Audio cut-off frequencies on London DAB - Radio

vinnielo · 06-11-2009, 17:52

I thought I'd measure the cut-off frequencies on London I and London II to have "in print" what's going on with the amount of treble that gets through.

CE London
Capital 14kHz (128k)
Heart 15kHz (128k)
Galaxy 15kHz (128k)
KISS 15kHz (128k)
Magic 12kHz (112k)
Heart 12kHz (112k)
Jazz FM 15.5+kHz (128k)
Chill 11.5kHz (64k full-rate sampling)
Sunrise Radio 11.5kHz (64k half-rate sampling)
Traffic Radio jumping between 8k and 8.5+kHz (48k half-rate sampling)

Switch London
Absolute Xtreme jumping between 14+k and 15kHz (128k)
BBC London Too much speech content to measure.
Gold 11.5kHz (112k)
XFM (no measurements taken)
Punjabi Radio jumping between 8+k and 9kHz (64k full-rate sampling)
Smooth Radio jumping between 14+k and 15kHz (128k)
Spectrum Radio jumping between 8+k and 9kHz (64k full-rate sampling)
THE HITS 11.5kHz (112k)
KERRANG jumping between 12k and 13kHz (80k full-rate sampling)
UCB UK jumping between 13.5k and 14.5kHz (96k full-rate sampling)

Some observations:
Jazz FM has the fullest sound at 128k
Capital FM is strangely cut-off at 14kHz.
A lot of volatile cut-offs (jumping about) on London II compared to London I.

Feel free to add other observations I might have missed.

hanssolo · 06-11-2009, 20:12

The 128k figures equal FM with the 15khz cutoff. Just of interest does the 160k of Absolute and Classic FM and the 192k of R3 meet 18khz?
Ofcom was supposed to have done "listening tests" to approve the new 112k state of the art encodecr over the older 128k encoders, but there does seem to be a lower cutoff.

A lot of older people can't hear over 12khz anyway! Maybe they did the listening test!

vinnielo · 07-11-2009, 01:35

My instrument (soundcard+CoolEdit) seems to have an offset introduced to it since my last use. Take away about 0.5k from the figures below before comparing with the London results.

(BBC Radio 3 can't be measured - the material is too quiet.)

Absolute and Classic (160k) are about 17kHz.
talkSPORT and Premier UK (64k half rate) at 11.5k.
Planet Rock and Amazing Radio (128k) at 15+kHz
BFBS Radio 16kHz

Radio 1, 1Xtra, Radio 2 and 6 Music all at 14.5kHz.

vinnielo · 07-11-2009, 01:52

Premier London (80k full rate) jumping between 12+kHz and 13kHz
Absolute Classic Rock (128k) 16kHz
Passion for the Planet (96k full rate) 14kHz
PRL (96k full rate) jumping between 14kHz and 15kHz
Q Radio (112k) 12+kHz
Panjab (64k half rate) 11.5kHz
Gaydar (128k) jumping between 14kHz and 14.5kHz
Dabbl (80k full rate) 15+kHz !! <- This ought to be how all 80k encoders are set up!!

hanssolo · 07-11-2009, 06:57

Quote:

Originally Posted by vinnielo

Absolute and Classic (160k) are about 17kHz.
talkSPORT and Premier UK (64k half rate) at 11.5k.
Planet Rock and Amazing Radio (128k) at 15+kHz
BFBS Radio 16kHz

Radio 1, 1Xtra, Radio 2 and 6 Music all at 14.5kHz.

Thanks for that, would have thought Absolute and Classic might have been higher, but might be the original encoders, still better than FM?
Guess BFBS must be using a new encoder to get 16kHz on 128k?

talkSPORT and Premier UK DAB at 11.5khz are better than on AM which I guess is about 5khz max in the UK?

chrisjr · 07-11-2009, 11:16

The big problem with exercises like these is that they make no allowances for the source material. How do you know that the frequency cut off is a consequence of the DAB encoding or because that is what the source is encoded to? Or there is some extra processing before the encoder that is rolling off the HF?

