bobp@amiga.UUCP (Robert S. Pariseau) (11/08/85)
I've received some mail asking for this stuff, so here's a copy of a
posting I made to BIX recently:
=================================
TITLE: Sampled Sound Data Files
This note (ahem) describes the format of the sampled sound data files
found on the instruments disk which is used with the Music demo on
the dealer's Workbench Demo Disk. This stuff is lifted from the musty
files of Sam-the-audio-expert. If you don't understand some of the
terminology used, you're out of luck until Sam-tae returns from
vacation. I've looked at the source for the Music demo and, like
all our demo code (see comment elsewhere in this conference), it's
full of bees and spiders! That's why we don't give it out. In any
event, I'll do my best to guide you. Hold on tightly now....
Each sampled sound begins with the CompressedSample header described
below. Each sound is comprised of one or more octaves. Each octave
is comprised of one or more segments. A segment contains 2**N cycles
of the waveform in tune, usually bounded by zero crossings. The
sampled sound may designate the ending segments as looping segments.
The looping and unlooping segments are not to be confused with
an envelope or ADSR. An ADSR envelope is independent and controlled with
variables in the Note structure. These segments will be played
repeatedly during the Sustain and Release of the note.
Each octave's segment size is twice as large as the octave above it.
Example:
highOctSize = 4;
lowOctSize = 7;
numSegments = 5;
loopStart = 3;
If each digit below represents 16 bytes of data, then each segment
would take the space indicated by the number of digits with the segment
number. Segments 3 & 4 of an octave would be repeated for looping.
____
/ \ loop
V |
012340011223344000011112222333344440000000011111111222222223333333344444444
\ /\__ __/\___________________/\_______________ _______________/
\ / \ / \ /
highest next lowest
octave octave octave
<--low memory . . . high memory-->
The notes for a given octave are produced by playing the sample for that
octave at a sampling rate of between 14 and 28KHz (one octave). The
Music demo uses a trivial Vertical Blank Interrupt Server to signal
it regularly once per video frame. These "ticks" are used to advance
through the ADSR envelope described in the Note structure. Envelope
generation is done by issuing the appropriate audio device command to
change audio channel volume.
The actual period values used to produce the scale are
240, 226, 214, 202, 190, 180, 170, 160, 151, 143, 135, 127.
The meanings of Very Slow to Very Fast attack, decay, and release are
built into the Music demo -- as are the default settings of these for
each instrument. Sustain is determined by how long the player keeps
the key depressed.
For more info on all of this, refer to the Amiga Hardware Manual and
the Amiga ROM Kernel Manual.
--------------------------Sampled sound header file
/* The looping octaves technique number */
#define TL_LOOPING_OCTAVES 1
#define MAX_SAMPLE_SIZE (sizeof(struct CompressedSample)+2*128*128)
/* compressed sampled sound data structure */
/* THIS IS THE HEADER ON A SAMPLED SOUND DATA FILE */
struct CompressedSample {
UWORD technique; /* technique number */
UWORD numSegments; /* number of segments in sample (same for all octaves)*/
UWORD loopStart; /* first segment of loop (= numSegments for no loop) */
UBYTE highOctSize; /* highest octave segment size (power of 2) */
UBYTE lowOctSize; /* lowest octave segment size (power of 2) */
BYTE samples[1]; /* start of samples */
};
/* note descriptor */
/* THIS STRUCTURE IS USED TO KEEP ADSR INFO WITH A SOUND IN MEMORY */
struct Note {
struct CompressedSample *sample; /* sound sample in compressed format */
UWORD attack; /* attack time in msec. (0 - 65535) */
UWORD decay; /* decay time in msec., 0 for sustain (1 - 65535) */
UWORD release; /* release time in msec. (0 - 65535) */
UBYTE channel; /* audio channel number (0 - 3) */
UBYTE pitch; /* note number, 0 for A (0 - highest octave of sound) */
UBYTE level; /* sustain level in 0.1875 db steps (0 - 255) */
UBYTE vibDepth; /* vibrato depth, up to one whole step (0 - 255) */
UBYTE vibRate; /* vibrato rate, (0 - 255) */
};