jkeny wrote: > Right, so your statement "No DAC playing back 176.4kHz should touch the > audible band " was meaningless to this test & only confuses matters. A > minimum phase filter > > Let's see what Archimago did then - *"I took ~1 minute of these three > 24/44 or 16/44 recordings and using SoX, upsampled them to 24/176.4 with > either the linear or minimum phase upsampling algorithm, re-naming one > file A and another B." * > > So he used an upsampling algorithm of either minimum or linear phase to > bring these files to 24/176. > > > > > > > > Correct. > > > > > > > > > > > > Now tell me how pre-ringing at the Nyquist frequency of 88KHz is of > > > interest to anyone & what this test is intended to do?> > > > > > > > That snide comment just shows the monumental amount of relevant > > technical information that you don't know about upsampling, jkeny. > > > > Upsampling is done by zero-filling the input file, followed by a > > brick wall low pass filter whose corner frequency is based on the > > sample rate of the original file. > > > > The filtering is required because the original file has been > > expanded into the output file by putting in samples whose value is > > equal to zero to bring the number of samples up to the new, higher > > number of samples. This naturally creates aliases of the original > > audio data. By properly filtering the new file, we end up with a > > higher sample rate file whose audio information is an excellent > > approximation of the original flie. > > > > In the case of this test, the 44 KHz input data is upsampled to 176 > > KHz by means of zero filling which initially creates 3 aliases of > > the input data. The 44 KHz low pass brick wall filter which is > > implemented at a 176 KHz sample rate is supposed to knock out the 3 > > aliases leaving the original data clean and pure. If it is designed > > well, then all is well. > > > > This test is about what constitutes a well designed 44 KHz filter > > operating at 176 KHz. It is supposed to be inaudible.
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