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Time resolution of digital sampling


Don Hills

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There wouldn't be a problem with "intersample overs" if the people mastering the track did their job properly - trivially easy to test whether it could occur, and then just attenuate the level enough so that at the time of the reconstruction of the analogue, it's guaranteed that the maximum level is never exceeded.

 

A 'smarter' DAC could use a sledgehammer approach, and just digitally attenuate the signal by say 3dB before converting, to ensure there is never a problem ... it's a silly issue, which can be undone - but someone has to do it.

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  • 7 months later...
Quote

 

Tell me what the theory is exactly if you have any idea?

 

The reason we have 18-22 kHz upper limit is based on the anatomy of the cochlea and hair cell response to single tones. This does not extrapolate to an arbitrary pattern of frequencies at arbitrary volumes and phases (nonlinear response) nor does that extrapolate directly two two cochlea with differential signaling.

 

 

All the things that Paul is pointing to ... while the ear "in perfect shape" may be capable of registering those very top frequencies, in the sense that one is conscious of a difference when those frequencies are present, as against not being present - in the real world of live music, and how sensitive the older person, the one who is usually most interested in the subtleties of the texture of the sound, is to those aspects, it is such low importance that it doesn't bear worrying about ...

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What people are really worrying about, is whether some 'magic' can be generated in the replay, if frequencies above 20kHz are 100% accurately reproduced ... well, the answer is, No!!! ... and, yes, this is very much so a subjective position, in an 'objective' thread, 😜.

 

The listening brain adjusts for bits "that are missing" - automatically ... I just saw yesterday, in one of the papers, that the experimental results were thrown, when people listened to replay with ultrasonics missing, directly after hearing the same track, with. The listeners had 'learnt' what the ultrasonic content was doing, and unconsciously added it back in, when it was no longer there - and couldn't distinguish the two versions any more ... unfortunately, the ear/brain is too clever for us poor inquiring sods - it will always outsmart us ... 😁

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1 hour ago, Jud said:

My own interest lies more in the area of what sort of sampling rate is appropriate to capture audible inharmonic attack transients present in music. (As I think @PeterSt said, pretty much everything in music has an (inharmonic) attack phase.) "Inharmonic" doesn't mean non-periodic, it just means one needs higher harmonics to reconstruct them. And that's the reason for my interest in whether very brief sounds are audible.

 

Just to note that attack and inharmonic are very different things - the piano has as high an attack as any instrument out there, but its inharmonicity is relatively low. Cymbals are an example at the other end, where attack is basically noise from the metal being struck, which then becomes inharmonics of the metal ringing in a complex fashion.

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  • 2 weeks later...
1 hour ago, Don Hills said:

 

Personally, I don't spend much time worrying about them. By definition, an intersample over occurs between 2 samples. Therefore, its frequency content is above 22 KHz. Provided that the DAC clips cleanly and the ultrasonic content doesn't upset the following equipment, it should be inaudible. (Of course, in real life things are rarely that ideal.) But I'd still rather see them avoided at source than having to allow for them in playback.

 

What??!!  An intersample over is above 22kHz? ... A trivial, manufactured example of what can happen, at say 11kHz,

 

https://i.imgur.com/odM1Iuq.png

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The first example I posted above I just grabbed from a quick search of images ... but note that a comprehensive overview was done by @Archimago , http://archimago.blogspot.com/2018/09/musings-measurements-look-at-dacs.html. And specifically he notes what can occur with, as examples, fs/4 and fs/6. Here the simple, potential HD is well and truly in the audio range - and a real world DAC does make a mess of it.

 

Also note that he points to a discussion of worst case scenarios ... https://hydrogenaud.io/index.php/topic,98753.0.html.

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