My brief experience with IRENE (2D) supports all of Mason's assertions.
The bottom of a lacquer groove is often malformed because the cutter may be worn or not at the ideal temperature. After cleaning, I often see lacquer groove bottoms that are rounded or rough. This is yet another characteristic of lacquers that pose a challenge to IRENE (in addition to secondary reflections from the substrate, and 2D representation of a 3D groove).
Shellacs have nice flat bottoms and a distinct transition between groove wall and bottom because I believe there's a step where the stamper is polished, making the rough and rounded groove bottom of the master, flat.
Interestingly, we ran a fair amount of tests with an ELP Laser Turntable, and got reasonable real-time playback. The best part of the ELP was its lack of mechanical resonance and lack of tracking error (linear tonearm, if you will). It was still a bit noisier than a stylus and more sensitive to disc cleaning, but the other qualities (lack of resonance and error) made for a compelling listening experience. In our tests, less than 50% of lacquers could be played, and they needed to be relatively pristine. Shellacs were quite noisy because the shellac compound results in a somewhat rough groove wall in comparison to lacquer and vinyl. Dynamic range with the ELP seemed to be less than a stylus, but we didn't measure this at the time.
If you search this forum, I believe you can still find my original posts on the ELP Laser Turntable tests.
On Nov 18, 2015, at 11:22 AM, Mason Vander Lugt <[log in to unmask]> wrote:
Hi all, as I said in the other IRENE thread today, I was the IRENE operator
at NEDCC from the project’s start in fall 2013 until August of this year.
I'm realizing my time to speak as an IRENE 'expert' is limited and passing,
so I want to take this opportunity to share my perspective about the system
and answer any questions any of you might have.
The point I really want to make is that at this point in its development
IRENE is great for the work only it can do (broken, fragile, obsolete) but
not ready to be considered as an alternative for materials that can be done
on a turntable or Archeophone (etc.)
It seems to me the decision of whether to use IRENE or stylus hinges on
three factors - audio quality, throughput/cost and risk of damage/wear.
LBNL, IU Bloomington and NEDCC are currently planning to compare the audio
quality of IRENE’s 3D capability for cylinders against the Archeophone. I
know they’ve worked hard to design a thorough and objective test, so I’ll
defer talking about this side of the system until their tests are concluded.
I would like to talk about the quality of IRENE’s disc audio, though. I
wasn’t permitted to arrange comparative testing in my time at NEDCC, but in
the few examples I could access where clients had separately arranged both
IRENE and stylus transfers, the stylus-based audio was unequivocally better.
This was partially due to the difficulty of imaging lacquer discs (different
surface and groove profile characteristics than the shellac the system was
designed around) and partially due to imperfect image to sound algorithms. I
can only speak to my own experience, and don’t want anyone to take my word
for it, but I think this needs to be formally tested, and any needed
improvements made, before anyone considers using IRENE for intact lacquer discs.
Stylus methods also have the advantage in terms of throughput and cost. In
the best case, IRENE takes 40-60 minutes to transfer a cylinder, depending
on size, and 40-60 minutes per disc side. Stylus transfer, of course, is
usually more or less real-time for intact materials.
With quality and cost favoring traditional methods, the argument for IRENE
really depends on the risk to carriers of traditional playback. IRENE’s
non-contact approach seems to give it a clear advantage in this respect, but
I want to consider this too. David and Rebecca’s presentation at this year’s
ARSC conference made a compelling case that modern stylus-based playback of
cylinders doesn’t cause appreciable wear. I don’t think anyone would make
this case for lacquer discs, but I don’t know how much stylus wear affects
audio quality. Is there research on this? Or would anyone like to share
their experience? Finally, I think it’s worth considering that in IRENE’s
current form, carriers must be transported to Berkeley CA, Washington DC or
Andover MA, presenting a risk that should be weighed against the risk of
wear, especially if turntable/Archeophone transfers can be done locally.
I've heard people say that the current audio quality isn't important because
the same images can be used in the future as the analysis software improves,
and I don't think this is true for 2D (discs) or 3D (cylinders). The 2D
imaging doesn't capture information from the groove walls, which any
engineer can tell you is the part of the groove with the best sound
information (the bottom collects dust, the top becomes scratched). The
current 3D imaging sensor can't capture high enough resolution in the
vertical domain to derive audio to current archival standards (the vertical
resolution of the image translates into the bit depth of the audio). David
Giovannoni wrote up the most complete analysis of this issue that I've seen
yet, and I encourage him to share it.
I’m sorry if this seems insensitive or unnecessary, but I know people want
to know where the system stands, and right now the information is
privileged. I think IRENE deserves all the good publicity its gotten for the
materials only it could do, and that it has a lot of potential for a
continuing and expanded role in audio preservation, but I also think that it
needs to be held to a higher standard if it's going to be considered as an
alternative to existing methods, and it's simply not ready yet.
Thanks all for putting up with my rant. Please let me know if you have any
questions, and I'll do my best to answer them on/off list as appropriate.
Mason Vander Lugt