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ARSCLIST  April 2012

ARSCLIST April 2012

Subject:

Re: analog vs digital eq

From:

Clark Johnsen <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Fri, 13 Apr 2012 22:59:00 -0400

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (179 lines)

Seconding Eric here, so far as I'm competent to. "I would argue that the
3-bit loss is not that negligible." No kidding!

"The dynamics (not the bandwidth) present in a shellac (78) is wider than
you might expect... I agree with Robinson that most of the benefit is in
the bass." The trick I use, is to play 78s on a wide-range,
low-phase-distortion high-end system capable of substantial volume. Here
you can hear what's really in those old grooves, and the results can
compare with LPs and CDs, depending. But especially in the bass. Every
audio system I've heard (far from all of them) in transfer and restoration
facilities pales beside this one, which leads me to wonder how some things
turn out so well despite. Luck o' th' shellac!

clark


On Fri, Apr 13, 2012 at 7:53 PM, Eric Jacobs <[log in to unmask]>wrote:

> 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
> with precision.
>
> 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.
>
>
> Eric Jacobs
>
> The Audio Archive, Inc.
> Disc and Tape Audio Transfer Services and Preservation Consulting
>
> tel: 408.221.2128
> mailto:[log in to unmask]
> http://www.theaudioarchive.com
>
>
>
>
>
> On 4/13/12 8:10 AM, "Doug Pomeroy" <[log in to unmask]> wrote:
>
> >Parker,
> >
> >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
> >instance,
> >taking the RIAA curve there is a lift of nearly 20 dB at 20 kHz so
> >that the
> >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
> >would
> >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.
> >
> >Doug Pomeroy
> >Audio Restoration & Mastering Services
> >Transfers of metal parts, lacquers,
> >shellac and vinyl discs & tapes.
> >193 Baltic St
> >Brooklyn, NY 11201-6173
> >(718) 855-2650
> >[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
> >>> =20
> >>> 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.
> >>> =20
> >>> Also, applying eq digitally to a truly flat transfer reduces
> >>> available headroom somewhat.
> >>> =20
> >>> Doug Pomeroy
> >
>

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