On a high-quality shellac or lacquer, analog EQ makes an audible
difference for the reasons that Doug cites (i.e. Sean Davies).
We've performed extensive tests, and the difference is not that
subtle. We use a high quality Analog EQ plug-in from Cube-Tec
for our Audiocube DAW (64-bit).
In the AES October 2007 R.S. Robinson paper, he states in the
conclusion on page 8 of 8:
"Exceptional, uncommonly encountered program material may cause
a worst case bass truncation of approximately three bits, which
is negligible considering the 24 bit resolution capability of
modern analog to digital converters."
I would argue that the 3-bit loss is not that negligible, and
would add to the end of this sentence "..., but still audible."
For the most part, FLAT transfer with EQ in the digital domain
on many LP discs of average quality will be indistinguishable
from analog EQ (assuming you have a precise analog EQ). And
that's the benefit that Channel D is selling - accurate RIAA EQ.
Many RIAA EQs are not that accurate, with some introducing
intentional changes to RIAA for market differentiation, and
gullible reviewers stating that they hear more air or top-end,
or more bass with one phono preamp versus another. Indeed the
reviewer does hear these things, but that's because the EQ curve
may not be a precise RIAA EQ for that particular phono preamp.
The audiophile world is notorious for inaccurate RIAA EQs. On
the other hand, the RIAA EQ of a low-cost phono preamp may not
be that accurate from a design/manufacturing point of view.
Keep in mind that the human ear has a sensitivity of about
0.1 dB, and it is costly to build an EQ to that level of
precision. On the other hand, the original recording equipment
or disc lathe was not accurate to 0.1 dB. One can argue about
what level of precision is relevant for conforming to an EQ
standard. In my opinion, +/-0.25 dB is the maximum tolerance,
and +/-0.1 dB is desirable so that you aren't stacking up
EQ errors (recording EQ errors + playback EQ errors). I won't
name names, but I've measured $10k phono preamps that have
+/-0.5 dB tolerances, so price does not necessarily correlate
If you have a high-quality phono preamp for LP playback that
has an accurate RIAA EQ curve, I see no reason to playback
FLAT and digitally process the results with digital EQ,
especially if you are dealing with a standard like RIAA, which
is Channel D's core market.
Up to this point, I've been commenting on LPs and RIAA EQ,
the focus of the Robinson paper and Channel D.
The dynamics (not the bandwidth) present in a shellac (78) is
wider than you might expect. I've found that on average, 78s
fair much better with analog EQ then FLAT, and the difference
between digital and analog EQ is not that subtle. I wouldn't
necessarily be a purist about EQ choices - use your ears. But
you can get better results with analog EQ than you can with
digital EQ on many 78s.
I agree with Robinson that most of the benefit is in the bass.
My preferred analog EQ for shellacs and lacquers is a single
turnover Blumlein 500 Hz or 300 Hz curve (depending on the
recording). This prevents the 3-bit truncation and loss of
dynamic range, while giving you plenty of flexibility for digital
EQ for the mid and high frequencies. Best of both worlds.
The Audio Archive, Inc.
Disc and Tape Audio Transfer Services and Preservation Consulting
mailto:[log in to unmask]
On 4/13/12 8:10 AM, "Doug Pomeroy" <[log in to unmask]> wrote:
>The point, made originally by British engineer Sean Davies, was that
>without any high end roll off, the record level would need to be lowered
>somewhat to avoid clipping at the time of A/D conversion: "There may
>be a bit penalty to allow for headroom in the A/D conversion. For
>taking the RIAA curve there is a lift of nearly 20 dB at 20 kHz so
>transfer level would have to be reduced by this amount which implies the
>loss of 4 bits compared with analog equalization." With 78 rpm discs he
>states: "the bit penalty for a constant velocity above 250 Hz curve
>be 2 to 3 bits." His AES preprint is Convention Paper 5534, (2002).
>A reply to Davies is found in AES Convention Paper 7185 (2007), by
>R.S. Robinson of the Channel D Corporation, which advocates flat
>transfers and EQ in the digital domain.
>Gary Galo gave a talk at the 2009 ARSC Conference: "Phase Equalization
>and Its Importance in the Playback of Disc Records", which may be
>heard via the web site.
>Audio Restoration & Mastering Services
>Transfers of metal parts, lacquers,
>shellac and vinyl discs & tapes.
>193 Baltic St
>Brooklyn, NY 11201-6173
>[log in to unmask]
>> Date: Thu, 12 Apr 2012 17:53:59 -0500
>> From: Parker Dinkins <[log in to unmask]>
>> Subject: analog vs digital eq
>> Any time you boost levels the headroom is reduced, whether it be in
>> the =
>> analog or digital domain.
>> If any digital audio program material is too high, 1) reduce the
>> global =
>> level before boosting, 2) cut instead of boosting, or 3) use
>> floating =
>> point processing and adjust the levels when it goes to fixed point.
>> I'm not convinced that analog eq is always desirable with disk =
>> transfers; I know the arguments pro and con. It is very helpful to
>> have =
>> a high quality phono preamp with a variety of curves for quick
>> reference =
>> in auditioning a disk.
>> Parker Dinkins
>> On Apr 11, 2012, at 11:00 PM, ARSCLIST automatic digest system wrote:
>>> Date: Wed, 11 Apr 2012 16:28:26 -0400
>>> From: Doug Pomeroy <[log in to unmask]>
>>> Subject: analog vs digital eq
>>> I think the short answer is that the recording curve was
>>> imposed in the analog domain, in reversing it for playback,
>>> only analog eq handles the phase response correctly.
>>> Also, applying eq digitally to a truly flat transfer reduces
>>> available headroom somewhat.
>>> Doug Pomeroy