AVR
From Just Solve the File Format Problem
AVR Audio Visual Research sample file format. Public domain.
The .AVR sample file format sees use on the Atari ST(e) and older Apple Macintosh computers. Commonly used for 8 bit audio, sometimes 16.
Some Atari music software supporting AVR: Quartet, Zero-X, Breakthru, EPSS, Sound Lab.
/* All fields are big endian. */
struct AVR_HEADER {
char magic_number[4]; /* "2BIT" */
char title[8]; /* Title, padded with 0s. No 0 terminator is
needed at the end, all 8 characters can
be used for text. */
signed short int stereo; /* -1 = stereo, 0 = mono. Stereo data is
interleaved like a .wav file, LRLRLR.. */
signed short int bits; /* Bits per sample. Usually 8 or 16. 16 bit
sample data is big endian. */
signed short int signed; /* -1 = signed, 0 = unsigned. The convention
is to use unsigned for 8 bit recordings.
Some programs may rely on this. */
signed short int loop; /* -1 = loop enabled, 0 = loop disabled. */
signed short int midi_note; /* Can be one of these three:
-1: No MIDI note assigned (most common).
0xffnn: MIDI note number nn assigned.
0xllhh: MIDI note ll for the low key,
and MIDI note hh for the high
key. This mode isn't well-
documented, presumably it
specifies a range of keys to map
the sample across. In this case
it is unclear how the root note
is determined. */
unsigned long int samp_rate; /* Sample rate in Hz. IMPORTANT: the upper
byte of this must be masked off.
The upper byte contains undocumented data
unrelated to sample rate, very frequently
non-zero.
samp_rate = samp_rate & 0x00ffffff;
Some programs will only look at the low
two bytes of this field, limiting the
maximum sample rate to 65535 Hz. */
unsigned long int length; /* Recording length in sample periods. */
unsigned long int loop_start; /* Loop start point in sample periods.
If the loop is switched off, this can be
set to 0 (but doesn't have to be).
This should be <= loop_end, but don't
rely on this when reading a file. */
unsigned long int loop_end; /* Loop end point in sample periods. This
points to the first sample which is never
played (the previous sample is the last
one played before looping back to
loop_start). If there is no data to the
right of the loop_end point, this will
have the same value as length.
If the loop is switched off, this can be
set to 0 (but doesn't have to be).
This should be <= length, but don't rely
on this when reading a file. */
signed short int key_split; /* Undocumented, usually 0. */
signed short int compression; /* Undocumented, usually 0. */
signed short int reserved; /* Undocumented, usually 0. */
char title_extra[20] /* Usually 0. Some programs use this space
as additional characters for title[],
only when title[7] is non-zero.
When writing a file, it is best to set
these to zero.
Some programs may use this for other
purposes. */
char comment[64]; /* Text comment. Padded with 0s.
It is unclear whether this needs to be
terminated with a 0. Assume un-terminated
when reading, and write terminated. */
}; /* Total length of header: 128 bytes fixed-size. Sample data begins
immediately after header. */
Definitions:
signed short int: 16 bits big-endian two's complement, -32768 to +32767.
unsigned long int: 32 bits big-endian, 0 to +4294967296.
char: A single byte.
0: A zero value or byte (not an ASCII '0').
0xnn A hexadecimal value nn.
Sample: One or two bytes making up a single numerical value for
one data point on one channel.
Sample period: A group of samples, one sample for each channel.
Recording: The whole sample data. The entire file, sans header.
Signed: Sample data represented by signed two's complement
integers.
Unsigned: Sample data represented by unsigned integers, no-signal
idle level (0 volts) stored as 128 (8 bit) or
32768 (16 bit). Values above this represent positive
voltages. To convert from signed to unsigned or vice-
versa, invert the most significant bit.
