SK(1)               UNIX Programmer's Manual                SK(1)



NAME
     st - Sound Tools - sound sample file and effects libraries.

SYNOPSIS
     cc _f_i_l_e._c -o _f_i_l_e libsk.a

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

     Sound Tools includes skeleton C files to assist you in writ-
     ing 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 readers 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 exam-
     ple:
          *obuf++ = (*ibuf++ * *ibuf++)/2;
     would _n_o_t mix down left and right channels into one mono-
     phonic 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.  Quadraphonic data is stored in this
     order: left front, right front, left rear, right rear.

FORMATS
     A _f_o_r_m_a_t 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 _f_o_r_m_a_t
     operates from two data structures: a format structure, and a
     private structure.





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SK(1)               UNIX Programmer's Manual                SK(1)



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

     The _p_r_i_v_a_t_e area is just a preallocated data array for the
     _f_o_r_m_a_t 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 _f_o_r_m_a_t 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 sam-
                         ples 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 appropri-
                         ate 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 argu-
                         ment list for the effect.



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SK(1)               UNIX Programmer's Manual                SK(1)



     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 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 fill the output
                         buffer.

     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.  _s_t_o_p 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 mul-
     tiplies 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 "obviously 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.





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SK(1)               UNIX Programmer's Manual                SK(1)



     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.

     The human ear can't really hear better than 20 bits.  With
     an internal format of 16 bits, we will eventually destroy
     information when used to mix CD's.  The internal format
     should be 24-bit signed data.  But, with 24 bits you still
     have to be careful multiplying.  Check the ``vibro'' effect
     for how it handles this problem.












































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