Vectronix 2/VECTRONIX2.iso/FILES_10/DEVELOP.LZH/AVR_FORM.TXT

Text File | 1992-10-19 | 6KB | 137 lines

                         A.V.R. PRO SERIES 16m

                             Appendix III

                         Sample Data Formats
                         -------------------

        Here is a brief description of the AVR Sample format

        The first 128 Byte on an AVR sound file on diac contain a sound file
header. The first BYTE or WORD immediately following the header is the first
BYTE or WORD of the sound sample itself. The contents of the header are as
follows


    OFFSET    SIZE      DESCRITPTION
              (BYTES)
  ---------   -------   ----------------------------------------------------

    0 -   3      4      4 BYTE ASCII CHARACTER I.D. CONTAINS '2BIT'

    4 -  11      8      8 BYTE ASCII CHARACTER SAMPLE NAME
                        UNUSED BYTES PADDED WITH NULL ($00).

   12 -  13      2      WORD = 0 FOR MONO $FFFF FOR STEREO SAMPLE

   14 -  15      2      WORD = SAMPLE RESOLUTION $0008 (8 BIT)
                        $0010 (16 BIT)

   16 -  17      2      WORD = $0000 UNSIGNED SAMPLE
                        WORD = $FFFF SIGNED SAMPLE

   18 -  19      2      WORD = $0000 NON-LOOPING SAMPLE
                        WORD = $FFFF LOOPING SAMPLE

   20 -  21      2      WORD = ASSIGNED MIDI NOTE / SPLIT
                        $FFFF = NO ASSIGNMENT (DEFAULT)
                        $FFxx = SINGLE KEY NOTE ASSIGNMENT
                        $LLHH = KEY SPLIT, TWO BYTES, NOTE LOW/NOTE HI

   22 -  25      4      LONG = SAMPLE SPEED SPLIT INTO 1 BYTE & 3 BYTES
                        BYTE 22      = 0 TO 7 OR $FF
                        BYTE 23 - 25 = 3 BYTE SAMPLE FREQUENCY IN HERTZ

   26 -  29      4      LONG LENGTH OF SAMPLE IN DATA BYTES OR WORDS

   30 -  33      4      LONG FIRST LOOP POINT (OFFSET IN DATA WORDS)
                        FORCE $0000 IF UNUSED

   34 -  37      4      LONG END LOOP POINT (OFFSET IN DATA WORDS)
                        FORCE TO SAMPLE LENGTH IF UNUSED

   38 -  39      2      - DO NOT USE - RESERVED AREA - MIDI KEYBOARD SPLIT

   40 -  41      2      - DO NOT USE - RESERVED AREA - SAMPLE COMPRESSION

   42 -  43      2      - DO NOT USE - RESERVED AREA - FILL WITH $00

   44 -  63     20      FILENAME EXTENSION. FILLED WITH $00 IF UNUSED

   64 - 127     64      FREE AREA FOR DEFINITION BY USER. MAY HAVE ASCII
                        MESSAGE OR OTHER USER DEFINED DATA

  128 - EOF             -SAMPLE- Held in format described by header.


                             Appendix - Page 13



This format represents a useful header which can be used to describe not
only 16 Bit samples, but has the flexibility built into it to cater for
MONO/STEREO and 8, 12, 14, and 16 BIT data sizes. 2-BIT SYSTEMS recommend,
that users DO NOT occupy the reserved space in the first 64 BYTES of the
header, the last 64 BYTES have been provided for micellanous use and abuse.

If the user is developing software which uses the AVR format, please note
the following :-

When reading samples
--------------------

        i) Always check for the first 4 BYTES of the sample file for '2BIT'
before attempting to load in any sample from disc. If this header is found,
then it can be assumed, that the smple is in AVR format, no matter what the
file extension is. It is useful, though not important, to save AVR files out
as XXXX.AVR.

        ii) After having established that the sample is indeed an AVR file,
load the 128 BYTE header into a seperate area of memory. Interpret this header
before attempting to load the rest of the file. This is important for a number
of reasons, the least of which is, that if a Stereo or 16 BIT sample were just
about to be loaded, the load address for the sampl block should be made on a
WORD boundary.

        iii) Do not take anything for grated about the sample. Ensure, that
all of the important parameters have been read and interpreted. E.G. SIGN
status. If your program can only use BYTE EXCESS samples then ensure that the
samples is not signed (and un-sign it if it is).

        iv) When reading the FREQUENCY long word, mask off the top 8 BITS.
These bits were used in ST REPLAY, PEPLAY PROFESSIONAL and the first version
of the PRO-SERIES editors. This byte took the form of a value from 0 to 7
which was used to denote a fixed SYSTEM frequency (0 = 5 kHz, 7 = 48 kHz
etc.). If this value is read as $FF, then the editor assumes that the
sample frequency is not immediately compatible with the choice which the
cartridge and EDITOR support.

When writing a file
-------------------

        i) ALWAYS wipe the eintrire header area with zero's when constructing
a new header.

        ii) ALWAYS force default values and never leave RUBBISH in areas
unused by the program in question, remember, another program may look for
DATA which is nonsense otherwise.

        iii) If looping is not used within an sample, ALWAYS force the start
loop to be zero and end loop to match the sample length.

        iv) When writing the sample record frequency long word into the
header, ensure that the default of $FF is placed into the top 8 BITS.

SIZES and POINTER OFFSETS
-------------------------

        Please note the use of the phrase 'WORD size' when expressing the
size of a sample or the offset of the loop pointers from the start of the
sample. It is assumed that if the sample is an 8 BIT sample (or less), then
the WORD size is BYTE. If the sample is greater that 8 BITS then the size is
assumed to be a 16 BIT data WORD. Hence a 16 BIT file size of 10000 words
would actually be 20000 BYTES in length. The value stored in the header
should be 10000.

                             Appendix - Page 14