[LAU] Sampling rates [WAS]: Re: jack/oversampling

[Jörn Nettingsmeier]

On 03/16/2014 09:50 PM, Lorenzo Sutton wrote:
> On 16/03/14 19:39, Gene Heskett wrote:
>> On Sunday 16 March 2014 14:25:14 Ralf Mardorf did opine:
>>
>>> On Sun, 2014-03-16 at 08:58 -0700, Len Ovens wrote:
>>>> I would mix the project  at 48k or 96k
>>>
>>> Why 96 KHz? 48 KHz doesn't cause any issues, but already provides best
>>> sound quality.
>>>
>> That I think is a personal call Ralf, primarily because at 48 Khz, your
>> anti-aliasing filters had better be very very good brick walls by the
>> time
>> you get above 24Khz in input content
>
> Can anyone point out a commercially available microphone used in the
> audio recording domain which will actually pic frequencies above 20 kHz?

i once talked to a bat researcher (no joke) who had a simple mod to a 
røde nt5 that would allow it to work reasonably well up to 30k.

earthworks make special versions of their excellent microphones which 
are linear up to 50khz, for those who need it (or think they need it).

in fact, most if not all microphones can do this but for additional 
filters added by the manufacturers to increase robustness in the 
presence of HF electromagnetic noise. the question is how linear they 
are up there, and whether the pickup pattern is still useful. all but 
the smallest capsules can be expected to become highly directional at 
HF. something like a DPA 4060 or a SH MKE-1 might be good experimental 
capsules for ultrasonics.

> Likewise can anyone point out any commercially available speaker used in
> the audio reproduction domain which will actually reproduce frequencies
> above 20 kHz?

most tweeters are easily capable of 30khz, and there are no major 
engineering obstacles to 50khz on-axis.
the big issue is excessive beaming, both on the recording and playback 
side of things.

> If the audio produced is made for fruition of humans it makes absolutely
> no sense to try and capture or reproduce anything above 20kHz, and for
> average individuals 15kHz would probably more than enough.

i'd tend to agree with that statement, but there are very valid reasons 
to do it:
* not all recordings are meant for humans to hear - if you are measuring 
something, you might appreciate results outside of human sensation.
* not all recordings are meant to be heard in its original frequency 
range - talk to any bat enthusiast. seriously, what those guys do makes 
you itch to try 192khz and a microphone that is open "from dc to 
daylight", as the saying goes.
* sometimes, preservation of information is extremely important. for 
instance, there are valid reasons to digitize old analog tapes at 
ridiculous rates (say, 384 kHz): doing so lets you record traces of the 
HF bias, which might help in eliminating wow and flutter artefacts more 
precisely than tracking the 50 or 60hz power grid hum.
or there's a colleague from italy, david monacchi, who records sound 
scapes in soon-to-be-destroyed natural habitats - why would you limit 
yourself to 10 octaves if you can get 11, before the bulldozers arrive? 
(i once heard him lecture on one of his works, and indeed he was using 
sonograms to identify certain species of animals, many of which are 
capable of uttering ultrasonics.)

there is still ongoing debate about indirect audibility of high 
frequency content via transients - i'm not too convinced, but i can 
understand any colleague who would rather record too much today and then 
downsample, as opposed to finding you won't be able to fully exploit 
future distribution formats with your legacy material. if i'm not maxing 
out my equipment in terms of cpu cycles, there is no harm done in erring 
on the side of caution, if high sample rates don't incur higher costs as 
they go through the workflow.

as a counter-example, a tv production i'm involved in uses 96k 
initially, but only because the live sound desk is a midas which cannot 
do less. it is immediately downsampled to 48k before going onto the 
broadcast network via dante, because nobody wants to put up with the 
extra data and doubled loadin/transfer times.

> And in case anyone is tempted to state that even if we don't hear them
> frequencies above 20kHz influence the way we hear or 'perceive' music,
> please also attach any _scientific_ study/paper/evidence (e.g.
> large-scale blind tests etc. not anecdotal evidence) to such statement.

actually, i just had a behringer ada8000 die on me, and i will probably 
replace it with some 96khz capable kit from directout. i don't expect to 
find anything interesting, like you said, but i'm going to try it 
nonetheless. i know that my tweeters will only begin to roll off at 40khz.

i'm not advocating high sample rates, but hey, "because i can" has 
always been a strong incentive :-D
the main problem is that some equipment actually gets worse at high 
sample rates, and putting a 192k sticker on your box is actually more 
important than getting 48k really right...


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