Re: Fwd: Re: [Jsynthlib-devel] Method to pack/unpack 7-bit bytes to/from 8-bit bytes?

[Joe E. <jo...@em...>]

Jeff Weber wrote:

>--- Joe Emenaker <jo...@em...> wrote:
>  
>
>>I can only think of *two*
>>different ways of doing the 
>>conversion that aren't completely insane...
>>    
>>
>For each group of seven bytes the FCB1010 takes bit 8
>from each byte and creates and 8th byte at the end of
>the group. The representation of the 8th byte is:
>0, msb byte 6, msb byte 5, msb byte 4...msb byte 0
>
>Make sense?
>  
>
Doh! That's one of the "insane" ways. :) After thinking about it, it's 
probably not all that insane. In fact, the code to to the 
encoding/decoding is probably tighter than the code to do it the Alesis way.

The Alesis way is a little easier to draw on paper. Just take the 
meaningful 7 bits of the eight MIDI bytes and string them together. You 
now have 56 bits. Take the first 8 and that's your first "real" byte, 
the next 8 are your next byte, etc.

So, MIDI bytes like 0x37 0x21 0x44 ... would give you a string of bits like:
  0110111 0100001 1000100 ...

re-grouped as 8-bit sets, you get:
 01101110 10000110 00100...
or...
 0x6E 0x86 ...

Anyhow, I'm still not convinced that each synthdriver author should have 
to re-write nibbilizers each time. I'm sure that there are a fixed 
number of ways were going to see this done in real life... and they're 
all going to need to be accessible to the XML driver *anyway*... so I 
still vote for consolidating them somewhere.

- Joe