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On Wednesday, March 10, 2010 7:25 PM, Parker Dinkins wrote:

> As a logical progression, click removal before imposing the 
> RIAA playback curve significantly improved in the click 
> detection process because the RIAA playback curve reduces 
> high frequencies.
>
> With modern tools, transferring flat, removing clicks, and 
> then imposing the RIAA playback curve is not as essential to 
> the click removal process as it once was - but it's certainly 
> the conservative and correct approach for archival work 
> because we don't know what further developments will occur
> with digital technology. And it doesn't hurt in the click 
> removal process.

I'm still wondering if the best results are achieved with bass
EQ and flat treble EQ.  The bass EQ guarantees that there is 
no word length loss in the bass, and retains all the impulse
noise information untouched in the treble for noise reduction.


> Back to the main point: the conclusion of R.S. Robinson in 
> my previously cited 2007 AES Paper 7185 was that in most 
> cases the bass resolution truncation was 1 bit or less, which 
> is negligible in light of the 24 bit resolution capability 
> of modern converters, and in all events is more than compensated 
> for by enhancement in the higher registers, where aural acuity
> is greatest (like those Fletcher and Munson boys described).

It's worth noting again that the R.S. Robinson paper is entirely
based on the analysis of vinyl LP media.  In particular, a great
deal of analysis and characterization of the high frequency 
balance found in LPs is made as part of the assumptions of that 
paper.  Pre-vinyl media has dramatically more high frequency 
noise in the form of crackle, clicks and pops than vinyl.

It may be worth mentioning that I participated in tests of
the Channel D Pure Vinyl software EQ with 1940s shellacs, 
and there was clearly a loss of dynamics with the digital EQ 
when compared with the analog EQ.  Clear in that everyone who
participated in the test could easily identify analog versus
digital EQ.

It was this test that started my quest as to "why" there 
was such a notable difference between analog and digital EQ, 
and is leading me to question if FLAT archival transfers for 
pre-LP media really make sense?  Are we actually losing important 
audio information with FLAT transfers of pre-LP media that 
cannot be recreated with digital tools?  Are bass dynamics 
getting quantized away forever with FLAT transfers of pre-LP 
media?

FLAT transfers for pre-LP media is a "best practice" that 
might be worth re-visiting.  I don't think full analog EQ
is the right answer for preservation either.  There may be
a logical middle ground - bass EQ (to prevent word length
loss in the low frequencies) and FLAT treble EQ (to preserve
transients for noise reduction).

No doubt, high performance analog EQ is very expensive.
Digital EQ can be quite cost effective in comparison - with
some minor compromises for LP media - and I think that's the 
case Channel D are trying to make (that the benefits of 
digital EQ outweigh the detriments).  Digital EQ is certainly
a valid approach.  But I'm not sure we fully understand the
compromises we are making with FLAT transfers and digital 
EQ on pre-LP media.

Eric Jacobs

The Audio Archive, Inc.
tel: 408.221.2128
fax: 408.549.9867
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http://www.TheAudioArchive.com 
Disc and Tape Audio Transfer Services and Preservation Consulting