[time-nuts] Re: Clock specs for audio (was: High precision OCXO supplier for end costomers)

[Stefan Heinzmann]

Just curious: Do you, from your customer interactions, have the
impression that your customers are equipped to verify those performance
figures? Or do they essentially have to trust you?

Cheers
Stefan


Am 10.01.2022 um 16:12 schrieb Bernd Neubig:
> We are receiving such inquiries from "Audio nuts" rather frequently, but
> also from professional high-end audios-studio equipment makers. There
> argument is often, that the spatial transparency of the sound, i.e. how
> exactly you can locate the sound source (instrument in an orchestra) would
> be noticeably improved by such ultra-low noise OCXO sources. So it should be
> more about time or phase (jitter?) than about frequency....
>
> As the customer and his belief is "king" at AXTAL - as long as doable and
> payable - we have developed our AXIOM45ULN series, where the best phase
> noise option guarantees a PN level of -115 dBc/Hz @ 1 Hz. But this kind of
> performance can only be achieved by a crystal selection with rather low
> yield. Therefore, as a manufacturer you need enough customers who accept
> that "less is sufficient" and will buy the OCXO made from the other
> crystals. We also are getting a few parts with -120 dBc/Hz @ 1 Hz out of a
> larger lot, but we rather keep them than selling them to everybody.
>
> Best regards
> Bernd
>
>
> -----Ursprüngliche Nachricht-----
> Von: Attila Kinali [mailto:attila at kinali.ch]
> Gesendet: Montag, 10. Januar 2022 15:42
> An: Discussion of precise time and frequency measurement
> <time-nuts at lists.febo.com>
> Betreff: [time-nuts] Clock specs for audio (was: High precision OCXO
> supplier for end costomers)
>
> On Mon, 10 Jan 2022 12:35:17 +0100
> Attila Kinali <attila at kinali.ch> wrote:
>
>> That said, are yo sure you need such stringend phase noise requirements?
>> It's audio. Nobody is going to hear whether the noise is -60dBc or
>> -80dBc @ 1Hz, much less -120dBc.
>
> To give here a bit more background: psychoacoustic masking, which is the
> relevant metric here, mans that we cannot discern sounds that are close to
> eachother with one of them being louder than the other. Depending on who you
> listen to, it's usually a sound masking another sound at a distance of 100Hz
> up to 20dB to 40dB lower. Even if we account for someone with golden ears
> and use 60dB, that would translate to a noise spec of -60dBc @ 100Hz offset.
> That's a spec that almost all XO do fulfill. A good VCXO (40-100MHz) is
> somewhere around 90-100dBc @ 100Hz.
> Any OCXO will fulfill that spec too, even the tiny DIL-14 ones (most are at
> -110-140dBc @100Hz @10MHz).
>
> And this doesn't take into account that we are arguing about audio frequency
> specs at HF frequencies. I.e. if we use the 10MHz clock and use it to derive
> a sampling clock for an ADC to sample a 20kHz signal, the noise performance
> improves by another ~25dB... at least (if the design is done right, it can
> be up to 50dB)
>
> What is more important than close in noise, though, is broadband noise
> performance and spurs. For someone with good ears, it's not unheard of to be
> able to discern far away noise and spurs down a -100dB-120dB. Especially the
> spurs can be quite hard to control, depending on what clock synthesis system
> is used.
>
> Another important spec, especially for recording, is accuracy of frequency.
> An offset of just 1ppm becomes 3.6ms if you record for an hour. That's
> something most people can hear already. But whether this actually elevant or
> not depends on how the recording is done. The usual way is to have a central
> master clock that feeds all clocked devices, such that all of them have the
> same notion of time/frequency. In that case, quite high frequency deviations
> can be tolerated, way beyond what a simple XO would deliver.
>
> 				Attila Kinali
> --
> In science if you know what you are doing you should not be doing it.
> In engineering if you do not know what you are doing you should not be doing
> it.
>          -- Richard W. Hamming, The Art of Doing Science and Engineering
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