signed 8 bit to "sign and magnitude" handler needed [PART ONE]

[stephen barncard]

This isn't that long a message but it appears I've pushed the limit.
THis is part one.

Hi gang,
Continuing on the "exporting aiff files from audioclips" quest, I discovered
that 'some' (about 10%) of the exported files data would not play correctly.
They sounded distorted and loud at full scale. Digging in further, I
discovered that 8 bit AIFF files are not signed (due to their history), but
instead are ( I think ) "sign and magnitude" 8 bit.

So I need to convert the data for just the 8 bit files.

I know this is dumb ass simple, but I've been staring at these numbers for
too ling and need some fresh eyes. I am *seeking a handler in Livecode* to
convert numbers between 0-255 (what I think is) two's compliment 8 bit to
(what I think is) "sign and magnitude" numbers between 0-255.

that is, I need to convert a number series that looks like below
(word wrap is inevitable.)

00000000 80 7F 7F 7F 7E 7E 7E 7D 7D 7C 7C 7B 7B 7B 7A 7A

00000010 79 79 78 78 78 78 78 77 77 77 77 77 77 77 77 77

00000020 77 78 78 78 78 79 7A 7A 7B 7B 7C 7D 7D 7E 7F 80

00000030 81 81 83 83 84 85 86 87 88 89 8A 8B 8C 8C 8C 8E

00000040 8E 8F 90 90 90 91 91 91 92 91 91 91 92 91 91 90

00000050 90 90 8E 8E 8D 8C 8B 8A 89 88 87 85 84 83 81 80

00000060 7F 7D 7B 7A 79 77 76 75 73 72 71 6F 6F 6D 6C 6B


(this is the same sine wave going above and below center in both lists)



to be converted to numbers that look like this:


00000000 00 FF FF FF FE FE FE FD FD FC FC FB FB FB FA FA

00000010 F9 F9 F8 F8 F8 F8 F8 F7 F7 F7 F7 F7 F7 F7 F7 F7

00000020 F7 F8 F8 F8 F8 F9 FA FA FB FB FC FD FD FE FF 00

00000030 01 01 03 03 04 05 06 07 08 09 0A 0B 0C 0C 0C 0E

00000040 0E 0F 10 10 10 11 11 11 12 11 11 11 12 11 11 10

00000050 10 10 0E 0E 0D 0C 0B 0A 09 08 07 05 04 03 01 00

00000060 FF FD FB FA F9 F7 F6 F5 F3 F2 F1 EF EF ED EC EB


(this is a SSND chunk dump from an audio file that plays correctly.)

(part two will show the PHP code I tried to convert but failed)

-- 



Stephen Barncard
San Francisco Ca. USA

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