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Audibility of 20kHz brick wall filtering, samples provided for ABXing - 24/96 sound card required
post Jan 8 2009, 17:30
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This test continues the discussion in this thread...


...using the impulses provided at the end of that thread as filters.

I've filtered some 24/96 audio with the linear phase (050) and maximum phase (100) 20k impulses, and uploaded the results here:


The "reference" is just the original convolved with an impulse, i.e. a null operation.

All files are 24-bit 96kHz sampled .wav files. You will need a 24/96 sound card to listen to these files, and use something like foobar2k which plays the files properly.

The "reference" should sound best, the "maximum phase" file should sound worst. Can anyone ABX a difference?

(I don't claim to be able to hear any difference).

btw, the files are time aligned to the nearest sample, though the maximum phase filter introduces a sub-sample delay and slight phase shift. I've confirmed that all low pass filters have identical amplitude responses, and that the pass band of the low pass filters matches the level of the unit impulse. Source: Cool Edit Pro frequency analysis, 65536 FFT, Linear View, Range 24 dB, Reference -90 dBFS, window expanded to fill my screen, absolutely no different between plots.

In the last second end of each audio file is a unit impulse, filtered - hence the filter itself is "included" in the file, for easy checking, analysis and verification.

(I used Cool Edit Pro to do the convolution (filtering). I'm not entirely convinced by its algorithm - there are some errors 100dB below the signal, verified by convolving with a single impulse. From the nature of the errors, I assume it's performing time domain convolution by frequency domain multiplication, which is quite common, and there are some rounding errors which would be lost in the noise of a 16-bit signal, but are apparent with the 24-bit signal)


P.S. When I tried to FLAC encode these files (using FLAC 1.2.1b in Windows XP), the FLAC verifier from the same package (not the one called automatically when encoding, but the stand-alone one) reported errors, hence I've provided .wavs instead. I hope my system isn't on the way out - can anyone else reproduce this problem?
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post Jan 15 2009, 22:20
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I, probably like most people here, can't hear a whit above 18k to begin with. So I'm not even going to try. wink.gif
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