Re: DRM
- From: "DAB sounds worse than FM" <dab.is@xxxxxxxxxxx>
- Date: Wed, 02 Nov 2005 12:48:31 GMT
Kryten wrote:
> "DAB sounds worse than FM" <dab.is@xxxxxxxxxxx> wrote in message
> news:2fO9f.28945$65.28363@xxxxxxxxxxxxxxxxxxxxxxx
>
>> You can decode DRM using a quickish DSP chip. Remember that general
>> purpose CPUs in a PC aren't optimised for DSP tasks.
>
> Modern PCs do seem to have accelerators on-chip for processing the
> multimedia applications (known long ago as MMX capability).
And SSE.
> They're
> up to the job of a lot of DSP.
I'm not saying they're not.
> I'm not keen on writing a load of DSP software, or debugging an
> analogue RF front end. I wonder if the DSP job is simple enough for a
> modest FPGA?
If you don't want to use an RF front-end to reduce the bandwidth then
you'd have to sample at twice the bandwidth, which would be 60
Msamples/s for a 30 MHz bandwidth (due to Nyquist), and also you'd have
problems because the ADC would have to accommodate the largest signal
power, but you'd also want to receive signals with low signal power.
Basically, you really need to use an RF front-end. It's not impossible
to go without one, and BBC R&D built a DRM receiver without one, I
think, but it's far easier with one.
> From what I recall, DAB modules guzzled power. The Elektor DRM
> receiver seems fairly minimal, no custom RF/analogue ASICs, etc.
The Elektor circuit is just an RF front-end:
"The receiver is of a
surprisingly simple design and supplies a 12-kHz output signal for easy
connection to your PC's soundcard which handles the demodulation and
MPEG
decoding."
The PC software does all the demodulation and decoding.
> I thought DRM was an inferior MW substitute for VHF DAB, but now I
> suspect the DRM system is not tied to any particular carrier
> frequency - although MW has its pros.
> Incidentally I've also taken a peek at Ogg/Vorbis. This is royalty
> free and allows for lossless companding too. Maybe DRM could
> accommodate the occasional lossless broadcast...
There's not enough bandwidth to do lossless. They're talking about
increasing the bandwidth to 50 to 100 kHz, so you'd be looking at around
a max bit rate of 200 to 300 kbps, which isn't large enough for
lossless.
--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info
Please sign the petition asking the BBC to provide better audio quality
on its radio stations on DAB, Freeview, satellite and cable:
http://tinyurl.com/a68e4
.
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