pouët.net

 PMD3-Infotext
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As  I want to release it finally (it seems to be 100% Bug-Free) I think  it 
is important to write some lines about the packer and the format.  So  that 
maybe someone else than me will use it....




I. What is it? 
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PMD3 is my (Dynacore/TSCC) own little patterncompressed moduleformat, which 
allows to depack the module in realtime while playing without (nearly)  any 
loss of CPU-time.

PMD3.PRG for 4-Channel mods and
PMD3_V8.PRG for 8-Channel mods
(Sorry that both are quite slow, but it's pure GfA-Basic code...)



II. What means PMD3?
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This one is called PMD3 (P.acked-M.oD.ule,  Version 3), because this is the 
third change in the DEPACKER-Code.

The  idea of a patterncompressor came from BLADE/Newcore,  who did  such  a 
thing for own purposes and released it together with the Octalyser.
I heard of it and began to code my own:
The  first  patternpacker  was written for DYNABUSTERS+ to  save  the  rare 
memory.  It was a simple run-lenght packer and so the compressionrates were 
quite bad (around 80% of the orginal patternsize).
But then I had another idea, which allows a packrate of around 30%.
Well,  this packer then was the used patternpacker for DYNABUSTERS+. As Scy 
registered for Octalyser,  I finally had the possibility to compare  Blades 
packer with mine.
Dissapointing for me: Blades one was better...

So I thought about another method, or how to improve my algorithms.
Well,  I created a sequencelist,  that saves any doubles -> And that really 
helped a lot!!
So here is PMD3! And it beats Blades packer is all cases I compared them!!!




III. The Format
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 File-Description for
  Module-Patterncompressor v3.0

  Offsets  |Lenght   | Meaning
 ----------+---------+--------------------------------------------------
         0 | 1080    |= Orginal ProTracker-Header
 ----------+---------+--------------------------------------------------
      1080 | 4       | ID: 'PMD3' - 4 Channels
           |         |     'PMd3' - 8 Channels
           |         |     'pMD3' - 4 Channels / Delta-Samples 
           |         |     'pMd3' - 8 Channels / Delta-Samples 
 ----------+---------+--------------------------------------------------
      1084 | 4       | Control-Len
      1088 | 4       | Data-Len
 ----------+---------+--------------------------------------------------
      1092 |p*trcks*8| For every pattern:
           |         |    For all tracks:  Control-Offs .l   (C-Offs)
           |         |                        Data-Offs .l   (D-Offs)
 ----------+---------+--------------------------------------------------
 How you can find the other needed addresses:
  1092+p*tracks*8                         --> Control-Bytes  (C-Adr)
  1092+p*tracks*8+Control-Len             --> Data-Longs     (D-Adr)
  1092+p*tracks*8+Control-Len+Data-Len    --> Samples
 ----------+---------+--------------------------------------------------
 (C-Adr)+(C-Offs) --> Address of the Control-Bytes-Start for Track
 (D-Adr)+(D-Offs) --> Address of the Data-Longs-Start for Track
 ----------+---------+--------------------------------------------------
 How the data is encoded:
 The Controlbytes are coded that way:
       76543210
       ||||||++--- Runlenght
       ++++++----- Data-Offset
 Mask out the upper six Bits and you get how often you have to repeat the
 Data-Long (like for DBRA, that means: 0=One time, 3=Four times!)
 To get the Data-Long just mask out the lower two Bits and add that value to
 the Data-Long-Startadr of the Track you want to depack.
 Track is finished when 64 Longs are depacked.

A  depacked  pattern is absolutely identical to a normal  pattern,  so  you 
don't  have to rewrite your player completely if you really want to use  my 
compressed format.



IV. The Sampleprepacker (PMD3_SPP.PRG)
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Well,  this prepacker just creates Deltasamples using a logharitmic  table, 
so that the sample will sound a bit different.
You  can  enter  how many different delta-values will  be  used  to  create 
deltasamples.
The  deltas  are  stored as bytes.  That's why it becomes just  a  kind  of 
prepacker,  'coz  the size of a PMD3-Module doesn't get smaller  by  simply 
using the PMD3_SPP.PRG
Just if you use a 'REAL' packer afterwards you can see how the samples  can 
be packed better than without it.

Here's  a little algorithm to show how the deltasample can be converted  to 
eight bit samples again:
                    moveq #0,D0
delta_to_8bit:      add.b (a0),d0       ;a0 points to samplestart
                    move.b d0,(a0)+
                    subq.l #1,d1        ;d1 is the samplelenght
                    bgt.s  delta_to_8bit      

V. Address
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  DYNACORE
  ANDREAS JOHN
  SCHULZENSTR.36
  76771 H™RDT
  GERMANY
    
MAUSNET:                 Andreas John@KA
E-MAIL:          [email protected]


CALL .tSCc. WHQ: NIGHTBOX:  +49 (0) 8974995006 (mail to TSCC)

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