[Walt]

Geluso wrote:

Can anybody tell me the frequency response of XM broadcasts. It is
general knowledge that the frequency response of FM broadcasts is
basically 30Hz-20KHz.

The spec for FM calls for response out to 15khz, with a fairly steep
rolloff above that. The stereo pilot tone is at 19khz, and for that to
work there can't be any audio signal that high.

That said, the sound quality issues with FM are not due to inadequate
response above 15k. For one thing, very few people can hear above 15k.

In contrast, despite quite a bit of research,
I have been unable to locate any mention of XM's frequency response
whatsoever.

I'm not sure. But again, the frequency response is not the issue. See
below.


I would like to know XM's frequency response because I just bought a
Polk XRt12 Home XM Tuner, which is suppose to be one of the best XM
receivers available, yet I am extremely disappointed in its sound
quality. In addition to very poor stereo separation, the music is
completely washed out. Brilliancy is non-existent. The highs are
dull, and the midrange is muted. Even the human voices are muffled.

Welcome to the world of digital audio compression. You describe the
artifacts quite well. You might add that the soundstage is flat,
two-dimensional with no depth or sense of space. That's what happens
when you throw away all those bits that you supposedly can't hear.

True, I have heard many negative comments regarding XM's compressed
signal. But I have also heard from numerous sources that XM
delivers near CD-quality sound.

Don't beleive the hype. XM isn't CD quality. Not even close.

It is this significant discrepancy
of opinion that has led me to seek a quantifying answer to XM's
frequency response.

The answers lie in a) what bit rate are they using (64k? 128k? ) and
b)what compression algorithm are they using.


The very poor sound quality that I am getting out of my Polk
receiver puzzles me, because when I had the opportunity to listen to
XM's programming through a DirecTv system, the sound quality was
superb. Does anyone have an explanation for this great difference?

Perhaps it was a different bit rate on the other system? Or the
material was chosen to minimize the compression artifacts?

//Walt