[time-nuts] from Sputnik to CD
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.
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
>I'm totally with Randi.org on this one.
>Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
>phk at FreeBSD.ORG | TCP/IP since RFC 956
>FreeBSD committer | BSD since 4.3-tahoe
>Never attribute to malice what can adequately be explained by incompetence.
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.
More information about the time-nuts