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RATECONV - a universal sample rate converter

This is a universal tool to convert sample rates of audio signals consisting of signed 16bit data, mono or stereo. It is designed as stream filter around an effcient internal structure. On-the-fly conversions while recording or playing sound are possible although they depend on CPU-speed and other specific demands. It can also be used as a low-pass filter without changing rates. Target platforms are un*x systems.

Its flexibility helps to overcome restrictions in quality, usable bandwith or rate-ratios inherent to other solutions. It is easy to outperform the quality of simple rate conversion schemes, e.g. the one which comes with the well known sound format conversion package `sox' by Lance Norskog (But `sox' seems great for all other types of format conversion).

Although standard solutions are provided be warned that there is no quick solution to meet all objectives at the same time with computational efficiency. This is because one has to trade between quality, usable bandwith and efficiency. The term `universal' implies that the trade is left up to you to decide. The provided documentation allows development of adapted solutions to the problem of rate conversion in audio or, more generally speaking, resampling of a given bandlimited function.

Contents

Usage
Installation
Copyright and disclaimer
Author

1. Usage

        This is at a glance what you get once you've compiled and invoked
        `rateconv':

        Sample rate conversion from stdin to stdout  [...]
        Usage: rateconv [-hlms] <fsin> <fgK> <fgG> <lenght> <up> <down> [..
          -h -l     sample format HB,LB or LB,HB (default)
          -m -s     mono (default) or stereo mode
          <fsin>    input sampling frequency in Hz
          <fgK>     sinc-filter cutoff frequency
          <fgG>     gaussian-window key frequency (6.8dB-down point)
          <length>  lenght of IR of resulting FIR-filter (1...1024)
          <up>      upsampling factor (1...1024)
          <down>    downsampling factor
          <gain>    over-all-gain (default 0.8 safe on filter overshoot)

        Now the task in general would be to find suitable paramters for
        the specific demands you have. The shell scripts in the `examples'
        directory use some predefined parameters and call rateconv
        directly. Their computational efficiency versus quality varies
        (see the internal comments). If you don't mind some inefficiency,
        the shell script `rcv' should satisfy almost all your demands,
        showing this upon invocation:

        High quality rate conversion stdin to stdout  [...]
        Usage:   rcv [-hlms] <up> <down> [<gain>]
        Options: -hlms see external command rateconv
        Args:    <up>,<down> are positive integer values
                 their ratio determines the rate change
                 which must be greater than about 0.16
                 <up> may not exceed a value of 1024
                 small rate changes compute more efficiently
                 <gain> default is 0.8 to avoid overload
        Specs:   1dB-edge-frequency is at 9/20 of the smaller rate
                 S/N and mirror frequency suppression is >= 96dB

        If you want to tailor the paramters of RATECONV to meet your
        specific needs please read the file `rateconv.txt'.

2. Installation

        RATECONV was developed on SYSV386R3.2 (Intel-Architecture).
        With the appropriate flags set in Makefile it should work on
        a lot of other systems and architectures too. It definitely
        runs on Linux/386, SunOS4.1.3/sparc, HP-UX8.0/9000-370 and
        IRIX5.3/mips. 

        Edit Makefile and `make', install rateconv manually to .../bin
        together with rcv and the examples you desire.

3. Copyright and disclaimer

        Redistribution and use of this software, modifcation and inclusion
        into other forms of software are permitted provided that the
        following conditions are met:

        1. Redistributions of this software must retain the above copyright
           notice, this list of conditions and the following disclaimer.
        2. If this software is redistributed in a modified condition
           it must reveal clearly that it has been modified.
        
        THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
        AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
        TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
        PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR
        CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
        EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
        PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
        PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
        OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
        (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
        USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
        DAMAGE.

4. Author

Questions, remarks, suggestions and advice are welcome

                        Markus Mummert
        * SNAILMAIL:    Emanuelstr. 27
                        D-80796 Munich
                        Germany
        * PHONE:        +49 89 300 44 70
        * MAIL:         <mum@mmk.e-technik.tu-muenchen.de>
                        Please Note: this adress is checked depending
                        on traffic - maybe only twice a month at the worst.
                        My own system is offline.

===EOT===$Id: README,v 1.5 1995/12/09 02:16:21 mummert Exp mummert $