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author | Max Horn | 2003-07-24 17:46:38 +0000 |
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committer | Max Horn | 2003-07-24 17:46:38 +0000 |
commit | b9d380bba43b25e1654b320a42b05499c060656c (patch) | |
tree | a882712c93b94c0e984c801f1a6ff8bcee515a40 /sound/resample.h | |
parent | becd70d243d456af9595ae0cc37e72b1489736c5 (diff) | |
download | scummvm-rg350-b9d380bba43b25e1654b320a42b05499c060656c.tar.gz scummvm-rg350-b9d380bba43b25e1654b320a42b05499c060656c.tar.bz2 scummvm-rg350-b9d380bba43b25e1654b320a42b05499c060656c.zip |
new files, based on SoX (http://sox.sf.net): better resampling code. Note that my mixer.cpp changes are on purpose not yet in CVS since they are not complete. Only reasons I checkin these files is that it's much more comfortable to have CVS, since I need to rewrite parts of resample.cpp now (I already have lots of modifications in). Also expect more OO in the future
svn-id: r9176
Diffstat (limited to 'sound/resample.h')
-rw-r--r-- | sound/resample.h | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/sound/resample.h b/sound/resample.h new file mode 100644 index 0000000000..f66ad75a5d --- /dev/null +++ b/sound/resample.h @@ -0,0 +1,61 @@ +/* + * FILE: resample.h + * BY: Julius Smith (at CCRMA, Stanford U) + * C BY: translated from SAIL to C by Christopher Lee Fraley + * (cf0v@andrew.cmu.edu) + * DATE: 7-JUN-88 + * VERS: 2.0 (17-JUN-88, 3:00pm) + */ + +/* + * October 29, 1999 + * Various changes, bugfixes(?), increased precision, by Stan Brooks. + * + * This source code is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + * + */ + +/* Conversion constants */ +#define Lc 7 +#define Nc (1<<Lc) +#define La 16 +#define Na (1<<La) +#define Lp (Lc+La) +#define Np (1<<Lp) +#define Amask (Na-1) +#define Pmask (Np-1) + +#define MAXNWING (80<<Lc) +/* Description of constants: + * + * Nc - is the number of look-up values available for the lowpass filter + * between the beginning of its impulse response and the "cutoff time" + * of the filter. The cutoff time is defined as the reciprocal of the + * lowpass-filter cut off frequence in Hz. For example, if the + * lowpass filter were a sinc function, Nc would be the index of the + * impulse-response lookup-table corresponding to the first zero- + * crossing of the sinc function. (The inverse first zero-crossing + * time of a sinc function equals its nominal cutoff frequency in Hz.) + * Nc must be a power of 2 due to the details of the current + * implementation. The default value of 128 is sufficiently high that + * using linear interpolation to fill in between the table entries + * gives approximately 16-bit precision, and quadratic interpolation + * gives about 23-bit (float) precision in filter coefficients. + * + * Lc - is log base 2 of Nc. + * + * La - is the number of bits devoted to linear interpolation of the + * filter coefficients. + * + * Lp - is La + Lc, the number of bits to the right of the binary point + * in the integer "time" variable. To the left of the point, it indexes + * the input array (X), and to the right, it is interpreted as a number + * between 0 and 1 sample of the input X. The default value of 23 is + * about right. There is a constraint that the filter window must be + * "addressable" in a int32_t, more precisely, if Nmult is the number + * of sinc zero-crossings in the right wing of the filter window, then + * (Nwing<<Lp) must be expressible in 31 bits. + * + */ |