Taperssection.com

Gear / Technical Help => Ask The Tapers => Topic started by: dcaley on March 29, 2006, 11:49:24 PM

Title: UK DAB Question - bitrate/compression, etc
Post by: dcaley on March 29, 2006, 11:49:24 PM

hi folks,

i had a friend today record an xfm session for me through NTL Digital > TV > PC Audio card (WAV)

my questions for this recording are:

1. does NTL Digital compress this stuff to, say, 192kbps, or is there anyother way to note the bitrate, frequencies, or whatever?
2. this was not done over satellite, but rather terrestrial cable. does that make any difference?
3. i found a post on here (http://taperssection.com/index.php?topic=16969.0) and the person says there are no frequencies above ~15kHz. meaning anything recorded DAB > * is lossy?

hope those questions are accurate. any help would be great.


thanks,

dave

Title: Re: UK DAB Question - bitrate/compression, etc
Post by: sml42 on March 30, 2006, 07:19:07 AM

Hi,

It is definately lossy. I wasn't able to find a definitive bitrate from searching, but it is likely either 160kbit/s or 192kbit/s. A couple of useful links:

http://www.digitalradiotech.co.uk/dab/digital_radio_bit_rates.htm
http://www.ntl.com/locales/gb/en/guides/anoraks/

I don't have NTL (despite living ~15min from NTL HQ they passed by our village when laying fiber... bastards!) but perhaps there is an option on the ntl box to show bitrate? It is worth noting that terrestrial DAB broadcast (audio only) is generally at a lower bitrate than where it is broadcast along with digital TV (satellite,freeview,presumably ntl). I believe this is because digital TV broadcasts have a ton more bandwidth available.

Hope this helps..

best regards,
stephen

Title: Re: UK DAB Question - bitrate/compression, etc
Post by: dcaley on March 30, 2006, 09:03:10 AM

thanks alot! that first link pretty much solved the questions. going by that chart my recording is most likely 128kbps. unfortunate, as it is a sweet set by the raconteurs. hopefully someone out there has a true FM recording of it. this shall suffice for now, though.


thanks again,


dave

Title: Re: UK DAB Question - bitrate/compression, etc
Post by: nihilistic0 on April 05, 2006, 01:06:14 AM

does xfm has a limited frequency similar to regular FM radio?

Title: Re: UK DAB Question - bitrate/compression, etc
Post by: sml42 on April 08, 2006, 12:16:13 PM

xfm IS a regular fm radio station. It just happens to be local to London. FM coverage doesn't extend very far (I'm about an hours drive from London and can't pick up xfm). I think xfm has been around for years, it's only recently with the spread of digital radio that xfm is starting to get decent coverage.

Title: Re: UK DAB Question - bitrate/compression, etc
Post by: nihilistic0 on April 10, 2006, 02:02:16 AM

According to wikipedia, fm only broadcasts 50-15kHz

So, if xfm  is similar in this regard, then your 15kHz cutoff is perfectally normal

Title: Re: UK DAB Question - bitrate/compression, etc
Post by: sml42 on April 10, 2006, 05:28:26 PM

sorry, I think I see the confusion. "xfm" is the name of the radio station.  like "kroq" or "kcrw". It's a regular radio station, they broadcast a regular FM signal - provided you are close enough to the transmitted to get a signal. The station is also available in lossy digital via certain satellite / cablecos.

Yes, FM has a 15kHz bandwidth, 16kHz if you're lucky. Low-quality mp3 also tends  to have little signal over 15-16kHz. (and for the record, satellite/cable digital audio is basically mp3). There is a world of difference between a 15kHz FM signal and a mp3, but that's another discussion entirely :)