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ST(3)											    ST(3)

NAME
       libst - Sound Tools : sound sample file and effects libraries.

SYNOPSIS
       cc file.c -o file libst.a

DESCRIPTION
       Sound Tools  is	a  library  of sound sample file format readers/writers and sound effects
       processors.

       Sound Tools includes skeleton C files to assist you in writing new  formats  and  effects.
       The  full skeleton driver, skel.c, helps you write drivers for a new format which has data
       structures.  The simple skeleton drivers help you write a new driver for raw  (headerless)
       formats, or for formats which just have a simple header followed by raw data.

       Most  sound sample formats are fairly simple: they are just a string of bytes or words and
       are presumed to be sampled at a known data rate.  Most of them have a short data structure
       at the beginning of the file.

INTERNALS
       The  Sound Tools formats and effects operate on an internal buffer format of signed 32-bit
       longs.  The data processing routines are called with buffers of these samples, and  buffer
       sizes which refer to the number of samples processed, not the number of bytes.  File read-
       ers translate the input samples to signed longs and return the number of longs read.   For
       example, data in linear signed byte format is left-shifted 24 bits.

       This does cause problems in processing the data.  For example:
	    *obuf++ = (*ibuf++ + *ibuf++)/2;
       would  not  mix	down  left  and  right	channels into one monophonic channel, because the
       resulting samples would overflow 32 bits.  Instead, the ``avg'' effects must use:
	    *obuf++ = *ibuf++/2 + *ibuf++/2;

       Stereo data is stored with the left and right speaker data in successive samples.  Quadra-
       phonic data is stored in this order: left front, right front, left rear, right rear.

FORMATS
       A format is responsible for translating between sound sample files and an internal buffer.
       The internal buffer is store in signed longs with a fixed sampling rate.  The format oper-
       ates from two data structures: a format structure, and a private structure.

       The  format structure contains a list of control parameters for the sample: sampling rate,
       data size (bytes, words, floats, etc.), encoding (unsigned, signed,  logarithmic),  number
       of  sound  channels.   It  also	contains other state information: whether the sample file
       needs to be byte-swapped, whether fseek() will work, its suffix, its file stream  pointer,
       its format pointer, and the private structure for the format .

       The  private  area  is  just  a	preallocated  data array for the format to use however it
       wishes.	It should have a defined data structure and cast the  array  to  that  structure.
       See voc.c for the use of a private data area.  Voc.c has to track the number of samples it
       writes and when finishing, seek back to the beginning of the file and write it  out.   The
       private	area  is  not very large.  The ``echo'' effect has to malloc() a much larger area
       for its delay line buffers.

       A format has 6 routines:

       startread	   Set up the format parameters, or read in a data  header,  or  do  what
			   needs to be done.

       read		   Given  a  buffer and a length: read up to that many samples, transform
			   them into signed long integers, and copy them into the buffer.  Return
			   the number of samples actually read.

       stopread 	   Do what needs to be done.

       startwrite	   Set	up  the format parameters, or write out a data header, or do what
			   needs to be done.

       write		   Given a buffer and a length: copy that many samples out of the buffer,
			   convert them from signed longs to the appropriate data, and write them
			   to the file.  If it can't write out all the samples, fail.

       stopwrite	   Fix up any file header, or do what needs to be done.

EFFECTS
       An effects loop has one input and one output stream.  It has 5 routines.

       getopts		   is called with a character string argument list for the effect.

       start		   is called with the signal parameters for the input and output streams.

       flow		   is called with input and output data buffers, and (by  reference)  the
			   input  and  output  data  buffer sizes.  It processes the input buffer
			   into the output buffer, and sets the size variables to the numbers  of
			   samples  actually  processed.   It is under no obligation to read from
			   the input buffer or write to the output buffer during the  same  call.
			   If  the  call returns ST_EOF then this should be used as an indication
			   that this effect will no longer read any  data  and	can  be  used  to
			   switch to drain mode sooner.

       drain		   is  called  after there are no more input data samples.  If the effect
			   wishes to generate more data samples it copies the generated data into
			   a  given  buffer  and  returns the number of samples generated.  If it
			   fills the buffer, it will be called again, etc.  The echo effect  uses
			   this to fade away.

       stop		   is  called  when there are no more input samples to process.  stop may
			   generate output samples on its own.	See echo.c for how  to	do  this,
			   and see that what it does is absolutely bogus.

COMMENTS
       Theoretically, formats can be used to manipulate several files inside one program.  Multi-
       sample files, for example the download for a sampling keyboard,	can  be  handled  cleanly
       with this feature.

PORTABILITY PROBLEMS
       Many  computers	don't supply arithmetic shifting, so do multiplies and divides instead of
       << and >>.  The compiler will do the right thing if the CPU supplies arithmetic shifting.

       Do all arithmetic conversions one stage at a time.  I've had too many problems with "obvi-
       ously clean" combinations.

       In  general,  don't  worry about "efficiency".  The sox.c base translator is disk-bound on
       any machine (other than a 8088 PC with an SMD disk controller).	Just  comment  your  code
       and  make  sure	it's clean and simple.	You'll find that DSP code is extremely painful to
       write as it is.

BUGS
       The HCOM format is not re-entrant; it can only be used once in a program.

       The program/library interface is pretty weak.  There's too much ad-hoc information which a
       program	is  supposed  to  gather up.  Sound Tools wants to be an object-oriented dataflow
       architecture.

					 October 15 1996				    ST(3)
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