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What happens to The Proms after the Royal Albert Hall?

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Mark Kortekaas Mark Kortekaas | 16:17 UK time, Monday, 19 October 2009

Earlier this year, we broadcast another fantastic season of the BBC Proms. Every concert is broadcast live on BBC Radio 3, with some concerts also broadcast on television - mainly BBC Four, but also BBC HD, BBC Two and BBC One. That meant many live broadcasts live from the Royal Albert Hall - a building which is a number of miles away from Radio 3's studios in Broadcasting House. So how does the audio get from the Royal Albert Hall into my FM/DAB/Internet Radio at home? And what happens to it along the way? How much is the audio in the Royal Albert Hall "dynamically compressed" (where the quiet bits get louder and the louder bits get quieter), and is any of the audio signal chucked away by using bandwidth limiting? And how might you get the best quality from our Proms coverage? I've always been interested in this; so here's what happens: For Radio 3 transmission, on iPlayer and others
  • The Radio 3 stereo mix is sent from the Albert Hall to Broadcasting House via a high-quality 24-bit 48 kHz digital circuit and then fed to Radio 3 FM, DAB, Freeview, Freesat & Online services. The microphones within the Royal Albert Hall handle frequencies from a few Hertz to over 20kHz and there is no LF or HF filtering added to the main microphone feeds.
  • Radio 3 FM is bandwidth-limited to 15 kHz, with DC filtering applied. The FM signal has dynamic range compression applied via an Optimod processor. The signal is NICAM encoded at 676kbps and fed to the FM transmitters via the BBC's distribution network. No further bandwidth limiting is applied.
  • The feed from the Royal Albert Hall is also fed to Radio 3 on DAB, Freeview and Satellite. These operate at 192kbps, although this reduces to 160kbps on DAB at some points in the schedule to accommodate 5 Live Sports Extra on the DAB multiplex. There is no other processing applied to the signal.
  • On the BBC iPlayer's listen-again services, Radio 3 is available at 192kbps AAC. This is processed in the same way as DTT ("Freeview"). Live streaming is also available, at 192kbps Windows Media and other versions.
For BBC Four transmission
  • BBC Four uses the same stereo mix that's used for Radio 3. It's combined with the pictures and sent back to Television Centre via an MPEG2 (MPEG1 Layer II) link at 384kbps. No additional processing is carried out before encoding.
  • BBC Four sound on Freeview, Freesat and Sky is transmitted (using MPEG2) at 256kbps with no processing or bandwidth limiting.
For BBC Two and BBC HD (also BBC One) transmission
  • Proms on BBC Two (and BBC One) use a dedicated sound mixing truck, to ensure that audio is mixed in a complementary way to the pictures broadcast. Proms also transmitted on the BBC HD Channel are usually mixed in surround sound using Dolby 5.0, though broadcast in Dolby 5.1 for technical reasons.
  • Stereo for BBC One, BBC Two and BBC HD is sent back to Television Centre via an MPEG2 (MPEG1 Layer II) link at 384Kbps.
  • When available surround sound is sent back in the same link using Dolby E encoding at 2Mbps (Dolby E can support up to 8 channels).
  • Stereo is transmitted on BBC One, BBC Two at 256kbps (MPEG2), and 256kbps (MPEG4) on BBC HD.
  • Surround sound is transmitted on BBC HD at 384kbps using Dolby Digital encoding. Dolby Digital has a frequency range from about 3 Hz to 18 kHz.
  • Only the surround sound mix is transmitted on BBC HD. If an HD set top box is set to "Stereo" it uses the additional data (Dolby Metadata) we send in the Dolby Digital signal to create a stereo mix.
  • BBC television analogue services use NICAM-728 encoding the stereo signal at 728kbps for transmission.
Of course it should be noted that various transmission chains have their own issues depending on the output. For instance the Freeview signal is MPEG coded, filtering happens as part of the coding process, in a 32 segment polyphase band pass filter. The AAC encoding does its own thing, etc. With that in mind, the feeds are really filtered to you as the end listener. I'm grateful to Andy Quested from BBC HD, and Neil Pemberton from BBC Radio 3 for compiling these answers.

Comments

  • Comment number 1.

    Why aren't things like the Last Night of The Proms released on Blu-ray too?

  • Comment number 2.

    Also, are they going to ever replace the opera singers on it with normal singers instead please?

  • Comment number 3.

    Very interesting - thank you!
    One thing I'm still wondering - what is the format of the audio in the BBC HD version on iPlayer? Is this the 5 channel version?
    Which would be the highest quality on iPlayer, the audio stream of BBC HD, or the 192k AAC stream from the Radio 3 broadcast?

  • Comment number 4.

    I expected a rather different article from the title, but this was very interesting. As far as radio broadcasts go, I pretty much knew it already, though the DAB bandwidths were interesting regarding R5LE. I'd be interested to know just how much dynamic range compression is applied to FM broadcasts. It can't be much; unfortunately my reception was pretty poor this summer, and quiet passages were inaudible thanks to interference! I once read that Radio 3 has the greatest dynamic range of any FM station in the UK.

    What I was expecting from the title: details of what happens to the recorded footage when the Proms season is over. Think of all those unique concerts — the premieres, special commissions, one-off performances — that have occurred over the recorded history of the Proms. How much of this has been kept? I look forward to the day when any Proms performance from the last 50-70 years could be called up on iPlayer.

  • Comment number 5.

    Web iPlayer - 'HD' content - audio is presented as 192kbps stereo AAC-LC.

    iPlayer 'HD' on Virgin Media is presented as 256kbps MPEG1 Layer 2 audio.

    So - in answer to @rhughes2832 - the Web iPlayer 'HD' is equivalent of the R3 Simulcast stream.

