From 086b25d40a8fc3606d70c32af7f6af178e2d804d Mon Sep 17 00:00:00 2001 From: Christian Schaller Date: Fri, 6 May 2005 11:41:28 +0000 Subject: remove gst-libs from gst-plugins module as it is in gst-plugins-base now Original commit message from CVS: remove gst-libs from gst-plugins module as it is in gst-plugins-base now --- gst-libs/gst/resample/README | 62 -------------------------------------------- 1 file changed, 62 deletions(-) delete mode 100644 gst-libs/gst/resample/README (limited to 'gst-libs/gst/resample/README') diff --git a/gst-libs/gst/resample/README b/gst-libs/gst/resample/README deleted file mode 100644 index f7db1105..00000000 --- a/gst-libs/gst/resample/README +++ /dev/null @@ -1,62 +0,0 @@ - -This is a snapshot of my current work developing an audio -resampling library. While working on this library, I started -writing lots of general purpose functions that should really -be part of a larger library. Rather than have a constantly -changing library, and since the current code is capable, I -decided to freeze this codebase for use with gstreamer, and -move active development of the code elsewhere. - -The algorithm used is based on Shannon's theorem, which says -that you can recreate an input signal from equidistant samples -using a sin(x)/x filter; thus, you can create new samples from -the regenerated input signal. Since sin(x)/x is expensive to -evaluate, an interpolated lookup table is used. Also, a -windowing function (1-x^2)^2 is used, which aids the convergence -of sin(x)/x for lower frequencies at the expense of higher. - -There is one tunable parameter, which is the filter length. -Longer filter lengths are obviously slower, but more accurate. -There's not much reason to use a filter length longer than 64, -since other approximations start to dominate. Filter lengths -as short as 8 are audially acceptable, but should not be -considered for serious work. - -Performance: A PowerPC G4 at 400 Mhz can resample 2 audio -channels at almost 10x speed with a filter length of 64, without -using Altivec extensions. (My goal was 10x speed, which I almost -reached. Maybe later.) - -Limitations: Currently only supports streams in the form of -interleaved signed 16-bit samples. - -The test.c program is a simple regression test. It creates a -test input pattern (1 sec at 48 khz) that is a frequency ramp -from 0 to 24000 hz, and then converts it to 44100 hz using a -filter length of 64. It then compares the result to the same -pattern generated at 44100 hz, and outputs the result to the -file "out". - -A graph of the correct output should have field 2 and field 4 -almost equal (plus/minus 1) up to about sample 40000 (which -corresponds to 20 khz), and then field 2 should be close to 0 -above that. Running the test program will print to stdout -something like the following: - - time 0.112526 - average error 10k=0.4105 22k=639.34 - -The average error is RMS error over the range [0-10khz] and -[0-22khz], and is expressed in sample values, for an input -amplitude of 16000. Note that RMS errors below 1.0 can't -really be compared, but basically this shows that below -10 khz, the resampler is nearly perfect. Most of the error -is concentrated above 20 khz. - -If the average error is significantly larger after modifying -the code, it's probably not good. - - - -dave... - -- cgit v1.2.1