[linux-audio-user] Re: Digital Fidelity

[Gene Heskett]

On Monday 27 February 2006 14:08, Cesare Marilungo wrote:
>Maluvia wrote:
[snip some hocus pocus]
>>There are others - professional audio engineers - who also hear these
>> kind of differences, but I guess they must all be into metaphysics,
>> hocus-pocus and self-delusion as well. (A lot of money in that.)
>>Here are a few articles that touch on this subject, and say a lot of
>> what I have been saying:
>>
>>http://www.johnvestman.com/digital_myth.htm
>>http://www.johnvestman.com/digital_myth2.htm
>
>Thanks for these very interesting links.
>
>It's clear. Files copied from the firewire hard drive sounds warmer.
>It's because of the fire in the wire.

Oh my gawd, yet another generation of ears that claim to be golden.  
Fire in the wire my a$$.

As more of a computer type than musician, and a broadcast engineer for 
41 years & 55 years of chasing electrons for a living, allow me to 
comment that with the data checking and correction done in file systems 
and the drives themselves, if there is a difference between what you 
put into that file, and what you get back from that file, then there 
are uncorrectable errors in the hardware, and both the drive and the 
firewire interface should be screaming bloody murder in the logs, or 
possibly even in your face.

>But you're adviced to backup your sessions anyway, cause the quality
>loss is "very very very slight".

Its .00000000zilch from modern hard drives, unmeasurable.  Not one bit 
can change else the drive does re-reads until it gets a good checksum 
on that sector, and then it hands the data back up the cable.  And not 
before unless it has exhausted its retry limits.  And such an error 
will usually be the subject of an extensive background process to 
recover a good version of that data, write it to a spare sector, and 
remap the access so it gets that spare sector instead of the original.  
And they will do this till they are out of spare sectors.

Aged cd's now, that could be another story as even fresh burns will 
probably be making use of the error corrections inherent in the drives 
own error correction routines that are resident in the drive when its 
played back just to make an sha1sum (or md5sum in older softwares) of 
that data.  Thats just the nature of the media.  There is no concept of 
spare sectors in the cd, so the error correction done is extensive.

Another application comes to mind where error corrections can be 
killers, and thats in video servers.  They don't have the spare time to 
do all those re-reads because they'll have a data under-run while they 
try with pixelization and stuttering of the motion quite plainly 
visible.

Because hard drives can suffer from multipass erasure just as tape can, 
those commercials stored on hard drive arrays have to be re-recorded at 
intervals of about 500-1000 passes, which for a popular commercial 
might occur in as little as 90 days.  So we do keep a cd version of the 
files, and should the copy on the server start to go away like that, we 
just ftp the file from the cd back to the server for an automatic 
overwrite to refresh the file.

Have any of you audio folks encountered mutlipass erasure thing on your 
audio files yet?

>:-)
>
>//
>
>>(There's tons more great stuff on his site w/re to mastering - a real
>>wealth of valuable information - highly recommended.)
>>I have found that his perceptions regarding audio quality closely
>> mirror my own, and his writings have validated much of what I was
>> already hearing. What John and I share in common is having started
>> out as musicians - we were both violinists.
>>Doubtless that has a lot to do with why we hear things similarly - or
>> I might say - *listen* to things in the way we do.
>>Violinists have to train themselves to listen very carefully to
>> things that perhaps other instrumentalists do not.

My wife plays the cello, so one of these days I'll record it straight 
and see what if any diffs I can hear.  When well exersized, thats one 
sweet cello, but if it stands in the case for a month, yeech.

[...]

-- 
Cheers, Gene
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.