"The EggKing" wrote in message
...
I'm not eactly sure how to word this but I must as it has bugged me for
some
time now:

If an encoder has a cutoff frequency (eg. 15KHz in NICAM), to prevent
aliasing or any other problems, is the 'shape' of he wave preserved within
the data produced?

The shape that is more-or-less preserved in the digital data would be that
of an analog signal low-pass filtered with a 15 KHz cutoff.

I mean to say; The higher frequencies that most of us
have no chance of hearing as pure sin waves (15K+) do shape the waveform
as
a whole.

Right, but if we don't hear them, then the shaping they cause is inaudible
as well.

If the higher frequency cannot be sampled is therefore the shape of
the wave altered in encoding?

Yes.

I'm thinking it must be as recordings lose depth and atmosphere.

Nope. The depth and atmosphere of a live performance that is often lost, is
already gone when you listen to the amplified analog electrical outputs of
the microphones, before any digital encoding.

It just puzzles me that even though we can't hear certain frequencies we
can miss
them when they're gone.

It might be puzzling because that's not how things work.

Crap, I think I've unwittingly wandered into SACD territory here......

I've been making recordings with strong content 15, 20, 22.05, 30 and even
40 KHz for a number of years. It takes some pretty expensive mics to capture
the 22 KHz stuff, but I've got 'em at my disposal. I've made recordings at
24/96 and I've listened to them via a number of different means.

I've also listened to these recordings with additional low-pass filtering as
low as 9 KHz, as have any number of others. They are on the web and people
can download and listen to them at their leisure.

Bottom line, even recordings with exceptionally strong content above 40 KHz
sound no different if sharply filtered at 16 KHz. Don't believe me? Download
and listen for yourself at www.pcabx.com .