[linux-audio-user] Re: 192kHz

Gene Heskett gene.heskett at verizon.net
Sat Jan 28 11:39:27 EST 2006


On Saturday 28 January 2006 08:11, Wolfgang Woehl wrote:
>fons adriaensen <fons.adriaensen at skynet.be>:
>> On Sat, Jan 28, 2006 at 01:30:54AM +0100, Esben Stien wrote:
>> > One big reason for going up to 96kHz is not primarily
>> > because of being able to sample high frequencies, but
>> > because you don't need such a sharp filter at the input
>> > that may taint your input signal.
>>
>> Again very true. The main reason why some people can hear a
>> very very subtle difference between 48 and 96 kHz seems to
>> be that it's quite difficult to make a 'perfect' filter for
>> 48 kHz, even digitally. There are very few DACs that get
>> this right (e.g. Apogee, and you pay for it).
>
>Ok, filter quality. Esben, Fons, on another aspect of
>samplerates higher than 48k: Is it possible that what is
>audible from an orchestra for example stems in part from
>interference or intermodulation of harmonics from above the
>audible band? Relevant for the reproduction had the
>performance been recorded to discrete channels?
>
>I don't know how to phrase my question better. Gene said Yes
>to that if there was "something non-linear in the mixing
>process". I didn't understand that though.
>
>Wolfgang
To elucidate a wee bit, my comment was meant to be refering to mixers in 
the electronic sense.  Mixing products of just two tones will contain 
each signal, and the sum and difference frequencies of them will be 
determined by the amount of non-linearity in the mixer.  Trade the term 
non-linearity for distortion and it might become clearer.  In audio 
work, the target is of course no distortion, but getting rid of that 
last .1% is what you spend unseemly amounts of money on, and play 
pissing matches as to what method is better, yadda yadda.  Of course in 
receivers, the so-called local carrier is driven into the mixer quite 
hard so the resultant output contains as much of these sum & difference 
frequencies as possible.  And then we filter for the sum, or the 
difference, and use that as the intermediate frequency of the classic 
superheterodyne receiver.

However, one tends to forget that the ears own response also generates 
its own distortion, primarily because the amplitude vs loudness is 
fairly close to an inverse square law function for single tones, and is 
why the db was invented all those years ago.

Put the human ear into a multitone situation, and there can be some 
detected distortion/aliasing heard even for tones coming from two 
completely independent amplifier/speaker setups where there shouldn't 
be any interaction between them.

I'm of the opinion that those folks who can lay claim to a golden ear, 
either don't have as much of this effect in the first place, or their 
ears have trained themselves into totally ignoreing that portion of the 
distortion which is ear generated.  I was once such, 50 years ago, but 
alas, at 71, tinnitus has set in and while I can still hear bad audio 
quicker than many younger folks, it is not as nerve wracking as it used 
to be.  One could say I've developed a tolerance for it I guess.

But, because I have been a broadcast engineer, now almost retired, for 
much of my working life, I still need to hear when things aren't right, 
so I can fix them before those emails start coming in. :-)

-- 
Cheers, Gene
People having trouble with vz bouncing email to me should add the word
'online' between the 'verizon', and the dot which bypasses vz's
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.


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