A couple of years ago I tried some experiments with resampling in which I downsampled a 24/96 file to 16/44.1, then upsampled again back to 24/96. I used the freeware Audio DiffMaker to take the difference between the "round trip" resampled file and the original. DiffMaker determines the optimum scale factor and delay to apply to the "test" file to get the best null between it and the "reference" file.
When doing this with r8brain, I found clicks in the difference file, even at the highest quality setting. This caused me to look around for another resampler. I finally found the command-line utility SoX. The first thing that happened when I tried it on the same input file was that it gave me a warning about clipped samples in the downsampled file. SoX has the option of scaling, and I did this so that clipped samples were eliminated in both the downsampled file and the "round trip" downsampled->upsampled one. Then when I found the difference using DiffMaker, the clicks were gone! This caused me to abandon r8brain. The only thing I could hear in the difference file was a slight amount of hiss, and in order to hear that I had to turn up my system all the way and put my ear right up against the speaker. Great care should be used when doing this, as DiffMaker has a bug that causes an audible blip in the difference file at the beginning, even when subtracting two identical files. The command line I used with SoX was like the one below: sox -v 0.983 track-01-01[0]-01-[L-R]-24-96000.wav -b 16 "01 - Box Of Rain.wav" rate -v 44100 dither The first -v specifies that what follows is a volume adjustment. I've scaled the data by 0.983, which was just barely enough to prevent the clipping warning message. The next argument is the input file name. Following the file name is "-b 16", which says the output file should be 16 bits. Next is the output file name. "rate -v" says to do sample rate conversion with the -v option, which is the highest quality conversion available with SoX. Following this is the sample rate of the output file in Hz. The "dither" option specifies that dither with a triangular PDF will be used. SoX is amazingly powerful, and the sample rate conversion above just scratches the surface of what it can do. I'm quite confident that when a good resampler is used with the appropriate scale factor needed to eliminate clipped samples, that resampling down to 16/44.1 will be transparent in all but the most extreme of cases. I haven't tried it with really crazy types of files like Tom Danley's fireworks recordings though. -- andy_c ------------------------------------------------------------------------ andy_c's Profile: http://forums.slimdevices.com/member.php?userid=3128 View this thread: http://forums.slimdevices.com/showthread.php?t=93990 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
