From: kurt@tc.fluke.COM (Kurt Guntheroth)
Subject: Re: Too much lossy encoding?
Keywords: PASC, audio
Reply-To: kurt@tc.fluke.COM (Kurt Guntheroth)
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Date: Mon, 13 Apr 1992 21:22:22 GMT

I want to clarify some things I've said in light of the discussion that has
ensued.  

The following things concerns me about lossy encoding 
1.  People are "lowering the bar" for what is acceptable signal loss.  The
    goal of CD encoding (which is only lossy in the Nyquist sense) was to
    obtain about the same fidelity as an ideal phonograph record.  I have
    recently seen the PASC scheme compared to the quality of FM radio
    reception.  It is my opinion that people are focusing more strongly on
    how mush loss will fit the program material onto the storage or
    transmission medium than they are on how much loss is, in fact,
    imperceptible.
2.  A given digital encoding scheme generally defines a single level of
    quality such that if you can decode the signal at all, you get that
    level of quality and no more.  Another way of looking at this is that
    the transmitter/encoder of a digital signal makes all the decisions
    about the quality of the received signal, and no amount of money or
    technology at the receiving/decoding end will improve the quality of the
    signal over this minimum level.  By contrast, in most analog systems,
    a very fine signal is transmitted/encoded, and can be recovered under
    ideal conditions.  The quality of the actually received signal can be
    improved up to a certain limit by spending more on the receiver/decoder.
    This attribute lets the user determine signal quality.
3.  Multi-format formats are only useful if the receiver can understand them
    all, at least to some extent.  If each sub-format requires its own
    receiver hardware, we've hardly improved anything have we?

There exist encoding techniques, like some of the HDTV techniques, that
encode some information at a higher power than other information, so that
signal quality falls off gracefully with distance from the transmitter.
Another example would be a storage format with 20 bits of precision, and a
decoder that could decode 14 bits, or 17, or 20, depending on the needs of
the users.  These digital techniques have the same desirable user-oriented
attribute that the user chooses the fidelity of playback.

On the other hand, many other proposed systems do not posess this attribute.
They fix playback fidelity to conform to the instantaneous market and
technology conditions of a particular day, not to theoretical absolute
limits or traditional limits like available channel bandwidth.

As a consumer I don't want to have to buy a format that will become obsolete
in a very short time as storage density and perhaps transmission bandwidth
increase.  Like the 8-track palyer, which was rapidly bypassed by better
technology, I think such systems may not pay back the investment in designing
them.  As an engineer, I despise the shortsightedness of some of the designs
I've seen described.  As electronic display and playback device technology
advances, the limit of what is perceptible will change.  Setting your sights
too low as a designer will not pay back your investment.

I won't throw out my library of software every five years to upgrade
to a better format.  We all did that once, with records-to-CD's, but we were
told CD's will last forever (remember that?  Now they say maybe 10 years).
I won't do it again soon, and certainly not frequently.  Every little
dead-end compression scheme will make the next one harder to sell, even if
it is better, and especially if it is not.

Here's some questions.  These are the reality checks for claims of
imperceptible signal loss.  This is the test for whether the signal loss is
REALLY imperceptible, or just a hack to fit today's storage technology.

1.  Anybody designing storage formats where the receiver determines the
    fidelity in a non-trivial way?
2.  How long did the 78 rpm phonograph format last?
    How long did the 33 1/3 rpm LP format last?
    How long did the NTSC TV format last?
	Color was added in a compatible way.  Even so it took years for a
	significant number of people to upgrade to color.
    All these formats were replaced by significantly better ones, both in
    terms of ease of use and signal quality.  All these formats improved
    during their lifetime, especially the quality of playback equipment.
3.  How many people will give up CDs for mini disks and digital cassettes
	and MPEG players if the signal quality is less good?  
    When CD-I (or whatever) comes along, and data comes on a thing that
	LOOKS like a CD, what will be users reaction if audio data doesn't
	SOUND like a CD?
4.  How many people will replace their broadcast receivers and VCR's if the
	digital format screws up the images of sports events?  How will
	advertisers feel about putting their commercials on events that
	don't boradcast very well?
5.  Have we really exhausted what we can do with lossless compression?  Have
    we really exhausted what we can do with reconstruction algorithms that
    look at successive cycles of audio signals to sneak around the Nyquist
    limits?  Are we solving the wrong problem?

Newsgroups: comp.compression