From: gmw1@cunixa.cc.columbia.edu (Gabe M Wiener)
Newsgroups: rec.audio.pro
Subject: Re: The Emperor's new A/D converter
Date: 16 Oct 92 03:56:47 GMT
Article-I.D.: news.1992Oct16.035647.14178
Reply-To: gmw1@cunixa.cc.columbia.edu (Gabe M Wiener)
Distribution: rec
Organization: Columbia University

In article <TONYB.92Oct15155352@titania.juliet.ll.mit.edu> tonyb@juliet.ll.mit.e
du ( Tony Berke ) writes:
>
>1) Do you *really* hear a difference (between it and a reasonable
>   A/D in a DAT deck), or not?

Well, that depends what you call a reasonable A/D.  Certainly it is
not difficult for even the uninitiated to hear a difference between
the A/D of a Strasser or Sony D3 to an Apogee or similar A/D.  One
must be more attuned to the differences between, say, the internal A/D
of an SV3700 and an SV3700 used with an external A/D.

I find A/D's show themselves most on low level material, thus only the
right material will allow the differences to become apparent.  Many
people like to use external A/D's as insurance against discovering
that their program material makes A/D flaws apparent.

Besides the above, I use an outboard A/D (A Pygmy AD-1) for another
reason.  I do location recording.  I don't *want* to have to schlepp a
Panasonic SV-3700 with me.  My Pygmy is a 1U device, so I can come out
of, go through an FC1 box to set up the bitstream however I want, and
then go into a couple of portable machines without worry.

Portable A/D's have always scared me.  You've got a box the size of a
hardcover book (or sometimes a paperback :-) that has to contain your
transport, battery, level meters, preamps, A/D, etc.  I've always felt
that the most important sections, the preamp and A/D, are best left to
designers who had nothing to concentrate except perfecting these
components.

>2) Do you feel that the difference was worth the cost, when compared to
>   spending an equivalent amount elsewhere in the signal chain?

Depends on what the rest of your signal chain is going to look like.  If
your setup consists of two AKG C-1000's and a Strasser, I'd say hold off
on your A/D and invest in some better mics.  If you're using high-end
condenser microphones and if your interest in recording is more than
cursory, then I have no trouble recommending the purchase of a good
A/D.

>The unit I was looking at had some interesting features, most notably
>a built-in soft and hard limiting circuit.
[stuff deleted]
>lack of the occasional clipping (during applause, overenthusiastic
>musical passages, etc) will be *clearly* audible.

Indeed, but that's not the reason to get a converter.  I tend tun
levels conservatively.  I like to average out about 12 dB below max
unless I know for damn sure that the levels are not going to jump.
As you said, if all you're after is limiting, then indeed you could
get a box from Urei or Aphex and do that for less money.

>The salesdude in the store played me a DAT tape that he claimed showed
>a "dramatic" difference when the Apogee was used. He said that the
>main difference was to be heard as a "tightening up of the bass".  The
>tape was prepared by playing a track off of a CD through the analog
>outputs of the player, and then into a Sony PCM2300 DAT's analog
>inputs.  Then the process was repeated using the Apogee and the 2300's
>digital inputs.  I listened to the two selections through the pro
>version of Sony's MDR-V6 headphones, amplified by the built-in phone
>jack in the 2300.

Well, I would never go back to that store again, because they obviously
don't know the first thing about professional audio.

To do a real comparison you need a *good* source, such as a high quality
analog tape, or an analog output of a digital machine playing a tape
digitized and reconverted with equipment at least as good as what you're
testing.  More importantly, the playback levels must be matched *exactly*
and I mean less than a 10th of a dB.  Last, you must do the test using
playback equipment capable of realizing the resolution of the converter.
A walkman won't do it.  A good set of loudspeakers may.

Ideally, you should test a converter where you plan to *use* it.  If you
record live stuff, take it out in the field.  Mult the output of your
preamp.  Take one output through the converter and to a DAT machine, and
take the other just straight into another DAT.  Take the tapes into your
monitoring room and compare them critically.  If you do studio mixdown
to DAT, it's even easier.  Mult the mixdown bus, put a dual-trace scope
(or a VTVM, or transistorized meter with a high input impedance) across
both of 'em and match levels, and print two tapes.

>After the test, I was thinking, "gee, is this guy going to think I'm a
>complete nitwit because I'm going to tell him I heard absolutely no
>difference, execept for the two or three dB of extra recording level
>used during the Apogee selection?"

No, but without even knowing this guy, I can tell him that he should go
back to Audio 101 for a few brush-up classes...

>This was an absurd way to try to demo the product.  I imagine that
>some sort of test using live material, two decks, and careful level
>matching might allow for some sort of meaningful comparison.  Would
>anyone care to suggest a more convenient method, preferably one that
>has yielded audible differences between coverters in actual use?  I'm
:>sufficiently skeptical at this point that I'm not sure that to
>arrange for a weekend loaner, so it would be nice if something using
>prerecorded material could be devised.

Sure, a test could be set up with prerecorded material.  I've always wanted
to do a side-by-side test of A/D's and D/A's, but have never had the time
or the energy to put one together.  Want to come to New York and we'll do 
one? :-)


--
Gabe Wiener - Columbia Univ.     "This 'telephone' has too many shortcomings 
gmw1@cunixa.cc.columbia.edu       to be seriously considered as a means of 
N2GPZ in ham radio circles        communication. The device is inherently of
72355,1226 on CI$                 no value to us." -Western Union memo, 1877
Newsgroups: rec.audio.pro,rec.music.makers,rec.music.synth