[time-nuts] from Sputnik to CD

David McGaw david at endor.com
Mon Oct 8 14:04:48 EDT 2007

As one who has worked in the pro digital audio field for years, I can 
tell you that sub-100 ps jitter very definitely can be heard, 
depending on its spectrum.  Modern sigma-delta ADCs and DACs use 
oversampling clocks of 12 to 50 MHz for sample rates of 44.1 kHz to 
192 kHz at 24-bit resolution and achieve SNR and DNR of 120 dB or 
better, integrated over the audio range.  The noise floor can be -144 
dB or better and a 1-bit signal can be discerned.  Higher-end 
consumer gear do use these as well as pro equipment.

David McGaw

At 12:48 PM 10/6/2007, you wrote:

>I have paid my dues in the HiFi world, but I have always insisted that
>there be a solid scientific basis for any product I bought.
>When faced with claims that picosecond jitter can be perceived by
>the human ear, my flim-flam-o-meter blows a fuse.
>A 1 nsec phasemodulation of a 44100 kHz clock signal will, worst
>case, come out to an noise component 87 dB below the intended signal:
>         1/44100 [Hz] = 22.675 [uS]
>         22.675 [uS] / 1 [nS] = 22675 [ratio]
>         20 log(22675) = 87 dB
>And that is even assuming that the two relevant samples have
>opposite signs, an impossible situation according to the Nyquist
>I find such hifi-nut claims particularly ridiculous, considering
>that every single loudspeaker on the market is designed in defiance
>of how electromagnetism works.
>All amplifiers and loudspeakers on the market are designed assuming
>that the task is to hold the voltage across the speaker terminals
>proportional to the desired sound signal, despite the fact that
>the magnetic field induced in the speakers coil is proportional
>to the current, not the voltage.
>Who in their right mind will claim that they can hear a distortion
>of -87dB, on speakers designed contrary to Maxwells equations ?
>And do I need to mention that very few rooms sport a S/N better
>than about 50 dB these days, and that requires you to turn the music
>up so loud that you are waaaay out of your ears most sensitive
>range ?
>I'm totally with Randi.org on this one.
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