[time-nuts] from Sputnik to CD

Henk ten Pierick henk at deriesp.demon.nl
Sat Oct 6 07:27:17 EDT 2007

On Oct 6, 2007, at 3:01, Magnus Danielson wrote:

>> If the sample rate is 44.1 kHz then the adev below 1 s, even
>> down to 10 us, or jitter, or the phase noise above 1 kHz are
>> they key parameters; not long-term drift. In this case I'd take
>> a nice 10811A over a typical Rb any day. Does anyone know
>> for sure, or am I off base here?
> No, I meant to say the same. The phase-noise in the 10-1000 Hz  
> region is
> surely what will mostly affect the sound, so we are looking at side- 
> band
> phase-noise rather than Allan dev plots. However, slow modulations  
> even up to
> a minute is known to be perceptible, but the tolerance levels is  
> not flat.

I think this is correct. Is there a figure in dBc/Hz at say 10, 100  
or 100 Hz.
When measured with a Wavecrest 2075 there is a clear difference in  
hearing between
an oscillator with -100 dBc and -96dBc both at 10Hz. The listening  
difference is in the sound stage accuracy and
acoustics of the concert hall.
I do not have (access to) instruments that measure phase noise  
directly to say -120 dBc at 10Hz.

> If anyone is interested in learning about serious reasoning behind  
> acheiving
> high dynamic digital audio, look up Julian Dunn, who has written a  
> few very
> good papers. He also did work for the AES/EBU jitter limits and  
> also wrote some
> stuff for Audio Precision. Great stuff and a sensible reasoning on  
> these
> things.

Agreed, but Julian does not give phase noise figures in dBc/Hz figures.

> It should be noted that for lower modulation frequencies, the side- 
> band will
> be so near that the ears masking-effect will cancel it out unless  
> it is
> strong, so tolerance levels rises for lower frequencies.

I doubt if this is true. I have never found an agreement to known  
psycho-acoustic masking figures and
own jitter measurements. It is amazing what can be heard with jitter  
values of pico-seconds.
There must be a relation between these low values and something else,  
but I am not aware of it.
The phase noise statement of Magnus can be correct, I think it is,  
but the side bands resulting from
these values are within the masking curves.

Experiments with a modulated clock show that large modulation can not  
be heard. However, noise modulation much smaller can destroy the  
sound stage. I am very interested in a good explanation of this.
I you do not believe me you are welcome for a demonstration.


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