The only way to be certain is to get the radio station involved to do a frequency sweep directly into the input of the encoder. Now some may say that swept tone is more interesting than some of the programmes put out by certain stations but I suspect "the management" may have a different opinion

And of course how do you know the filters on the receive device are not affecting the result? It is an interesting exercise to do but is so full of unknowns that you cannot draw any real conclusions about it.

Inkblot · 07-11-2009, 11:23

Quote:

Originally Posted by vinnielo

(BBC Radio 3 can't be measured - the material is too quiet.)

Have you tried when they're playing contemporary jazz off CDs? As long as it's a recent recording it should have a full frequency range.

vinnielo · 07-11-2009, 15:43

Quote:

Originally Posted by hanssolo

Guess BFBS must be using a new encoder to get 16kHz on 128k?

Yes, but it also sounds the slushiest, which I'm guessing is to do with transcoding that's taking place in the chain.

Quote:

Originally Posted by chrisjr

The big problem with exercises like these is that they make no allowances for the source material.

Well, of course, but I'm measuring the most important part - what's actually coming out of the listener's speakers!

When I was praising Jazz and dabbl, I should make clear that I'm talking about the overall setup (including processing/filtering), and not commenting solely on the encoder itself.

vinnielo · 07-11-2009, 16:17

LBC 97.3, NME Radio and FUN kids (80k full rate).. as good as dabbl at 15+kHz. I would guess all these stations are using hardware encoders.
LBC 1152 jumping between 8k and 8.5+kHz (48k half-rate sampling)

BBC Radio 3 @160k, 16.5+kHz
BBC Radio 7 @ 80k full rate, 11.5kHz (considerably lower than dabbl, but this could be deliberate, since it's a speech station)
BBC Asian Network @ 64k full rate, 11.5kHz.

vinnielo · 07-11-2009, 16:24

Quote:

Originally Posted by vinnielo

I thought I'd measure the cut-off frequencies on London I and London II to have "in print" what's going on with the amount of treble that gets through.

CE London
Capital 14kHz (128k)
Heart 15kHz (128k)
Galaxy 15kHz (128k)
KISS 15kHz (128k)
Magic 12kHz (112k)
Heart 12kHz (112k)
Jazz FM 15.5+kHz (128k)
Chill 11.5kHz (64k full-rate sampling)
Sunrise Radio 11.5kHz (64k half-rate sampling)
Traffic Radio jumping between 8k and 8.5+kHz (48k half-rate sampling)
.

Sorry, that should be Heat at 112k.

06-11-2009, 17:52	#1
vinnielo Forum Member Join Date: Jan 2002 Location: South East England Services: FTA: 28.2, 19.2, 13, London DTT, TV->PC capture, 2Mb fibre. London/S&C DAB Posts: 3,848	Audio cut-off frequencies on London DAB I thought I'd measure the cut-off frequencies on London I and London II to have "in print" what's going on with the amount of treble that gets through. CE London Capital 14kHz (128k) Heart 15kHz (128k) Galaxy 15kHz (128k) KISS 15kHz (128k) Magic 12kHz (112k) Heart 12kHz (112k) Jazz FM 15.5+kHz (128k) Chill 11.5kHz (64k full-rate sampling) Sunrise Radio 11.5kHz (64k half-rate sampling) Traffic Radio jumping between 8k and 8.5+kHz (48k half-rate sampling) Switch London Absolute Xtreme jumping between 14+k and 15kHz (128k) BBC London Too much speech content to measure. Gold 11.5kHz (112k) XFM (no measurements taken) Punjabi Radio jumping between 8+k and 9kHz (64k full-rate sampling) Smooth Radio jumping between 14+k and 15kHz (128k) Spectrum Radio jumping between 8+k and 9kHz (64k full-rate sampling) THE HITS 11.5kHz (112k) KERRANG jumping between 12k and 13kHz (80k full-rate sampling) UCB UK jumping between 13.5k and 14.5kHz (96k full-rate sampling) Some observations: Jazz FM has the fullest sound at 128k Capital FM is strangely cut-off at 14kHz. A lot of volatile cut-offs (jumping about) on London II compared to London I. Feel free to add other observations I might have missed.

