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TWW
Registered: Jul 2009
Posts: 545 |
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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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: 545 |
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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TWW
Registered: Jul 2009
Posts: 545 |
Alright. I guess that's sorted then :)
Thanx to all involved and taking the time to reply! |
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ready.
Registered: Feb 2003
Posts: 441 |
but back to the original problem of not hearing the SID when $d418 = 0. Is it really a problem? I haven't tested but the zero would be played for just a very short period of time (sampling time), and would hardly be noticable. |
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TWW
Registered: Jul 2009
Posts: 545 |
If I understood you correctly;
The point of doing 3 bit samples is that you can have the 4th bit (bit #3) set at all times, thus making any sound produced by the SID hearble even though you use the 3 LSBs (bit 0, 1 & 2) to modulate samples. This will effectivly give you 3 sid voices + 1 "3 bit sample voice". i.e. $d418 would never be zero but instead range from 8 to 15 depending on sampledata.
If I didn't understand you correctly: What? |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
that idea is somewhat broken, what you really should do is simply use 4 bit samples and be done with it, there is no need to sacrifice that one bit at all. |
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TWW
Registered: Jul 2009
Posts: 545 |
Alright. I'll do some testing on the whole matter and see what I come up with. I do however see ready.'s point of $d418 being 0 during sample playing but then again how much does it matter?
Let's for the sake of argument say that it is a problem for a sid-tune playing at the same time. with 4 bit samples you could then probably do "lsr + ora #$08" and get away with it (yes this is one thing I'm gonna test soon(tm)).
If this is the case, why not just have the sample in 3 bits to begin with (Maybee even processed a bit better then a straight lsr) and then gain a 25% memory boost in the process?
Or maybee I should just shut up and test it 8-D |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
the point is that the average level of an audio sample is pretty much exactly half its amplitude. so playing a 4 bit sample along a sid tune practically equals playing the sid tune at half volume. now if you reduce the sample to 3 bits and offset it by 8 (by setting bit 3) that will equal playing the sid tune at 75% original volume.
so you are really trying to solve a problem that does not exist, you are only making it worse =) |
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