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

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.
+ *
+ */