Frequency Response of XM
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. In contrast, despite quite a bit of research,
I have been unable to locate any mention of XM's frequency response
whatsoever.
The standard FM bandwidth is: +/-0.5 dB, 30 Hz to 15 kHz.
"Audio channels on XM are digitally compressed using the aacPlus codec
from Coding Technologies for most channels, and the AMBE codec from
Digital Voice Systems for some voice channels." -- Wikipedia
And, depending on how the system is decoded in your head-end, that
could cut off anywhere around 12Khz or so.... which from what I
understand (purely by anecdote) seems about typical.
The AMBE codec, BTW, is what satellite phones use and is limited to
voice-frequencies only... which makes sense, after all.
Keep in mind that XM (and Sirius) were designed against the automotive
environment. Subtle nuances are not required, and furthermore would
chew up bandwidth... can't have that, can we? Don't expect such a
system to translate well to home audio.
Small Political Rant: Once upon a time, not so very long ago, Radio and
Television were OTA, free, and somewhat varied (at least radio was
such). With the gutting of the FCC, the onset of protected cable
companies and the general impatience of Americans, OTA is largely being
displaced by fee-for-service delivery systems, cable, satellite and
so-forth. Accordingly, the OTA outlets are struggling and
consolidating, and excepting public and college stations, seriously
dumbing down. The AM and FM bands as we know them are threatened (as
well as OTA television) and there is a push to eliminate them
altogether... to be replaced by fee-for-service systems. When one has
to pay for it, Speech ain't nohow free.
Write/call/e-mail your representatives in Washington. The "people" own
the airwaves, not the corporations, so take them back. Put some teeth
back into the FCC.
Peter Wieck
Wyncote, PA
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