[LAU] Pro Audio? OT rant.

Florian Paul Schmidt mista.tapas at gmx.net
Sat Dec 29 20:54:43 UTC 2012

On 12/29/2012 01:47 AM, Jörn Nettingsmeier wrote:
> On 12/28/2012 03:50 PM, Chris Bannister wrote:
>> I am referring to the faithfulness of the reproduction, when
>> comparing analogue to digital. On paper, an analogue signal is an exact
>> reproduction whereas a digital signal is, by its very nature, an
>> approximation of the original, even if it is very close.
> chris, i love my vinyls, but this argument is as old and tired as it 
> is wrong. any medium this side of the river jordan is band-limited, no 
> matter whether it's analog or digital.

This is true. And not also is it bandlimited, but also introduces 

> the evil little steps in a digital pcm stream are just an upper band 
> limit, and they are _low-pass_filtered_ on playback, which makes them 
> into a time- and value-continuous signal, i.e. analog.
> if you think your lps give you some ultrasonic revelations, measure 
> again, and again after playing them ten more times. if the magic were 
> in the octave from 20-40khz, then every lp would be a disposable "use 
> once" medium. the frequencies below that are reproduced _perfectly_ by 
> a cd.

Playing the devil's advocate here..

Not true. There's also quantization error due to each sample being 
represented as a discrete value from a set of 2^16 values in the case of 
a CD. Shannon's sampling theorem requires afaict that the samples are 
from the set of the real numbers.




What makes digital systems so attractive is that both the bandwidth and 
quantization error are easier to control than the typical limitations a 
purely analogue system has. If your system has too little bandwidth then 
increase the sampling frequency. If it has too much quantization noise, 
increase the bit depth. A vinyl record and a physical record player have 
so many hard to control limitations that it's just cheaper (much 
cheaper) to get a sufficiently good reconstruction ability with a 
digital system.. Needles have mass, they are non-rigid, the vinyl is 
elastic, the speed of light is finite, etc. pp.. In the end a digital 
playback system needs a D/A which is again an analogue system. But still 
it's cheaper to get it good enough (testably) with a digital system and 
a quality D/A than a purely analogue chain.

Have fun,

Florian Paul Schmidt

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