In article , Tim Anderson wrote:
I'm interested in SACD technology. But I'm puzzled by this:

http://interprod5.imgusa.com/son-637/technology.asp

"Unfortunately, the PCM process exposes the music to a "decimation"
filter during recording and an "interpolation" filter during playback.
These two filters can smear the sound, corrupt the sense of space
around the instruments and sacrifice the subtleties of live music."

I won't comment on the "unfortunately" bit. Someone else may.

- What do the quotation marks signify?

It means that amongst the DSP (Digital Signal Processing) community
the words have a conventional (jargon) meaning intended for brief but
accurate communication between experts which is different from the
dictionary meaning. Unfortunately these words are then (mis-)appropriated
for marketing purposes despite the retention of the quotation marks.

- "Decimation" means "killing every tenth man", according to my
dictionary. What's that all about?

Start by translating that as "killing every tenth sample". But it
isn't just used about getting rid of every tenth - the DSP world uses
the word for any process which removes samples from the digital audio
stream leaving a lower sample rate.

- I think I understand "Interpolation" which is about filling in
a missing value with a guessed value. Isn't that more to do
with error handling?

It can be used for handling errors where a sample is genuinely missing
due to an error and has to be re-created but interpolation is also
used (more often) for any process which increases the sample rate by
introducing more samples continuously.

Or this:

"The Direct Stream DigitalT pulse train "looks" remarkably
like the analog waveform it represents. More pulses point
up as the wave goes positive and down as the wave goes negative."

- How do I "look" at a pulse train?

You actually don't because SACD is encrypted, but I have seen diagrams
which draw the analogue representation of the stream's 1s and 0s on a
page with a pen whose line width is a reasonable fraction of the maximum
data rate. It does seem to create a visual approximation of the original
signal's amplitude.

- What are the benefits of this "look" to the audible results?

Ah. That's more difficult.

--
John Phillips