BBC Planning MP3 Downloads

The BBC are planning to get in on "the iPod effect" by making some of their radio shows available as MP3 downloads. Only the Reith Lectures on Radio 4 are available at the moment, and the BBC will monitor the reaction before deciding on its policy, which may lead to archive material being made available for MP3 download.

The file available is only 64kbps joint stereo, but is using a sampling rate of 22.05 kHz, rather than the usual 44.1 kHz sampling rate for music MP3 files. The use of 22.05 kHz is sensible for an MP3 download for speech content (because MP3 downloads are unicast, which require a lot of bandwidth compared to broadcast or multicast systems, so low bit rates are excusable for BBC internet downloads, and low sampling rates improve the audio quality for such low bit rate streams), because the frequency content of speech predominantly can be encoded using this low sampling frequency. It will be interesting to see what bit rate they use for music MP3 download files though, because this low sampling frequency is not high enough for music content, which requires a sampling frequency of at least 32kHz, which will in turn require a higher bit rate for a similar level of audio quality.

Listening to the file makes it all too clear that MP3 would have been the better choice of codec (COder/DECoder) to use for DAB instead of MP2, because MP2 would have a far lower audio quality than this file has. And, indeed, the 98% of 128kbps stereo radio stations on DAB in the UK would all sound far better if the MP3 codec had been used instead of MP2 for DAB.

I think it is a very good move to make radio shows available for downloading, and have recently been thinking that although the BBC Radio Player has proved to be successful, the audio quality of the shows are unnecessarily low, presumably to make the BBC's life easier, and to avoid confusion amongst consumers.

The new BBC Chairman, Michael Grade, recently commented on broadcasters using the internet as a distibution method by saying

"The lessons are you can't be arrogant enough to believe any of the distribution methods available are going to win out. You have to play them all. I'd be availing myself of every possible opportunity to distribute my content and I'd let the consumer decide."

and I'd go further than this because there are codecs available that are far superior to MP3 (such as AAC (which can be used on iPods) and high-efficiency AAC), and it would be desirable if the BBC made their content available encoded in these formats as well as in MP3 format. For example, if/when the BBC make music content available for download in MP3 format, the audio quality of 96kbps AAC is, as can be seen on here, far better than 128kbps MP3 (the MP3 curve is labelled 'LIII'), and high-efficiency AAC at 64kbps would likely be better than 128kbps MP3 as well.

For example, the current BBC Radio Player uses a bit rate of about 45kbps when the listener has a broadband internet connection (although the bit rate is variable). At this low bit rate level the high-efficiency AAC codec would be a better choice than the Real Player codec. Also, as internet bandwidth is following a similar trend to Moore's Law (i.e. doubling every couple of years or so), then it is hoped that the BBC will increase the bit rates of their internet streams in the future.

If the BBC did increase the bit rates of their internet radio streams, and allowed users to use the improved codecs, then the audio quality of their internet streams could actually be very good. Although the high-efficiency AAC (HE AAC) codec is relatively new, it is not inconceivable that the BBC could increase the bit rates of their internet streams to 64kbps, and at this bit rate the HE AAC codec would provide audio quality that is vastly superior to the audio quality of the Real Player streams at around 45kbps on its BBC Radio Player.

For technical information about AAC and HE AAC, see:

http://www.telos-systems.com/news/reprints/rw_092601_aac.pdf (AAC, 1.06 MB)

http://www.telos-systems.com/techtalk/hosted/HE-AAC.pdf (HE AAC, 538 KB)

And if you want to try encoding audio into AAC format there's a good (free) codec here:

http://dl2.afterdawn.com/aacenc_v215.zip (731 KB)

The encoder is controlled from the command line (Command Prompt from Accessories in Windows) and read the index.pdf file for instructions of how to encode once you've downloaded the Zip file. There's also a Winamp plug-in in the Zip file. If you don't want to use the command line then there's a GUI here:

http://www.rarewares.org/files/aac/psyteldrop.zip (135 KB)

Alternatively, both an AAC and HE AAC codec are available in the Nero CD/DVD program, and an AAC codec is available with the software you get with an iPod.

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