On 07/02/12 11:59 AM, Rick van Rein wrote:
> Hello Bruce,
>
>> Did you use Jean-Marc's statistical methods in retraining the codebook?
>
> The codebook in Codec2 is just a Cartesian product, so there
> was no need to retrain anything. Also, this patch does not
> change anything at that level of the code.
I assume that Bruce was referring to the LSP VQ codebook training I was
working on with David, but it seems like you're using the "old" scalar
VQ, right? In any case, there would like be some retraining/retuning
required for 12.8 because you would probably need more than 10 LSPs.
Possibly 12 to 16 LSPs.
>> How does this differ from Opus at that rate? Or does Opus not get that low?
>
> I had never heard from Opus, but according to opus-codec.org it does not go
> below 6 kb/s.
Actually, Opus mediumband (12 kHz sampling rate) starts at around 8-10
kb/s, so definitely no overlap between codec2 and Opus there.
> Please note that I am not proposing any change to the wire format
> for Codec2 with this patch; I am merely suggesting to exploit the
> full time domain size of the FFT (processing 512 instead of 320 samples
> en bloc) and deal with the slightly altered frequency domain that
> follows from it. It's very simple work, really. It may just have
> a big impact on quality, that's all :-)
Actually, you can't just change the sampling rate without changing
anything else. You not only need to use more than 10 LSPs, but there may
be implications for the pitch (encoding and search), the VAD and maybe
more.
Cheers,
Jean-Marc
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