
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chatGPZ
Registered: Dec 2001
Posts: 11114 |
and remember to save them as unsigned before, or that shifting stuff will give you something like nu metal =) |
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TWW
Registered: Jul 2009
Posts: 541 |
THCM:
5 LSRs?
8 bit sample gives an unsigned number between 0 to 255
3 bit sample gives an unsigned number between 0 to 7
so if the value = 161 in 8 bit the value in 3 bit should be equevivalent to:
161/255*7 = 4
If you take 161 and do 5 LSRs you get: 5
So I don't think it's entirely accurate to do it this way. I could how ever be terribly wrong here :) (it has happened before^^)
@ rambones: Can you also save in 3 bit? (25% less space right of the bat^^) |
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ready.
Registered: Feb 2003
Posts: 441 |
@TWW: the correct math is:
161/256*8=5
which yelds to 5 times LSR
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TWW
Registered: Jul 2009
Posts: 541 |
Quote: @TWW: the correct math is:
161/256*8=5
which yelds to 5 times LSR
Actually the correct math is:
INT(161/256*8) = 5
If you rely on the rounding it does not work correctly (for some of the values in the byte range).
Anyways, the LSR x 5 is waterproof (yes I was wrong but to my defense I did mention that as a slight posibility^^).
Then the remaining question is:
Is this good enough or would a converter taking into account THCM's suggestion above regarding noise shaping and/or dithering be a (mouch?) better result? |
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ready.
Registered: Feb 2003
Posts: 441 |
I guess the answer can be given by testing several conversion algorithms only. |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
The leading sample programs can only save as 2/4/8/16+ etc.
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