[Speex-dev] Question about UWB

[Jean-Marc Valin]

Quoting John Ridges <jridges at masque.com>:
> One question that I hope someone on the list just knows the answer to
> without having to delve too deeply into the code: How does UWB mode
> divvy up the bandwidth and pack it in the bitstream? I know from the
> documentation that WB mode codes the first 0-4K kHz band as a Narrowband
> packet, and then adds on the 4-8 kHz band coded separately (so that a NB
> decoder can decode a WB bitstream by just ignoring the second band;
> rather clever I thought), but it doesn't describe how UWB mode works.
> Does UWB keep the 0-4 kHz NB packet, and then add a 4-16 kHz UWB packet?
> Or does UWB contain both a NB and WB packet, and add a 8-16 kHz part? Or
> something completely different? I'm just trying to figure out which
> decode modes will decode which encode mode bitstreams. Thanks,

UWB just does a split into WB (0-8) and a 8-16 kHz band. That band is encoded
with only 1.8 kbps, so it's a bit of a hack. Some people actually prefer WB to
UWB, so YMMV. As you can expect, a UWB bit-stream can be interpreted as NB or
WB just by ignoring some bits at the end.

   Jean-Marc