[mr_bill]

Do CDs have any output above 22khz?
Is that where the 'brick wall' filtering takes place?
How about if a CD is upsampled - does that add any output above 22khz?

As I understand, LPs, SACD and other high res software (downloads, DVDa) may contain output above 22khz.

I'm trying to understand the advantage or need for a super tweeter, extended response, with the different software, if I only listen to standard CDs.

[BobRex]

CDs have nothing above 22kHz.  Upsampling attempts to fill in the blanks, but it needs 2 end-points in order to work, so it can't do anything above 22k either.  Basically, anything recorded with redbook standard (44kHz sampling rate), or downsampled to accomodate CD will never have any response above 22k.

[mr_bill]

Thank you Bob - that is helpful.

[dmckean]

Anything on an LP above 22 Khz certainly isn't going to be music. There's a low pass filter applied during the cutting process as not to overwhelm the cutting head. SACD, DVD-A, Blu-Ray and hi res music files are the only place you're going to get this.

[dB Cooper]

CD cuts off at 20kz, the bandwidth between 20k and 22k is required for the filter to work. afaik