[time-nuts] Re: High precision OCXO supplier for end costomers

[Stefan Heinzmann]

Am 10.01.2022 um 20:05 schrieb Attila Kinali:
> On Mon, 10 Jan 2022 19:19:09 +0100
> Stefan Heinzmann <stefan_heinzmann at gmx.de> wrote:
>
>> Yet you mention phase noise specs very close to the carrier (so close
>> that any artifacts are bound to mix into the subsonic range!),
>
> A word of caution here: Human hearing is very very sensitive to some
> things. One of those is two-tone discrimination. We can tell two
> simultaneous tones appart quite easily, even if they are very close,
> given they are at about the same loudness. 10Hz difference is nothing
> and everyone can do that, even without training. Only once you get to
> around 1Hz difference, will you need to get a musician or someone with
> an equally trained ear. And it isn't the limit yet of what we found that
> people, with training, can hear.

When two tones with approximately the same level and a frequency
difference of 1 Hz mix, you get a flanging effect due to the shifting
phase relationship, and that tends to be very obvious. No need for a
trained ear there.

But that's not what we're about here. Human hearing definitely has its
particular sensitivities, but that only goes to show that you can't make
sweeping generalizations that can be expressed in terms of simple
numbers like the phase noise 1 Hz from the carrier. It is dependent on
the scenario, and one of the questions that needed asking, and was
asked, is: What does the oscillator actually drive, i.e. feed into?
There simply isn't any way to come up with meaningful figures if you
don't have a very clear answer to that question. And the original poster
didn't offer any.

Furthermore, the ear's properties, and those of the entire auditory
system, have been studied in considerable detail. It isn't a big mystery
anymore what we are capable of hearing, and what we almost certainly
aren't. This includes the effect of phase jitter/noise.

> The reason why I am sceptical of the phase noise specs is because
> artifacts would end up at much lower amplitudes. Which means the
> signal that causes the artifact would be so much louder than the
> artifact, that it would mask the artifact.

Yes, masking is one reason why you wouldn't hear artifacts resulting
from phase noise close to the carrier. But the specs offered by the
original poster are so "aggressive" that you wouldn't even need to take
masking into account for dismissing audible effects as implausible.

Cheers
Stefan