    Interesting comparison between 192kbps AAC-LC and 256kbps MP1L2 - in prior listening test we've done (so not a specific test for this comparison) I would find an 'average' ear not hearing much difference between those two. Although a 'golden' ear would hear certain compression artefacts.

    Alan

  • Comment number 6.

    Mark/Alan,

    Please would you be kind enough to explain why you use AAC inside flash on iPlayer and WMA for live radio internet streams?

    I've noticed that the Five Live WMA stream is usually significantly behind every other way of listening including iPlayer, Sky, DAB and AM. It's not just a little bit either (30-60 seconds).

    Are you planning to make the AAC streams directly accessible?

    Many thanks

    K

  • Comment number 7.

    LOL

  • Comment number 8.

    All this user's posts have been removed.Why?

  • Comment number 9.

    You say : "On the BBC iPlayer's listen-again services, Radio 3 is available at 192kbps AAC".
    On the iPlayer messageboards a couple of weeks ago I asked why the pop-up on R3 listen-again streams shows 128kbps - as eg.:
    "BBC Media Player v.2.20.14200.14320
    b00n6zbx | 128kbps | aac | LI"
    Though you responded briefly, asking for more details, you haven't reported back.. so I'd still be interested to know whether the streams are actually being delivered at 128 or (as another poster suggested) at 192 but simply showing 128 in error.

    Regards

    Walter

  • Comment number 10.

    The 192kbps stereo AAC-LC may not be perfect, but it's definitely good enough for me most of the time.

  • Comment number 11.

    Very good - a very informative article - thank you. But I was surprised to read that (by inference) R3 DAB and iPlayer feeds have no DRC applied..? - according to other sources they do: http://www.digitalradiotech.co.uk/audio_processing.htm

    Also surprising is that R3 Listen Again "is available at 192kbps AAC". In my experience it is invariably at 128kbps (though Listen Now is indeed at 192kbps)

    I have been struggling with the problem of how best to record BBC Proms via R3 (strictly for my own use). I am very conscious of quality. Having experimented last year with DAB and iPlayer, I decided this year to settle on FM. The results have been very much better, with greater ambience and clarity.

    Then I heard about the new XHQ streaming service. I decided to compare this with FM. I listened to FM using a dedicated FM Hi-Fi tuner with 8-element vertically polarized yagi directed on the Marlborough Tx, 4.7 miles line-of-sight - with noise-free reception. I listened to XHQ using a Dell XPS-700 with integrated sound card. In both cases I listened with identical Sennheiser HD550 headphones (I have two such headphones).

    I listened to two Proms performances, making rapid changes between the two sources up to one hundred times in total. I listened to the Four Last Songs from Prom 66 and the Pines of Rome from Prom 69.

    I can say that XHQ was very good indeed - superlative in fact. I could not find any fault. FM was very close - almost identical in ambience and clarity but I noticed some difference in the loudest passages. For example in the final part of Pines of Rome, the XHQ feed had greater volume with apparently more 'headroom' and with greater clarity.

    The difference was (I believe) due to the DRC applied to the FM signal. But the difference was quite minor and most people would not notice at all without such a direct comparison. Apart from the effect of DRC I could not notice any real difference - both delivered a "being there" experience with very good clarity, separation, and ambience.

    I was hoping that the XHQ feed may yield less "audience percussion" - the constant gutteral honking, hawking, and hacking noises that seem, very sadly, to be a mandatory accompaniment to some of the most sublime moments in musical creation. My faint hope was raised due to the purportedly lower (or non-existent??? - someone please answer) DRC on XHQ feed. Alas no - I heard it all too plainly - indeed there were also some astonishing bangings and crashings going on, from somewhere in the audience, while I was listening to the XHQ feed.

    Conclusion: I would love to be able to record the XHQ feed from R3. As it happens I can (though only while the Proms are on) - by virtue of having an old IBM X31 that will record off the Internet (newer computers seem to have censored this capability). Once the Proms are over it is back to 192kbps, or 128kbps for Listen Again with the somewhat 'recorded in the toilet' sound.

    The problem is there are too many 'ifs andd buts' to the XHQ feed at the moment, at least if you can't be around at the time and instead want to record the sound.

    So in practice, if like me you can't be around at time the Proms performances are actually happening and want to record them instead, _and_ you don't particularly fancy the 'in the toilet' sound then there is only one option: FM

    To my ears FM delivers quality that is mostly indistinguishable from the XHQ sound, and most importantly the quality is available ALL of the time, not just when the Proms are on. And... you can record using the standard Line In socket without being dependent on an increasingly rare computer that will record off the Internet.

  • Comment number 12.

    pgp566 asks about recording the XHQ stream. It is very easy to make a perfect recording on any PC, irrespective of the quality of the soundcard. Use Total Recorder, which is very inexpensive ($20 or so). This will record the wave file generated by Flash *before* it reaches the soundcard, so it is not affected in any way by the quality of the soundcard or other audio circuitry in the computer. From that, you can make whatever sort of recording you like. It will translate into CD without any further processing or loss.

  • Comment number 13.

    Cantobell's comment was very helpful. I have installed Total Recorder and it delivers the best quality I have so far achieved even on a computer with a clobbered sound card (but good otherwise). This was at 192kbps - I wish I could try it with XHQ. I now realise my mistake with FM - the DRC is clearly visible in the Cool Edit 2000 waveform, compared to the streaming waveform recorded via Total Recorder. And I can now hear the DRC as well. But is it just me or is there more DRC on FM than there used to be? Is this just to do with FM channel spacing or is there another purpose? Thanks, and please keep up the very informative posts!

 

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