06-11-2009, 20:12	#2
hanssolo Forum Member Join Date: May 2004 Posts: 4,157	The 128k figures equal FM with the 15khz cutoff. Just of interest does the 160k of Absolute and Classic FM and the 192k of R3 meet 18khz? Ofcom was supposed to have done "listening tests" to approve the new 112k state of the art encodecr over the older 128k encoders, but there does seem to be a lower cutoff. A lot of older people can't hear over 12khz anyway! Maybe they did the listening test!

07-11-2009, 01:35	#3
vinnielo Forum Member Join Date: Jan 2002 Location: South East England Services: FTA: 28.2, 19.2, 13, London DTT, TV->PC capture, 2Mb fibre. London/S&C DAB Posts: 3,848	My instrument (soundcard+CoolEdit) seems to have an offset introduced to it since my last use. Take away about 0.5k from the figures below before comparing with the London results. (BBC Radio 3 can't be measured - the material is too quiet.) Absolute and Classic (160k) are about 17kHz. talkSPORT and Premier UK (64k half rate) at 11.5k. Planet Rock and Amazing Radio (128k) at 15+kHz BFBS Radio 16kHz Radio 1, 1Xtra, Radio 2 and 6 Music all at 14.5kHz.

07-11-2009, 01:52	#4
vinnielo Forum Member Join Date: Jan 2002 Location: South East England Services: FTA: 28.2, 19.2, 13, London DTT, TV->PC capture, 2Mb fibre. London/S&C DAB Posts: 3,848	Premier London (80k full rate) jumping between 12+kHz and 13kHz Absolute Classic Rock (128k) 16kHz Passion for the Planet (96k full rate) 14kHz PRL (96k full rate) jumping between 14kHz and 15kHz Q Radio (112k) 12+kHz Panjab (64k half rate) 11.5kHz Gaydar (128k) jumping between 14kHz and 14.5kHz Dabbl (80k full rate) 15+kHz !! <- This ought to be how all 80k encoders are set up!!

07-11-2009, 11:16	#6
chrisjr Forum Member Join Date: May 2004 Location: Reading Services: Freeview [LG TV, Humax PVR], DAB [Technics], Wireless Broadband [Now] Posts: 7,521	The big problem with exercises like these is that they make no allowances for the source material. How do you know that the frequency cut off is a consequence of the DAB encoding or because that is what the source is encoded to? Or there is some extra processing before the encoder that is rolling off the HF? The only way to be certain is to get the radio station involved to do a frequency sweep directly into the input of the encoder. Now some may say that swept tone is more interesting than some of the programmes put out by certain stations but I suspect "the management" may have a different opinion And of course how do you know the filters on the receive device are not affecting the result? It is an interesting exercise to do but is so full of unknowns that you cannot draw any real conclusions about it.

07-11-2009, 16:17	#9
vinnielo Forum Member Join Date: Jan 2002 Location: South East England Services: FTA: 28.2, 19.2, 13, London DTT, TV->PC capture, 2Mb fibre. London/S&C DAB Posts: 3,848	LBC 97.3, NME Radio and FUN kids (80k full rate).. as good as dabbl at 15+kHz. I would guess all these stations are using hardware encoders. LBC 1152 jumping between 8k and 8.5+kHz (48k half-rate sampling) BBC Radio 3 @160k, 16.5+kHz BBC Radio 7 @ 80k full rate, 11.5kHz (considerably lower than dabbl, but this could be deliberate, since it's a speech station) BBC Asian Network @ 64k full rate, 11.5kHz.