155 lines
5 KiB
Plaintext
155 lines
5 KiB
Plaintext
README file for resample-1.x.tgz from the
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Digital Audio Resampling Home Page located at
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http://ccrma.stanford.edu/~jos/resample/.
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SOFTWARE FOR SAMPLING-RATE CONVERSION AND FIR DIGITAL FILTER DESIGN
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For installation instructions, read the INSTALL file in this directory.
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The resample program "resamples" a soundfile to change its sampling
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rate. For example, it can be used to convert the sampling rate from
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48 kHz (used by DAT machines) to 44.1 kHz (the standard sampling rate
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for Compact Discs). The command line for this operation would look
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something like
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resample -by 0.91875 dat.snd cd.snd
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or, more simply,
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resample -to 44100 dat.snd cd.snd
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Any reasonable sampling rate can be converted to any other.
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The windowfilter program designs Finite-Impulse-Response (FIR) digital
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filters by the so-called "window method." In this method, the ideal
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impulse response (a sinc function) is "windowed" by a Kaiser window (a
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popular window used in spectrum analysis).
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The resample program uses 32-bit fixed-point arithmetic: 16-bits data
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and 16-bits coefficients. The input soundfile must be 16-bit mono or
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stereo (interleaved) audio data.
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SNDLIB
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The program uses elements of Bill Schottstaedt's sndlib sound file
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library. This means resample can read many different kinds of sound
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file header (AIFF, WAV, NeXT, IRCAM, etc.).
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The sndlib files used by resample are included in this directory to
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ensure stability. The latest version of sndlib should be available as
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ftp://ccrma-ftp.stanford.edu/pub/Lisp/sndlib.tar.gz
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See sndlib.html in the sndlib distribution for documentation of SNDLIB.
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CONTENTS of ./src directory
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resample.c Sampling-rate conversion program.
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resample.1 Manual page for resample. Try "nroff -man resample.1".
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resamplesubs.c Subroutines used by resample.
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resample.h Configuration constants for the sampling rate converter.
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stdefs.h Machine-dependent definitions, useful constants and macros.
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windowfilter.c Program for designing FIR digital filters used by resample.
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windowfilter.1 Manual page for windowfilter.
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filterkit.c Library for filter design, application, and file management.
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filterkit.h Declarations (procedure prototypes) for the filterkit library.
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README This file.
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README.deemph A word about deemphasis filtering.
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LGPL GNU Lesser General Public License (LGPL)
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SNDLIB files:
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io.c
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audio.c
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headers.c
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sound.c
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sndlib.h
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sndlib-strings.h
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COPYING
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SNDLIB files are Copyright 2000 by Bill Schottstaedt <bil@ccrma.stanford.edu>.
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The remaining files in this package, unless otherwise noted, are
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Copyright 1994-2006 by Julius O. Smith III <jos@ccrma.stanford.edu>,
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all rights reserved. Permission to use and copy is granted subject to
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the terms of the "GNU Lesser General Public License" (LGPL) as
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published by the Free Software Foundation; either version 2.1 of the
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License, or any later version. In addition, we request that a copy of
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any modified files be sent by email to jos@ccrma.stanford.edu so that
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we may incorporate them into the CCRMA version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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FILTERKIT CONTENTS
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LpFilter() - Calculates the filter coeffs for a Kaiser-windowed
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low-pass filter with a given roll-off frequency. These
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coeffs are stored into a array of doubles.
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writeFilter() - Writes a filter to a file.
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makeFilter() - A section of the original SAIL program. Calls
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LpFilter() to create a filter, then scales the double
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coeffs into a array of half words.
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readFilter() - Reads a filter from a file.
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FilterUp() - Applies a filter to a given sample when up-converting.
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FilterUD() - Applies a filter to a given sample when up- or down-
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converting. Both are repoductions of the original SAIL
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program.
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initZerox() - Initialization routine for the zerox() function. Must
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be called before zerox() is called. This routine loads
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the correct filter so zerox() can use it.
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zerox() - Given a pointer into a sample, finds a zero-crossing on the
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interval [pointer-1:pointer+2] by iteration.
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Query() - Ask the user for a yes/no question with prompt, default,
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and optional help.
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GetUShort() - Ask the user for a unsigned short with prompt, default,
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and optional help.
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GetDouble() - Ask the user for a double with prompt, default, and
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optional help.
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GetString() - Ask the user for a string with prompt, default, and
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optional help.
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FILTER FILE FORMAT
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File Name: "F" Nmult "T" Nhc ".filter"
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example: "F13T8.filter" and "F27T8.filter"
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Structure of File:
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"ScaleFactor" LpScl
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"Length" Nwing
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"Coeffs:"
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Imp[0]
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Imp[1]
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Imp[Nwing-1]
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"Differences:"
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ImpD[0]
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ImpD[1]
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ImpD[Nwing-1]
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EOF
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where: Something enclosed in "" indicates specific characters in the file.
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Nmult, Nwing, Imp[], and ImpD[] are variables (HWORD)
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Npc is a conversion constant.
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EOF is the end of the file.
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See writeFilter() and readFilter() in "filterkit.c" for more details.
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