On 13/08/2015, Peter S <peter.schoffhau...@gmail.com> wrote: > > Bonus experiment: try to see if you can hear the difference between > sine_fadeout16_noise.wav and sine_fadeout8_noise.wav in a blind ABX > test. If not, then having extra bits of noise make zero sense.
I did a blind ABX test between them. Despite both signals have a -36 dB noise floor, I could discern the difference, the quantized signal sounding slightly more noisy. I examined the noise (quantization error) in detail. Here is how it sounds like: http://morpheus.spectralhead.com/wav/quantization_noise.wav This is 1-bit of white noise, which is the quantization error. Its spectrum looks entirely flat: http://morpheus.spectralhead.com/img/quantization_noise_spectrum.png The "bump" at 0 Hz is caused by a DC offset, since it was truncated and not rounded, so the error is not symmetrical between -0.5 .. 0.5 bit, but is rather between -1 .. 0 bit. The waveform - when normalized to 0 dB, looks entirely like white noise: http://morpheus.spectralhead.com/img/quantization_noise_waveform.png Its spectrogram also looks like white noise - there are absolutely no harmonics or signal-related artifacts, it looks like fully uncorrelated, pure white noise: http://morpheus.spectralhead.com/img/quantization_noise_spectrogram.png The amplitude of the error is 1 LSB, which - in the case of 8-bit quantization - means -42 dB amplitude. Since 42 dB is a small SNR, I could discern the difference in blind ABX tests, though the difference is quite minor (do an ABX test yourself to hear yourself). If the quantization were to 24 bits instead of 8 bits, the amplitude of the quantization error in a similar situation would be -140 dB (= 1 LSB at 24 bits precision). That is absolutely beyond both every soundcards' dynamic range, and the human hearing's dynamic range. Since discerning the difference in a signal quantized to 8-bits was already not trivial and needed careful listening, I am absolutely 100% convinced that the difference in a 24-bit signal would be absolutely imperceptible in a blind ABX listening test under ideal listening conditions with the most high-end gear available. Therefore, based on two different tests, I still hold my original opinion that having extra 8 bits of noise in a properly dithered converter beyond the 24th bit is absolutely useless, and makes absolutely zero practical difference. There is not even a single soundcard on the planet that could even properly reproduce signals with -140 dB amplitude (most high-end ones have an SNR of only around 115-127 dB), therefore this couldn't even be properly tested. And even if there were an equipment capable of such precision, it is already beyond the dynamic range of the human hearing, which is around 120 decibels (excluding signal levels beyond the pain threshold), beyond which, the signal is perceived as noise-free. If it's already "noise-free", there is no way of getting any better than that... -P _______________________________________________ music-dsp mailing list music-dsp@music.columbia.edu https://lists.columbia.edu/mailman/listinfo/music-dsp